KR100583997B1 - Gas injecting method for improving the steel cleanliness - Google Patents

Abstract

The present invention relates to a blowing method of the gas used in the process of removing the inclusions in the molten steel, the gas is injected into the molten steel to remove the inclusions 120 contained in the molten steel 110 using buoyancy. In a conventional gas blowing method, the gas is blown in a content of 0.008 1 / min-Kg within 1 minute and 30 seconds of the initial blowing process, and the gas is blown in a content of 0.005 1 / min-Kg within 1 minute of the middle stage. And, within 5 minutes of the terminal process characterized in that the gas is blown to the content of 0.002 1 / min-Kg, by adjusting the gas injection amount according to the inclusion content of the molten steel, the removal efficiency and removal speed of the inclusions will be improved In addition, the cleanliness of molten steel is improved.

Steel container, molten steel, inclusions

Description

Gas injecting method for improving the steel cleanliness

1 is a schematic diagram of a state in which a mixture is interposed in molten steel according to a general technique;

2 is a view showing a state in which the cleanliness of the molten steel according to the present invention is improved.

Explanation of symbols on the main parts of the drawings

100: water container 110: molten steel

120: inclusions

The present invention relates to a blowing method of the gas used in the process of removing the inclusions contained in the molten steel, in particular the molten steel that can improve the removal efficiency of the inclusions by changing the blowing amount pattern of various gases injected into the molten steel It relates to a gas blowing method for improving cleanliness.

In general, various inclusions contained in molten steel have a property not to come into contact with molten steel, but have a property of coalescing with each other when colliding with other inclusions.

Therefore, a method of blowing bubbles into the molten steel by using the characteristics of the inclusions or blowing a powder having a volume relatively larger than the inclusions with the bubbles so that the buoyancy of the inclusions is increased to rise to the top of the molten steel.

That is, when inclusions are present in the molten steel, the inclusions are buoyant due to the density difference with the molten steel. At this time, the buoyancy of the inclusion is different depending on the physical properties of the molten steel and the density of the inclusion and the size of the inclusion, and can be obtained through the following equation (1) assuming that the shape of the inclusion is spherical.

*** Ｖ _ｔ = 2R ² (ρ _m -ρ _ｉ ) / 9η --------------------------- (1)

V _t: inclusions injury rate, R: radius of the inclusions, _m ρ: steel density, ρ _i: density of inclusions, η: viscosity of the molten steel

In addition, looking at Equation (1), it can be seen that when the values of all properties are fixed and invariant, the floating velocity (Ｖ _ｔ ) of inclusions in the molten steel is proportional to the square of the inclusion radius (R). .

In this case, the bubbles formed in the molten steel are estimated to have a size of several centimeters or more, and the inclusions in the molten steel have a size of several tens of micrometers. In other words, when the inclusions are present in the molten steel alone, the inclusion radius is very small, so that the inclusions do not rise sufficiently during the treatment time.

That is, the size of the bubble is about 100,000 times larger than the inclusions, and the floating speed is a speed proportional to 100,000 squares by Equation (1), and the floating time of the inclusions corresponds to the inverse of the square of 100,000. As fast as it will be.

By the way, when the gas for separating the inclusions in the molten steel is blown, in the positive aspect, the inclusions have a characteristic that the floating speed is increased and the removal efficiency is proportionally improved. There was a problem.

The reason is, as shown in Figure 1, because the molten steel 110 accommodated in the receiving container 100 and the inclusions 120 floating thereon are mutually reacted, that is, the environment suitable for contaminating the molten steel 110 This leads to the following reactions that contaminate the molten steel.

First, inclusion of inclusions in the molten steel: because the stronger the stirring of the molten steel 110, the stronger the contact between the molten steel and the slag 120 is increased the possibility that a portion of the slag is mixed into the molten steel.

Second, mixing of the refractory into the molten steel: erosion of the refractory occurs during the reaction of the refractory and the molten steel 110 of the container 100 or stirring the molten steel, the eroded refractory is mixed into the molten steel.

Third, reaction with deoxidation component in molten steel: Molten steel 110 reacts with weak deoxidation components (MnO, FeO, etc.) present in inclusions 120 to contaminate molten steel again, and also react with oxygen in the atmosphere. It is because it lubricates molten steel.

Therefore, if the amount of gas blown into the molten steel 110 is increased, the removal efficiency of the inclusions 120 is improved, but since the amount of inclusions is mixed into the molten steel again, the cleanness of the molten steel is ultimately determined by the variable of the gas blowing amount. It can be.

However, since the gas is blown in a constant amount irrespective of the content of the inclusions suspended in the molten steel 110, the removal efficiency of the inclusions 120 is doubtful, and thus there is a problem that the removal speed of the inclusions is increased.

Accordingly, the present invention has been made to solve the problems described above, by adjusting the amount of gas blown according to the amount of inclusions contained in the molten steel, molten steel to improve the removal efficiency and removal speed of the inclusions The purpose is to provide a gas blowing method for improving cleanliness.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a view showing the cleanliness of the molten steel according to the present invention, in the conventional gas blowing method for blowing gas into the molten steel to remove the inclusions 120 contained in the molten steel 110 using buoyancy, The gas is blown with 0.008 1 / min-Kg within 1 minute 30 seconds of the initial blowing process, and the gas is blown with 0.005 1 / min-Kg within 1 minute of the middle blowing process. Characterized in that the blowing gas to the content of 0.002 1 / min-Kg.

First, through the formulas (2) and (3), the removal rate (Κ) of the inclusions 120 increases as the amount of gas supplied increases, but on the contrary, the incorporation rate of gas into the molten steel increases relatively. The relation (2) is expressed as follows.

*** ド Ｏ / ｄｔ = -ΚＯ ------------------------------------ (2)

O is the value obtained by substituting the amount of oxygen contained in the inclusions with the concentration compared to the amount of molten steel when the whole inclusion is regarded as an oxide (hereinafter referred to as T.O value); .

*** dO / d == (-) ----------------------------------- (3)

ｆ (Ｑ): It is a constant determined according to the flow rate of blown gas, ie, a constant of the degree of inclusions in the molten steel.

In addition, the relationship (4) can be derived using the relationship (2, 3) to obtain the removal rate (k) of the inclusions in consideration of the dynamic equilibrium of the inclusions.

*** (dＯ / ｄｔ) net = -ΚＯ + ｆ (Ｑ) ----------------------- (4)

Equation (4) is used as a differential equation over time, and the following equation (5) can be obtained by using the solution of a general differential equation.

*** Ｏ = (Ｏ _i -ｆ (Ｑ) / Κ) * ｅ ^-Κｔ + ｆ (Ｑ) / Κ ----------------- (5)

Here, looking at Equation (5), the right side term 1 shows the behavior of the value of T.O, and the right side term 2 shows the removal system of the value of T.O when the time passes indefinitely. In other words, looking at the right side, it can be seen that the final T.O value is almost unchanged no matter how large the removal rate Κ of the inclusions is.

However, the removal rate (Κ) of the inclusions and the degree of inflow (ｆ) of the inclusions increases as the flow rate increases, but as the flow rate increases, the inclusions increase as the flow rate increases. The removal system of the right side (paragraph 2) was found to be high.

On the other hand, by using the relational expressions (2 to 5), the apparent removal rate (Κ ') of the inclusions at each flow rate can be obtained, and the value is obtained through the relational expression of dO _net / 6, 7) can be obtained.

*** ド Ｏ _net / ｄｔ = -ΚＯ + ｆ (Ｑ) =-(Κ-ｆ (Ｑ) / Ｏ) ・ Ｏ = -Κ'Ｏ --- (6)

*** ∴ Κ '= Κ-ｆ (Ｑ) / Ｏ ----------------------------------- (7)

 Here, looking at Equation (6), even under the same stirring conditions, it can be seen that the removal rate (Κ) of the same inclusions is not always maintained, and the removal rate of the inclusions depends on the T.O value. That is, the removal rate (Κ) of the inclusions shown in Equation (6) is relatively large compared to ｆ (Ｑ) / O when the gas supply amount (O) increases.

On the other hand, when the value of T.O is lowered, the value of k (O) / O is relatively increased, and the apparent removal rate (k ') of the inclusions appears to decrease. That is, in the steelmaking process in which slag and molten steel coexist, the apparent removal rate Κ 'of inclusions in the molten steel is not a constant but a value that varies depending on the value of T.O.

This is because, as in equation (7), the inclusion removal rate Κ and the T.O value are constant, while the gas supply amount O located in the denominator is changed. In addition, when the stirring force of molten steel is strong, the removal rate (k) of an interference | inclusion normally increases, and at the same time, the kV value which is the grade of inclusions also increases.

When the gas flow rate is high, for example, when the T.O value is high, the apparent removal rate (Κ ') of the inclusions is high, and when the T.O value is low, the apparent removal rate (Κ') by the inclusions is low. Can be.

However, when the flow rate was low, it was found that the T.O value and the inclusion apparent removal rate (Κ ') were inversely proportional. Therefore, in order to improve the removal efficiency of the inclusions, the optimum apparent removal rate (K ′) must be maintained. Therefore, the task of obtaining the K 'value of the optimum condition according to the stepwise change of the T.O value should be determined.

(Example)

First, as shown in Table 1, the flow rate of gas was divided into eight stages, blown into the molten steel, and a molten steel sample was taken every 30 seconds. Thereafter, the collected samples were processed, and the T.O values in the steel were measured using a N ₂ / O ₂ simultaneous analyzer manufactured by LECO Corporation.

Table 1 Gas Flow Rate

case A B C D E F G H Blown flow rate (1 / Min-Kg) 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

Each T.O value was obtained for each blown flow rate (A to H) as shown in Table 1, and then the apparent removal rate (Κ ') of the inclusions was obtained using Equation (8).

Κ '=-1 / オ ド Ｏ / ｄｔ ------------------------------ (8)

Of course, the method of calculating the apparent removal rate Κ ′ of the inclusions is based on the T.O value at each step, the difference between the T.O at the previous step and the step, and the time difference. Obtained by typing. Subsequently, the relationship between the apparent removal rate (K ') and T.O of the inclusions was analyzed in the form of Κ' = a + b / T.O for each step, and the values of a and b were determined as shown in Table 3. It was.

{Table 2} a and b for each flow

case A B C D E F G H a 18 25 32 35 45 51 67 68 b 0.33 0.44 0.55 0.60 0.73 0.82 0.90 1.04

Here, as shown in Table 2, it is understood that the cleanliness of the molten steel depends on the value of K 'for each T.O, so that it is preferable to select the flow rate at which the value of K' is the highest.

Usually, the molten steel deoxidized from the converter is promoted homogenization by strong stirring action during the tapping, and the removal work of the inclusion occurs. Therefore, the T.O value of the molten steel is about 90 to 120 ppm, and the pattern was set based on this.

At this time, assuming that the T.O value of the initial state was an average of 110 ppm, the gas was blown at the flow rate value having the highest Κ 'value in each step, and the highest Κ' value was selected as follows.

(1). At 110 ppm, the gas is blown at the flow rate with the highest Κ 'value.

(2) After the next 6 seconds, the initial value is set to the value of 6 seconds and the elapsed time is 6 seconds, and the T.O value is compared by applying the Κ 'value of H and G Κ' value shown in Equation (5). do.

(3). When Κ 'of H is applied, if the value of T.O is low, the process of (2) is repeated after 6 seconds.

(4). If G's value is low (2) and (3), repeat the process and compare with F.

(5). Repeat the steps (2) and (3) in the same direction as E → A.

As a result of determining the pattern having the lowest flow rate value through the method (1) to (5), the results of Table 3 were obtained.

{Table 3}

division H G F E D C B A Retention time (seconds) 12 30 42 18 18 18 24 continue Ｔ.Ｏ 110 101.8 87.3 75.9 72.9 70.6 68.8 67.0

Table 3 is the result of considering the minimum time unit and the flow rate unit that can control the equipment in one embodiment.
However, as shown in Table 3, the results of the tests performed by dividing each flow value into very small intervals are effective in improving the removal efficiency of inclusions. However, practical problems, for example, if the interval is too small, it is difficult to control during the operation process and work process. Since this is inconvenient, the patterns were set at intervals as shown in Table 4.

{Table 4}

flux 0.008 0.005 0.002 Holding time (1 / min-Kg) 1 minute 30 seconds 1 minute 5 minutes

Table 4 shows the results of recalculation applying the actual operating conditions.
As shown in Table 4, the molten steel 100 was taken at intervals of one minute, and the T.O value was analyzed by the above-described method. The T.O value was lower than that of the H method, and it was found that the T.O value was reached much faster than the A method.

As described above, according to the gas blowing method for improving the cleanliness of molten steel according to the present invention, by adjusting the gas blowing amount according to the inclusion content of the molten steel, not only the removal efficiency and removal speed of the inclusions are improved, but also Cleanliness is to improve the effect.

Claims (1)

In the conventional gas blowing method of blowing gas into the molten steel to remove the inclusions 120 contained in the molten steel 110 by using buoyancy, The gas is blown with 0.008 1 / min-Kg within 1 minute 30 seconds of the initial blowing process, and the gas is blown with 0.005 1 / min-Kg within 1 minute of the middle blowing process. A gas blowing method for improving the cleanliness of molten steel, characterized in that the gas blowing in a content of 0.002 1 / min-Kg.

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