KR100398379B1 - A method for decarburizing steel melts in rh vaccum degassing equipment - Google Patents

Abstract

The present invention relates to a decarburization method of molten steel for rapidly producing ultra low carbon steel in the steelmaking process, the purpose of which is easy to apply to the RH facility, while preventing refractory erosion of the vacuum tank as well as effectively promote the decarburization reaction of the molten steel This is to significantly reduce the decarburization time of molten steel.

The present invention for achieving the above object is a method of performing decarburization by refluxing molten steel refined to 0.035% by weight of carbon in the converter blowdown through the ascending and descending pipes of the vacuum degassing equipment, the rising of the vacuum degassing apparatus The degassing method of molten steel by the vacuum degassing apparatus which comprises inserting a double pipe to one side of the pipe, blowing oxygen gas through the inner pipe of the double pipe, and blowing an inert gas to the outside of the double pipe. Make a point.

Description

Method for decarburization of molten steel by vacuum degassing facility {A METHOD FOR DECARBURIZING STEEL MELTS IN RH VACCUM DEGASSING EQUIPMENT}

The present invention relates to a method for decarburizing molten steel for rapidly producing ultra low carbon steel in a steelmaking process.

In the steelmaking process, molten iron produced from the blast furnace is desulfurized or dephosphorized and charged into the converter to manufacture molten steel by oxyfuel blowing. The molten steel produced contains about 0.035% by weight or more of carbon (hereinafter, only `% '), and oxygen contains about 0.04%. Therefore, in order to manufacture molten steel having a carbon content of less than 0.035%, in particular molten steel containing less than 0.005% of carbon must go through a separate process.

In general, a vacuum degassing facility (hereinafter referred to as 'RH facility') as shown in FIG. 1 is used to manufacture carbon content present in molten steel to about 0.005% or less. That is, in the molten steel decarburization operation in the RH facility as shown in FIG. 1, the vacuum chamber 1 is allowed to rest on the ladle 3, and then the molten steel 5 is formed through the rising tube 2a and the lower tube 2b of the vacuum chamber. While refluxing, the inert gas is blown from the gas blowing pipe 4 provided on one side of the rising pipe 2a, and a method of encouraging the reaction of carbon and oxygen under vacuum is used. At this time, the reaction of carbon and oxygen in the molten steel is represented by the reaction formula (1).

[C] + [O] = CO (g), K = P _CO / (a _C aa _O )

Looking at the reaction equilibrium constant K of Scheme 1, in order for the reaction to occur, the concentration of carbon and oxygen in the molten steel or the partial pressure of carbon monoxide, the reaction product, must be low. By lowering the partial pressure of carbon monoxide based on this principle, molten steel decarburization proceeds under vacuum of the RH facility. However, the decarburization operation of molten steel as shown in FIG. 1 merely uses a method of promoting the reaction of carbon and oxygen under vacuum.

On the other hand, as shown in Figure 1 there are generally three places where the decarburization reaction occurs in the RH. That is, the interface between the molten steel and the vacuum gas phase, the surface of the gas phase introduced to reflux the molten steel and the inside of the molten steel. The reaction rate at the interface with the vacuum gas phase in the reaction zone is determined only by how fast carbon and oxygen are supplied to the molten steel surface, and the reaction at the interface with the reflux gas phase is blown through the riser in FIG. It is determined by the amount of inert gas for reflux and the moving speed of carbon and oxygen to the reflux gas phase interface. In addition, the reaction occurring inside the molten steel increases the reaction rate as the concentration of carbon and oxygen present in the molten steel increases. That is, the decarburization rate of the molten steel by the RH facility is determined by the overall reaction factor, which can be briefly represented by Scheme 2.

d [C] / dt = k [C] → [C] = [C] o · exp (-kt)

Where d [C] / dt: decarburization rate of molten steel

[C]: Carbon content in molten steel at present

[C] _o : initial carbon content

k: molten steel decarburization rate constant

t: processing time

Looking at Reaction Equation 2, in order to promote the decarburization rate of the molten steel can be increased by increasing the molten steel decarburization rate constant k value. The superiority of the decarburization speed can be determined by observing the decarburization rate constant k value in each case. The rapid decarburization speed means a shorter decarburization time, which is a great advantage in the actual industry.

In this regard, a new method of increasing the flow rate of reflux gas, which is the source of force for moving molten steel, and increasing the concentration of oxygen in molten steel has been studied in order to speed up the movement of carbon and oxygen in molten steel. That is, in recent years in refining ultra low carbon molten steel, in addition to the decarburization operation of molten steel as shown in FIG. 1, oxygen is blown from the hot water surface of the molten steel 5 using the upper lance 6 as shown in FIG. 2 to promote the reaction between carbon and oxygen. The method of making it use, etc. are used. However, in the decarburization method of molten steel by oxygen deodorization as shown in Fig. 2, the lance and the hole must be raised and lowered after the lance 6 is allowed to pass through the upper portion of the vacuum chamber 3. Since the sealing of the liver is considerably difficult, and oxygen is blown from the upper part to impact the molten steel hot water surface, the hot water surface may be deeply recessed to damage the refractory material of the bottom tank.

The present invention provides a decarburization method of molten steel that can facilitate the decarburization reaction of molten steel while preventing refractory erosion of the vacuum bath as well as easy application to RH facilities unlike the decarburization operation of the conventional ultra low carbon molten steel. There is a purpose.

1 is a structural diagram of a vacuum degassing apparatus for explaining a conventional molten steel decarburization method

Figure 2 is a structural diagram of a vacuum degassing facility for explaining another conventional molten steel decarburization method

Figure 3a is a structural diagram of a vacuum degassing facility for explaining the molten steel decarburization method of the present invention

FIG. 3B is a detailed view of portion “A” of FIG. 3A

* Explanation of symbols for the main parts of the drawings *

1 ... vacuum chamber, 2a ... riser, 2b ... downcomer,

3 ... ladle, 4 ... gas blown pipe, 5 ... molten steel,

6 ... lance, 7 ... double pipe, 7a ... appearance,

7b ... Appearance

The present invention for achieving the above object in the method for performing decarburization by refluxing the molten steel refined to 0.035% by weight in the converter blown through the ascending and descending pipes of the vacuum degassing equipment,

The molten steel by vacuum degassing equipment comprising a double pipe is inserted into one side of the rising pipe of the vacuum degassing apparatus, and the oxygen gas is blown through the inner pipe of the double pipe and the inert gas is blown into the outer pipe. It relates to a decarburization method.

First, the present invention will be described in detail through the RH facility of FIG.

Figure 3a shows a structural diagram of the RH facility for explaining the molten steel decarburization operation of the present invention, Figure 3b is a detailed view of the portion A. As shown in FIG. 3, the present invention provides a double tube 7 on one side of the rising tube 2a of the vacuum chamber 1 that is settled on the ladle 3 so that the appearance 7a of the double tube 7 is provided. The furnace is characterized in that the inert gas is blown while the inner pipe 7b is blown with oxygen to carry out the decarburization operation. That is, the present invention replaces the reflux gas with oxygen gas and inert gas by using the double pipe 7 instead of the conventional single pipe type gas blowing pipe 4.

The inert gas blown through the appearance of the double pipe according to the present invention performs a function of a cooling gas to prevent the nozzle from being damaged by the heat of reaction between oxygen and molten steel and the heat of reaction of oxygen and carbon, thereby refluxing the molten steel. It works.

In addition, the oxygen blown through the inner tube of the double pipe increases the concentration of oxygen in the molten steel and increases the degree of reflux of the molten steel using carbon monoxide gas generated by the reaction as shown in Equation 3.

2 [C] + O ₂ = 2CO

That is, as shown in Reaction Equation 3, when 1 mole of oxygen gas reacts, 2 moles of carbon monoxide gas is generated, so that the amount of gas generated is doubled, thereby increasing the volume of the gas to be injected, thereby increasing the reflux rate of the molten steel and To increase the speed of carbon

Of course, as a device for performing a function similar to the present invention, there is an oxygen blowing means in which a nozzle is located on one side of the vacuum tank riser of FIG. 1, but the means is used for the purpose of raising the temperature of molten steel using a reaction between aluminum and the blown oxygen. In addition, at this time, the blown oxygen escapes to the molten steel bath at the same time as blown, and increases the oxygen concentration in the molten steel or the effect on the reflux of the molten steel. In particular, the double pipe according to the present invention has the advantage that the decarburization rate of the molten steel can be easily installed in the vacuum tank above all, compared to the conventional oxygen phase lance.

On the other hand, the double tube is inserted into the vacuum chamber is necessary to design appropriate for each vacuum chamber so that there is no attachment. For example, in the present invention, the inner tube of the double tube is about 1.5 ~ 2mm in the inner diameter, the outer diameter of about 5.5 ~ 6mm is suitable, but not necessarily limited thereto.

In addition, the flow rate of the inert gas blown in the outer appearance is in the range of 0.2 ~ 0.3Nm 3 / min-molten steel, the flow rate of oxygen blown in the inner pipe is in the range of 0.3 ~ 0.4Nm 3 / min-molten steel 1 ton Blowing in is preferable.

Under such conditions, decarburization operation of molten steel can easily control the carbon content in the molten steel to 0.02% or less, and can promote the reaction of carbon and oxygen under vacuum, thereby greatly reducing the decarburization treatment time.

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

Example 1

The molten steel was refluxed using a 330 ton capacity RH facility while a double tube was inserted into one side of the ascending tube of the RH facility to inject oxygen into the inner tube and argon gas to the outside to decarburize the molten steel. The inner tube of the double tube used in the present embodiment was 1.2mm in thickness, 2mm in diameter, the appearance of the thickness was 1.5mm, 6mm in diameter was used, respectively, was blown at a pressure of 3.5atm, 3.0atm. In addition, the decarburization time of the molten steel was carried out for about 13 minutes, the flow rate of each argon gas and oxygen and the composition before and after the decarburization treatment of molten steel is shown in Table 1.

division Comparative Example 1 Inventive Example 1 Inventive Example 2 Comparative Example 2 Gas flow rate (N㎥ / min-molten steel 1 ton) argon 0.4 0.3 0.2 0.1 Oxygen 0.2 0.3 0.4 0.5 Molten steel volume (ton) 326 325 327 324 Before decarburization [% C] 0.037 0.035 0.038 0.036 [% O] 0.038 0.039 0.037 0.038 Temperature (℃) 1590 1587 1589 1588 After decarburization [% C] 0.004 0.0021 0.0023 0.0028 [% O] 0.025 0.032 0.034 0.042 Temperature (℃) 1575 1582 1579 1580 Reaction constant (k) 0.17 0.22 0.21 0.20

As shown in Table 1, Inventive Example 1 is the best in the decarburization behavior in the treatment time, temperature decrease amount, etc., and also in the case of Inventive Example 2 is not significantly inferior to Inventive Example 1.

On the other hand, in Comparative Example 1, the decarburization capacity and reaction rate are somewhat slow, and in Comparative Example 2, the decarburization capacity is excellent, but the oxygen concentration in molten steel is high after treatment, and an excessive amount of deoxidizer is required. The following was not suitable.

Example 2

In order to compare with the conventional method, molten steel decarburization was performed by using a general RH facility (former example 1) and an oxygen phase lance (former example 2). At this time, decarburization was performed for 13 minutes each. Table 2 shows the decarburization degree of the molten steel treated according to each method.

division Conventional Example 1 Conventional Example 2 Inventive Example 1 Gas flow rate (N㎥ / min-molten steel 1 ton) argon 0.3 - 0.2 Oxygen - 0.5 0.4 Molten steel volume (ton) 335 328 325 Before decarburization [% C] 0.038 0.036 0.035 [% O] 0.043 0.038 0.039 Temperature (℃) 1590 1593 1587 After decarburization [% C] 0.0037 0.0022 0.0021 Temperature (℃) 1565 1580 1582 Reaction constant (k) 0.19 0.22 0.22

As shown in Table 2, in the present invention, the decarburization rate constant k of the molten steel, as well as the decarburization capacity of the molten steel while maintaining the same level as the decarburization method (conventional example 2) by the conventional oxygen phase lance rather than the amount of temperature reduction of the molten steel during treatment It can be seen that less.

As such, in the case of the present invention, the high decarburization rate means that the decarburization time of molten steel can be greatly reduced. In fact, molten steel that required decarburization for about 13 minutes could reduce the decarburization time to about 1/4.

As described above, the decarburization treatment method of the present invention is not only easy to apply to the RH facility but also can effectively promote the decarburization reaction rate of molten steel while preventing refractory erosion of the vacuum chamber, thereby greatly reducing the decarburization treatment time of the molten steel as a whole. There is a very useful effect of greatly improving the decarburization in the conventional RH facility.

Claims (1)

In the method of reflowing molten steel refined to 0.035% by weight of carbon in the converter blown through the ascending and descending pipes of the vacuum degassing facility, A double pipe is inserted into one side of the rising pipe of the vacuum degassing apparatus, and oxygen is blown in the range of 0.3 to 0.4 Nm 3 / min-molten steel through the inner pipe of the double pipe, and inert gas is 0.2 to 2 in appearance. Method for decarburization of molten steel by vacuum degassing equipment blowing in the range of 0.3N㎥ / min