KR20000039139A - Method of tempering cryogenic carbon steel by inputting recarburizing agent in vacuum degasifying - Google Patents

Abstract

PURPOSE: A tempering method is provided to improve purity of molten metal and to reduce producing cost by minimizing oxygen after decarburizing work without interrupting decarburizing work in vacuum degasifying process. CONSTITUTION: In a tempering method decarburizing and deoxidizing by flowing back the molten metal received in a ladle to a vacuum tub of a vacuum decarburizing line, a recarburizing agent from 0.09kg to 0.28kg per 1 ton of molten metal is input to the vacuum tub when the residual amount of oxygen before decarburizing is 400ppm and higher. The recarburizing agent is input dividedly from 0.03kg to 0.47kg per 1 ton in one time in decarburizing process within 2 and 5 minutes after starting flowing back.

Description

Refining method of ultra low carbon steel by adding charcoal during vacuum degassing

The present invention relates to a method for refining ultra-low carbon steel used as a material for automobiles, home appliances, and more, and more specifically, to improve the cleanliness of molten steel by minimizing dissolved oxygen by incorporating a carbonization agent in a vacuum degassing and refining process. It relates to a refining method.

Ultra low carbon steels with a carbon content of less than 70 ppm are commonly used in materials such as automobiles and home appliances. Recently, as the demand for high quality steels increases, vacuum degassing is performed after the converter has been pulled out. The rate is increasing.

Vacuum degassing is the main purpose of manufacturing ultra-low carbon steel by reducing the components such as hydrogen and nitrogen by refluxing molten steel after tapping at low pressure or inducing decarburization and deoxidation by CO gas generation. In addition, the purpose is to obtain clean steel by floating separation of inclusions in molten steel by reflux. In the refining process of such ultra-low carbon steel, molten steel in each process is changed as shown in Table 1 below.

division Crusher Termination Initial start of vacuum degassing 12 to 20 minutes after the start of vacuum degassing (before deoxidation) Molten steel temperature (℃) 1650-1680 1605-1630 1580-1600 Carbon content (ppm) 300-500 300 to 480 70-20 Oxygen content (ppm) 500-800 350-600 300-450

The vacuum degassing process in the refining process of such molten steel will be described in more detail with reference to FIG. 1 as follows. The molten steel at the termination point as shown in Table 1 is pulled out from the converter into the ladle 1, and then the reflux tube 3 of the RH is deposited on the molten steel 2 accommodated in the ladle 1 to obtain a vacuum pump of the RH. When the inside of the vacuum chamber 1 is depressurized using h), the inside of the vacuum chamber is gradually depressurized to reach several torr. At this time, the molten steel of the ladle is raised into the vacuum chamber through the deposition tube so that the decarburization reaction and the degassing operation are performed in the vacuum chamber for about 12 to 20 minutes.

After decarburizing as described above, in order to remove oxygen components in molten steel, aluminum as a deoxidizer is added, and molten steel is refluxed for a certain time to generate alumina by the reaction of Equation 1 below to remove oxygen. Alumina is transported from the molten steel to the slag layer through impingement, coalescence, and flotation separation during reflux, but some remain in the molten steel. Nonmetallic inclusions in the molten steel will increase as more aluminum is added, causing a defect in the product. Since it is impossible to completely remove these inclusions, it is important to minimize them, but it is difficult to minimize the oxygen content at the end of decarburization.

Therefore, in recent years, a method of shortening deoxidation time by reducing the oxygen content at the end of decarburization by dividing a small amount of aluminum into molten steel during the initial 4-8 minutes of refining rather than minimizing nonmetallic inclusions has been proposed. have. However, this method has the advantage of shortening the refining time, but there is a problem of suppressing the decarburization reaction by adding aluminum having strong deoxidizing power during the decarburization reaction, and the production of high clean steel using nonmetallic inclusions is still inevitable. Is difficult.

Therefore, the present invention has been made to solve the above problems of the prior art, it is possible to reduce the production cost while effectively improving the cleanliness of molten steel by minimizing the dissolved oxygen after the decarburization operation without disturbing the decarburization operation during vacuum degassing process To provide a method for refining ultra low carbon steel, which has a purpose.

1 is a schematic diagram of a vacuum degassing facility

2 is a graph showing a decrease in the amount of aluminum input according to the addition of

3 is a graph showing the relationship between oxygen content and oxidation degree before deoxidation

Explanation of symbols on the main parts of the drawings

1 ..... ladle 2 ..... molten steel

3 ..... immersion pipe 4 ..... vacuum chamber

The present invention for achieving the above object, in the refining method of refluxing and deoxidation treatment by refluxing molten steel received in the ladle into the vacuum tank of the vacuum degassing equipment, the vacuum tank when the dissolved oxygen amount of the molten steel is 400 ppm or more It is comprised including the addition of 0.09-0.28Kg of a carburizing agent per ton of molten steel in a decarburization process.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is characterized by effectively reducing the amount of deoxidizer added by adding a carbonizer during decarburization to remove unnecessary dissolved oxygen, and according to the present invention, there is no problem in the calcined carbon component.

As described above, the refining of the ultra low carbon steel is first refined in the converter and exited by ladle, and then the reflux tube of the vacuum degassing equipment is deposited on the molten steel received in the ladle, and the pressure in the vacuum chamber is reduced to vacuum the molten steel. Ascending inside the bath to decarburize and deoxidize

Molten steel tapping out of the converter before vacuum degassing process must contain a certain amount of oxygen to make carbon component less than 70ppm. In the early stage of vacuum degassing process, dissolved oxygen is managed to more than 350ppm, but it is often contained more than that. Therefore, since the amount of dissolved oxygen becomes unnecessarily large, a large amount of deoxidizer is required in the deoxidation treatment.

In the present invention, a carbon dioxide is injected into molten steel having an arrival oxygen of 400 ppm or more. In this case, the input amount needs to be appropriately adjusted. When a large amount of the catalyst is added, the oxygen in the molten steel is drastically lowered, but it is disadvantageous in terms of extending the decarburization time, and when the oxygen is too low, the decarburization operation becomes difficult, causing problems in the carbon steel component. If the input amount is small, the effect of minimizing the oxidation inclusions in the molten steel is minimal. In the present invention, in consideration of this, 0.09 to 0.28 kg of a carburizing agent per ton of molten steel is introduced into the vacuum chamber during the decarburization treatment.

Preferably, it is better to divide and add the required amount of carburizing agent at a time than to put at a time. This is because explosion may occur due to rapid CO reaction when a large amount is added at one time. As can be seen in the embodiment, the amount of one-time injection is preferably divided into 10 to 15 kg (0.03 to 0.047 kg per ton of molten steel) at a time of 320 tons of molten steel.

In addition, it is advantageous that the addition time of the catalyst is shortened within 2 to 5 minutes (between 2 to 5 minutes after the start of reflux), which is the initial stage of the decarburization treatment in which the decarburization reaction is actively performed. According to an embodiment of the present invention, the oxygen content is 400 to 450ppm for about 1 minute, 451 to 550ppm for about 2 minutes, 551ppm or more may be added for about 3 minutes.

In the case of adding the charcoal according to the present invention, the change in the amount of aluminum deoxidizer added in the deoxidation process according to the amount of the charcoal input may be confirmed in FIG. 2. In addition, according to the present invention it can be seen in Figure 3 that reducing the amount of dissolved oxygen before deoxidation can obtain a clean steel excellent in quality and cost in terms of less oxidation.

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

EXAMPLE

Oxygen content before vacuum degassing treatment When the 320 tons of molten steel as shown in Table 2 is vacuum degassing as shown in Table 2, the oxygen content before deoxidation treatment, the input amount of deoxidizer during deoxidation treatment, and the content of calcined carbon It is shown in Table 2 below.

division Vacuum deoxidation gas treatment oxygen (ppm) Addition of carburizing agent during decarburization Deoxidation preoxygen (ppm) Decarburization time (min) Carbon before treatment (ppm) Small carbon (ppm) Al input amount in deoxidation (kg) 1 dose (kg) Input cycle (minutes) Input frequency (times) Total input amount (kg) Conventional example One 510 Not carried 350 15 350 31 370 2 460 Not carried 270 16 410 32 330 3 614 Al split injection during decarburization 120kg 280 17 290 47 340 4 455 Al60kg 260 17 380 43 320 5 470 Al70kg 255 18 360 42 320 Comparative Example 6 505 10 0.5 2 20 290 15 380 29 340 Inventive Example a 523 10 0.5 3 30 321 16 350 31 350 b 501 10 0.5 3 30 318 16 380 30 350 c 498 10 0.3 5 50 212 17 360 33 300 d 464 10 0.5 4 40 205 17 390 28 290 e 580 15 0.3 5 70 295 18 300 35 340 f 470 10 0.5 3 30 220 17 420 29 300 g 620 15 0.3 6 90 264 20 280 36 320 h 480 10 0.5 4 40 214 16 400 35 300 i 514 10 0.5 5 50 231 17 370 32 310 j 586 15 0.3 6 80 227 18 300 34 310 Comparative Example 7 723 15 0.3 8 110 298 22 250 39 340 Comparative Example 8 695 15 0.3 7 100 289 22 270 40 340 The lubricating agent starts pouring the molten steel into the vacuum chamber from 2 minutes after the reflux starts.

As shown in Table 2, the conventional examples (1, 2) is somewhat advantageous in terms of decarburization time, but the oxygen content after decarburization (before deoxidation) is high, so that a large amount of deoxidizer is input. In addition, in the case of the prior art (3, 4, 5), the oxygen content after decarburization is low, but the amount of Al added during deoxidation is large, but the amount of Al added as a whole is high, and the decarburization time is relatively long.

On the other hand, in the case of the invention, since a cheaper than Al is used, the cost can be reduced, and the amount of Al can be minimized by adding a certain amount within a range that does not interfere with the carbon steel component. In the case of the comparative examples (6, 7, 8), the amount of aluminum input can be reduced, but the comparative example (6) is less effective and the comparative examples (7, 8) took too much time for decarburization.

As described above, the present invention can produce high-clean steel by effectively reducing the amount of deoxidizer, such as aluminum for deoxidation of molten steel, and has the effect of lowering the manufacturing cost by reducing the deoxidizer.

Claims (2)

In the refining method of the molten steel received in the ladle to reflux in the vacuum chamber of the vacuum degassing equipment, decarburization and deoxidation treatment, A method for refining ultra low carbon steel by introducing a carbonaceous agent during vacuum degassing treatment, wherein when the dissolved oxygen amount before decarburization is 400 ppm or more, 0.09 to 0.28 Kg of carbonaceous agent per ton of molten steel is introduced into the vacuum chamber during decarburization. The method of claim 1, wherein the addition of the charcoal is divided into 0.03 to 0.047 Kg per ton of molten steel at a time during decarburization within 2 to 5 minutes after the start of reflux.