KR20070059747A - Method for refining molten steel in converter - Google Patents

Abstract

A method for refining molten steel in a converter is provided to prevent air pollution and facility damage due to the slopping and safely operate the converter by preventing slopping from being generated, and stabilize the refining process and reduce the refining time by varying the oxygen blowing rate and the lance height in the early stage of refining. A method for refining molten steel in a converter comprises: a step(S10) of charging iron scrap and hot metal into the converter; a first blowing step(20) of preferentially removing Si in hot metal to prevent slopping from being generated; a step(S30) of discharging slag generated after performing the desiliconizing blowing; a second blowing step(S40) of continuously performing decarburizing blowing of the slag discharged hot metal; a step(S50) of performing a tapping process of tilting a blowing operated finished converter to send molten steel to a ladle; a step(S60) of performing a slag coating process for protecting the body of the converter after completing the tapping process; and a step(S70) of performing a slag discharging process of tilting the converter to an angle of 140 to 180 degrees of an angle of the charging side to discharge residual slag into a container called as a slag pan. The first blowing step is performed by reducing the oxygen blowing rate to 28,500 to 31,500 Nm^3/hr at a predetermined changing time point after maintaining an oxygen blowing rate in the early blowing stage to 38,000 to 42,000 Nm^3/hr.

Description

Method for Refining Molten Steel in Converter}

1 is a process progress diagram of the converter refining method according to the present invention.

Figure 2 is a graph showing the exhaust gas content according to the progress of the blow during the first blow.

3 is a schematic cross-sectional view and a plan view showing a blow-in operation situation in the case of a relatively low flow rate and low lance height.

4 is a schematic cross-sectional view and a plan view showing a blow-in operation situation in the case where the flow rate is relatively high and the lance height is high.

5 is a schematic view showing the blown pattern of a comparative example according to the prior art.

6 is a schematic diagram showing the blowing pattern of the embodiment according to the present invention;

<Explanation of symbols for the main parts of the drawings>

10: converter 20: lance

30: molten iron 40: slag

50: scrap metal

The present invention relates to a converter refining method, and more particularly to a converter refining method that can prevent the slipping (shortening) and shorten the refining time.

Generally, the steelmaking process proceeds in the order of molten iron pretreatment, converter refining, secondary refining, and continuous casting.

The converter refining process removes carbon and impurity elements from molten iron in the form of oxides of CO gas or slag by blowing molten iron into the converter and blowing high-purity oxygen gas through the lance. It is called molten steel.

The impurity element in the molten iron during the blowing operation of the converter is subjected to the oxidation reaction as shown in the reaction formula 1 to 5 and the pure oxygen gas blown.

[C] + 1/2 O ₂ = CO (g)

[Si] + O ₂ = SiO ₂

[Mn] + 1/2 O ₂ = MnO

[Fe] + 1/2 O ₂ = FeO

2 [P] + 5/2 O ₂ = P ₂ O ₅

According to Scheme 1, carbon is oxidized to carbon monoxide (CO) to be removed in the gas phase, and Schemes 2 to 5 are present in the slag layer while the secondary materials introduced during the converter operation are recycled.

The slag layer thus formed actively reacts with the molten iron by the stirring action by the collision energy of low odor gas (N ₂ , Ar) and pure oxygen to stably remove impurities in the molten iron.

Carbon monoxide produced by the reaction of Scheme 1, in particular, a very small bubble (foam) size and fine carbon monoxide is not easily released to the outside through the slag layer is stagnant in the upper part of the molten iron and the slag layer and then suddenly rapidly slag and molten iron Pushing upwards, that is, slag foaming may occur. In addition, the generation of carbon monoxide gas can cause the slag and molten iron to be ejected out of the converter during the blow, which is called the "slopping". This phenomenon is affected by the amount and composition of the slag, the molten iron condition, the rate of carbon monoxide generation and the size of the generated gas. For example, when the Si component in the molten iron is 0.65% or more, a lot of heat of reaction is generated initially, thereby accelerating the quicklime melting rate. That is, a large amount of liquid slag is formed from the initial stage, and thus, when the 30% of the blowing progress is performed when the decarburization reaction is vigorous, a large amount of slag may be ejected out of the furnace. Sloping that occurs during the conversion of converters not only results in the loss of valuable metal, iron, but is also very dangerous for operational safety and can cause serious air pollution.

Therefore, many studies have been conducted to prevent the slipping phenomenon in the refining process. To this end, conventionally, by injecting oxygen into the molten iron charged into the converter proceeds to the first blow to remove the Si, after the slag is excised and the slag is excised in accordance with the Si content of the molten iron to increase the transmission flow rate Disclosed is a refining method of advancing secondary blowing. Here, in the initial stage of refining, the flow rate was relatively low so that the decarburization reaction did not occur and the lance height was lowered. However, in the conventional refining process, due to the low flow rate and the low lance height, the scrap metal charged into the converter may not be completely dissolved, which may make the slag difficult to be discharged and cause the sling due to the late refining failure. . In addition, there is a disadvantage that the refining process takes a long time due to the disadvantage of the initial slag refining.

The present invention is to solve the above problems, an object of the present invention is to provide a converter refining method that can prevent the occurrence of the slope to prevent air pollution and equipment burnout caused by the slope and to promote the operation safety.

In particular, it is an object of the present invention to provide a converter refining method capable of facilitating the dissolution of scrap metal to stabilize the refining process, promoting the initial goods, and shortening the refining time by changing the flow rate and lance height of the initial refining. It is done.

The present invention, in the converter refining method in order to achieve the above object, the first blowing step of the desulfurization treatment of molten iron, the step of excluding the de-siliconized slag and the second blowing process of decarburizing the molten iron is slag-exposed includes, and a converter refining, comprising a step of said primary blow step is blown while maintaining the initial Songshan flow rate 38000Nm ³ / hr to 42000Nm ³ / hr 28500Nm ³ / hr to 31500Nm reduced to ³ / hr to a predetermined change point for Provide a method.

The first blowing step is characterized in that the initial injection lance height is maintained at 2200mm and changed to 1800mm at the time of the change.

The change point is a time when the total amount of oxygen blown into the converter is 855 to 945 Nm ³ when the Si content in the molten iron is 1.0% or less, and is blown into the converter when the Si content in the molten iron is 1.01 to 1.5%. When the total amount of oxygen blown is 997.5 to 1102.5Nm ³ , and the Si content in the molten iron is 1.51 to 2.0%, the total amount of oxygen blown into the converter may be characterized as a point of time of 1140 to 1260Nm ³ .

The change point is 6% of the blowing time when the Si content in the molten iron is 1.0% or less, and 7% of the blowing time when the Si content in the molten iron is 1.01 to 1.5%, and the Si content of the molten iron is 1.51 to 2.0. In the case of%, it can be characterized in that 8% of the time of blowing.

In the step of excluding the desulfurized slag, the time point of blowing the slag may be changed according to the Si content in the molten iron.

The second blowing step, characterized in that the slag is excised in the molten iron is changed in accordance with the Si content in the molten iron in step by step to increase the flow rate and blow.

Hereinafter, the converter refining method according to the present invention with reference to the accompanying drawings will be described in detail.

The converter refining operation is carried out in the order of charging operation, blowing operation, tapping operation and exclusion operation, Figure 1 shows the process progress of the converter refining method according to the present invention.

First, the scrap iron and molten iron is charged into the converter (S10).

Injecting a high-pressure oxygen gas into the converter to blow at a high temperature (S20 ~ S40). The present invention after the first blow (S20) to remove the Si in the molten iron in order to prevent the sling, that is, desulfurization blow, after the slag generated at this time (S30), the molten iron is slag-excluded To continuously proceed to the second blow (S40), that is, decarburization blow. A tapping operation (S50) is performed in which a molten steel is discharged to a ladle by tilting a converter after finishing the drilling work. After finishing the tapping, the slag coating (S60) work is performed to protect the furnace body, and the remaining slag is carried out to the container called slag pan (S70) by tilting the converter to 140 degrees to 180 degrees on the charging side. do.

In general, since Si has a high affinity with oxygen, it is removed before other impurities during converter refining. Si in the molten iron forms SiO ₂ by oxygen blown during converter refining. As the SiO ₂ content increases, the slag viscosity rises, and since the generated CO gas does not escape the slag layer, the slag layer swells as a whole and the likelihood of occurrence of slopeing increases. Therefore, it is preferable to pretreat the desulfurization treatment before the refining of the converter and to exclude the slag before the decarburization reaction occurs. Next, decarburization is performed while increasing the flow rate in the slag-excluded molten iron. This prevents the occurrence of slopes in the converter.

The present invention sets the blowing pattern of the optimum feed flow rate and lance height in consideration of the desulfurization and decarburization reaction, slope and the like during the blowing operation. In particular, compared to the existing blow pattern to improve efficiency by changing the supply flow rate and the lance height at the beginning of the first blow. Here, the time point of blowing indicates the time point (%) of the total blow in progress which combined the first blow and the second blow.

Figure 5 is a schematic diagram showing the blowing pattern of the comparative example according to the prior art, Figure 6 is a schematic diagram showing the blowing pattern of the embodiment according to the present invention.

Referring to the drawings, the comparative example started the blow job with a feed rate of 30000Nm ³ / hr and maintained up to 20% at the time of the blow when the first blow is generally completed, and increased the feed rate in step after slag exclusion. In addition, the lance height was maintained at 1800 mm at the beginning of the blow, and the slag was removed and changed to 2000 mm at 40-50% of the blow point in progress of the second blow. Here, the reason for starting with a relatively low flow rate and low lance height at the beginning of the blow, may be caused by a sharp denitrification and decarburization reaction due to excessive flow rate at the beginning of the blow, or due to the increase in the surface area as the lance height increases This is to prevent the slope.

On the other hand, this embodiment is the primary blow when 40000Nm ³ / the Songshan flow of hr start blowing operations while in progress to reduce the 30000Nm ³ / hr at a predetermined changing time, the blow point with the slag excluded and the secondary start of the blow It was increased to 400Nm ³ / hr in 20% and then increased the flow rate step by step. In addition, while maintaining the lance height of 2200mm at the time of the first blow, after changing to 1800mm at a predetermined change point, the slag was excluded and changed to 2000mm at 40-50% of the time of the ongoing blow of the second blow. Compared with the conventional blow pattern mentioned above, this increases the flow rate and maintains the lance height relatively at the beginning of the first blow, thereby promoting the desulfurization reaction to shorten the first blow time, and at a predetermined point of change By reducing the feed rate and lowering the lance height, the desulfurization and decarburization reactions can be controlled simultaneously.

As described above, the present invention is advantageous in dissolving scrap metal at the initial stage of the blowing process and the desulfurization time may be shortened by changing the flow rate and the lance height at the beginning of the blowing process. If this is described in more detail as follows.

3 is a schematic cross-sectional view and a plan view showing the situation of the drilling work when the supply flow rate is relatively low and the lance height is low, Figure 4 is a schematic cross-sectional view showing a drilling operation situation when the flow rate is relatively high and the lance height is high And plan view.

Referring to the drawings, high-pressure oxygen is blown into the molten iron 30, the slag 40, and the scrap iron 50 in the converter 10 through the lance 20. In this case, when the flow rate is relatively low and the lance height is low, the scrap metal 50 may not be completely dissolved because the diameter (A) of the firing point is narrow and the depth (B) of the cavity is small. The disadvantage is that it takes a long time. On the other hand, as the flow rate increases and the lance height increases, the diameter (A) of the firing point becomes wider and the depth (B) of the cavity becomes deeper, so that the surface area can be increased to improve the solubility of the scrap metal 50 and to improve the initial goods. Can be promoted. Accordingly, there is an effect that can shorten the process time.

Therefore, the present invention maintains the initial delivery flow rate during the first blow to 38000Nm ³ / hr to 42000Nm ³ / hr, and at a predetermined change point to reduce to 28500Nm ³ / hr to 31500Nm ³ / hr, the initial blow lance height to 2200mm It is preferable to change the length to 1800 mm at the time of the change.

The predetermined change time point for changing the delivery flow rate and the lance height is set according to the Si content in the molten iron as shown in Table 1 below.

Referring to Table 1, when the Si content in the molten iron is 1.0% or less, it is changed to 6% at the time of blowing, and when the Si content in the molten iron is greater than 1.0 and 1.5% or less, it is changed to 7% at the blowing time, and the Si content in the molten iron When it is larger than 1.5 and 2.0% or less, it is preferable to change to 8% at the time of blowing. For example, if the Si content in the molten iron is 1.2%, the while maintaining Songshan flow to blow initially 40000Nm ³ / hr reduced by 30000Nm ³ / hr to the blow point of 7%, likewise while keeping the lance height to 2200mm blowing time Continue to 7% to 1800mm.

The amount of oxygen blown in Table 1 represents the total amount of oxygen blown to the converter from the start of the blow to the change point, and increases for the desulfurization reaction as the Si content in the molten iron increases. Therefore, as the Si content in the molten iron increases, a large amount of oxygen blowing is required, so that the time to proceed with a relatively high flow rate is long, and the change point for reducing the flux rate is delayed.

Figure 2 is a graph showing the exhaust gas content according to the progress of the blow during the first blow, showing the results of the blow if the Si content in the molten iron is 0.70%. Referring to the drawing, the unreacted oxygen is not seen after the initial stage of blowing, and the degassing reaction and the decarburization reaction occur simultaneously after 3 minutes of blowing, and thus the CO gas content is gradually increased. Therefore, in the initial stage of the first blow process where only the desulfurization reaction proceeds, decarburization reaction is less likely to occur even if the flow rate is increased and the lance height is increased, as in the above-described embodiment. By changing the height of the lance to a low level.

After carrying out the primary blow to preferentially remove Si in the molten iron with the blow pattern as described above, the slag generated during the desilification treatment is excluded because it may cause the occurrence of the slope.

Here, the slag exclusion point is changed according to the Si content in the molten iron.

Since the amount of oxygen blown for the desulfurization reaction increases as the Si content in the molten iron increases, the timing at which the desulfurization treatment, that is, the primary blowing is completed, is delayed. Therefore, as shown in Table 2, the time point to exclude the slag after the first blow depending on the Si content in the molten iron.

In addition, after the slag is excluded, the second blow, that is, decarburization is performed, while increasing the flow rate in step to the molten iron in which the slag is excised. Here, as described above, since the slag exclusion point varies according to the Si content in the molten iron, the point of time of changing the delivery flow rate step by step during the decarburization process may vary slightly.

Referring to Table 3, it can be seen that the blowing pattern is changed during the decarburization treatment according to the Si content in the molten iron. The same progresses when the Si content in the molten iron is 1.20% or less. Table 3 shows an example of the second blowing pattern during the converter operation, the delivery flow rate is not limited to this may be changed according to the process variables.

As described above, the present invention can prevent the occurrence of the slope by preventing the generation of the slope by preventing the decarburization treatment and the decarburization treatment after the slag excretion, it is possible to improve the operation safety.

In addition, by increasing the lance height at the beginning of the desulfurization process and increasing the flow rate, it is possible to stabilize the refining process by facilitating the dissolution of scrap metal, and to accelerate the initial goods to shorten the refining time and improve productivity. .

As mentioned above, although this invention was demonstrated in detail using the preferable Example, the scope of the present invention is not limited to a specific Example and should be interpreted by the attached Claim. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

According to the present invention, in the refining process, the decarburization treatment and the decarburization treatment after the slag removal can prevent the occurrence of the slope, thereby preventing the air pollution and the equipment burnout caused by the slope, and the operation safety.

In particular, the present invention by increasing the lance height in the early stage of the desulfurization treatment and increase the flow rate, it is possible to stabilize the refining process by facilitating the dissolution of scrap metal, promote the initial goods to shorten the refining time and productivity There is an effect that can be improved.

Claims (6)

In the converter refining method, A first blowing step of desulfurizing the molten iron; Excluding the desulfurized slag; And It includes a secondary blowing step of decarburizing the slag is excreted molten iron, The primary blow step is blown converter refining method of the initial flow rate Songshan characterized by 38000Nm ³ / hr to 42000Nm while maintaining the ³ / hr reduced 28500Nm ³ / hr to 31500Nm ³ / hr at a predetermined changing time. The method according to claim 1, The first blowing step, The converter refining method, characterized in that to maintain the initial lance height to 2200mm, and to change to 1800mm at the time of the change. The method according to claim 1 or 2, The change time point, When the content of Si in the molten iron is 1.0% or less, the total amount of oxygen blown into the converter is 855 to 945 Nm ³ , and when the amount of Si in the molten iron is 1.01 to 1.5%, the total amount of oxygen blown into the converter 997.5 to 1102.5Nm ^{3 When} the Si content in the molten iron is 1.51 to 2.0%, the converter refining method characterized in that the total amount of oxygen blown into the converter is 1140 to 1260Nm ³ . The method according to claim 1 or 2, The change time point, When the Si content in the molten iron is 1.0% or less, it is 6% at the time of blowing, and when the Si content in the molten iron is 1.01 to 1.5%, it is 7% at the blowing time, and when the Si content in the molten iron is 1.51 to 2.0% A converter refining method, characterized in that 8% of the time. The method according to claim 1 or 2, Excluding the desulfurized slag, The converter refining method, characterized in that the blowing point to exclude the slag is changed according to the Si content in the molten iron. The method according to claim 1 or 2, The second blowing step, Converter according to claim 1, wherein the slag is excreted in accordance with the content of Si in the molten iron in the molten iron to increase the flow rate in step by step.

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