KR100832527B1 - Method for refining molten steel in converter - Google Patents

Abstract

A method for refining molten steel in a converter is provided to maintain at least 0.08% of the carbon concentration in hot metal, control the phosphorous concentration to not more than 150 ppm, and lower the amount of dissolved oxygen when refining medium carbon steel with at least 0.08% of the carbon concentration in steels that are refined in the converter. A method for refining molten steel in a converter comprises: a preparation step(S100) of coating a converter that has finished a tapping operation of a previous charge, and discharging residual slag; a principal raw material charging step(S200) of charging a principal raw material into the converter; a first refining step(S300) of performing a desiliconizing operation and a dephosphorizing operation of hot metal by using the residual slag of the converter; an intermediate slag discharging step(S400) of discharging refined slag; and a second refining step(S500) of controlling a subsidiary material injection pattern and a blowing pattern in the converter to perform a refining operation such that 0.08 to 0.15% of the carbon concentration and 150 ppm or less of the phosphorous concentration are maintained in hot metal at the finishing time of the second refining operation.

Description

Method for Refining Molten Steel in Converter}

1 is a flowchart of a general converter refining method,

2 is a graph showing the behavior of phosphorus and carbon according to the general blowing progress,

3 is a flowchart showing a converter refining method according to the present invention;

4A is a flowchart showing a first refining step according to the present invention,

4b is a flowchart showing a secondary refining step according to the present invention;

5 is a graph showing the blowing pattern and the subsidiary material input pattern of the embodiment according to the present invention,

Figure 6a is a graph showing the change trend for the phosphorus of the example in a comparative experiment,

Figure 6b is a graph showing the change trend for phosphorus of the comparative example in the comparative experiment.

The present invention relates to a converter refining method, and more specifically, the converter refining process is divided into a primary refining and a secondary refining, and in the first refining step, desulfurization and dephosphorization are carried out using only the residual slag of the converter. It is a method for refining a medium carbon steel converter which performs all operations including decarburization at a stage, thereby saving a separate peat stage and input of carbonate.

1 is a flowchart of a general converter refining method.

As shown in FIG. 1, in general, the refining operation of the converter is to preclude slag, which is a by-product of the refining operation, when the tapping work for transferring the molten steel refined from the converter to the ladle is completed. For reference, slag generated during refining work will be about 150kg per ton of molten steel, of which 50% will be excluded.

When the primary slag is excluded, the converter is established and the remaining slag is injected with light dolomite and fresh dolomite as a coating agent, and high pressure nitrogen is injected to carry out nitrogen spray coating to attach the slag to the furnace wall of the converter.

At this time, the composition of light dolomite and saint dolomite is shown in Table 1 below.

Kinds Mouth dildo Chemical Regulation Melting point Light dolomite 5 ~ 35 CaO≥52 MgO≥37 P≤0.1 S≤0.1 2440 Saint Dolomite 10-35 CaO≥32 MgO≥30 SiO ₂ ≤0.1 Al ₂ O ₃ ≤0.1

When the nitrogen spray coating is completed, the residual slag coating is performed while tilting the converter back and forth using the residual slag remaining on the bottom.

When the remaining slag coating is completed, the secondary slag is excluded. Generally, about 15 to 25 tons of residual slag remain in the converter.

When the second slag exclusion is completed, the ferrous mountain will be carried out using scrap and charter information, and the scrap and charter will be charged to the converter.

When the charging of the molten iron is completed, the blow is started, and the blow is performed to remove impurities in the molten iron by the following reaction while supplying supersonic oxygen through the lance.

[C] + 1/2 O ₂ = CO (g)

[Si] + O ₂ = SiO ₂

[Mn] + 1/2 O ₂ = MnO

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 4 are present in the slag layer while the secondary materials introduced during the converter operation are recycled.

In this case, as shown in FIG. 2, the carbon decreases relatively uniformly as the refining reaction proceeds, and in the case of phosphorus, the phosphorus in the molten iron decreases in the slag according to the increase in basicity, and then decreases after the middle of refining. As the decarburization reaction is at its peak, the return of the slag is returned to the molten iron while oxygen in the slag reacts with the carbon in the molten iron. Will fall.

Manganese also undergoes a refining reaction similar to phosphorus and silicon absorbs into the slag at the beginning of refining.

At 80% of the refining reaction, the temperature of the molten iron and the carbon concentration are measured to determine the state of the molten iron. Using this information, the oxygen consumption at the time of refining is calculated. When oxygen is delivered by the calculated oxygen consumption, converter refining work is completed.

After the converter refining operation is completed, the molten iron temperature and oxygen concentration are measured, and if the target temperature and oxygen concentration are not, re-refining is performed. If the target temperature and oxygen concentration are reached, the tapping work is carried out to transfer the molten steel to the ladle. .

During the tapping work, ferroalloy is added to meet the target components required by the demand price.

In the case of the converter refining operation as described above, the converter end point carbon concentration is usually 0.03 to 0.04%, and the dissolved oxygen is 450 to 1000 ppm. However, in medium carbon steels with a demanded steel grade of 0.08% or more, the carbon content during tapping is low, so that the carbon is re-added during tapping, and because of the high dissolved oxygen, it is added as a deoxidizer. Higher usage leads to an increase in alumina modifier. This has become a problem of lowering the quality of molten steel.

However, when the carbon concentration is at least 0.08% during the refining operation, as shown in FIG. 2, since the phosphorus in the molten iron is at least 200 ppm, the refining operation is terminated when the carbon concentration is at least 0.08%. There was a problem that could not be.

In addition, there was a problem that the operation of the phosphorus unstable operation in the refining method of the general converter.

The present invention has been made to solve the above problems, the present invention in the refining of medium carbon steel of 0.08% or more of the carbon concentration of the steel refined in the converter, while the carbon concentration in the molten iron to less than 150ppm while purifying the carbon concentration of 0.08% or more It is an object of the present invention to provide a converter refining method that can be controlled by the furnace, and the amount of dissolved oxygen can be lowered.

In the converter refining method according to the present invention for achieving the above object, in the converter refining method, the step of preparing a coating for removing the last slag after completing the last charge tapping; A main raw material charging step of charging main raw material into the converter; A first refining step of performing deregulation and dephosphorization of the molten iron using the residual slag of the converter; An intermediate slag discharging step of discharging the refined slag; It characterized in that it comprises a secondary refining step of performing the refining while controlling the sub-material input pattern and the blowing pattern to the converter.

In this case, the basicity (CaO / SiO 2) of the molten iron in the first refining step is preferably maintained at 2.0 to 2.5.

In addition, it is preferable to maintain the silicon (Si) concentration in the molten iron in the first refining step of 0.2 ~ 0.5%.

The primary refining step is divided into a degasser and a dedenser, and the degasser has an L / L0 (cavity depth / melt height) of 0.35 to 0.4, and the demister is L / L0 (cavity depth / melt height). ), While applying a blowing pattern to make 0.09 to 0.12, the low oil flow rate of the degasser and the dephosphorizer is characterized by applying 0.5% of the top flow rate.

In the first refining step, the carbon concentration in the molten iron at the end of the first refining step is preferably 3.8% or more and the phosphorus component is 500 ppm or less.

In the secondary refining step, the sub-material input pattern is inputted at 40% of the total input amount of the sub-materials at the beginning of the second refining step, and 30% of the total input amount of the sub-materials at 40% of the total refining process. In this case, 30% of the total input of subsidiary materials is input at the time of 60% of the total refining process.

In addition, in the secondary refining step, the blowing pattern is initially set to L / L ₀ (cavity depth / melt height) to 0.35 to 0.4, and L / L ₀ (cavity at 40% progress of the total refining process). Depth / melt height) to be 0.55 to 0.59, and at 60% of the total refining process, set L / L ₀ (cavity depth / melt height) to 0.48 to 0.5 and proceed to 80% of the total refining process. At this point, L / L ₀ (cavity depth / melt height) is set to be 0.44 to 0.48.

Thus, in the secondary refining step, the carbon concentration in the molten iron at the end of the secondary refining step is preferably 0.08 to 0.15%, and the phosphorus component is 150 ppm or less.

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

3 is a flowchart showing a converter refining method according to the present invention, Figure 4a is a flowchart showing a first refining step according to the present invention, Figure 4b is a flowchart showing a second refining step according to the present invention.

As illustrated in FIG. 3, the converter refining method according to the present invention includes a preparatory step of coating a converter that has largely finished charge tapping and excluding residual slag; A main raw material charging step of charging main raw material into the converter; A first refining step of performing deregulation and dephosphorization of the molten iron using the residual slag of the converter; An intermediate slag discharging step of discharging the refined slag; And a second refining step of performing refining while controlling the sub-material input pattern and the blowing pattern in the converter.

1. Preparation step (S100)

All charges are completed. At this time, the amount of slag generated during converter refining generally generates 150 kg of slag per ton of molten steel.

And, when the tapping work is completed, the worker excuses the slag remaining in the converter.

After the first slag is discharged, the converter is established, the light dolomite and the fresh dolomite are added to cool the slag while increasing the amount of MgO in the slag, and the supersonic nitrogen is injected onto the slag to protect the refractory of the converter. Conduct.

After nitrogen spray coating is completed, residual slag coating is performed to coat the furnace body by tilting the converter back and forth.

When the remaining slag coating is completed, the slag is secondarily excluded, and the following Table 2 shows the composition of the endpoint slag.

Al ₂ O ₃ CaO MgO Mno P ₂ O ₅ SiO ₂ T.Fe 3.0 45.0 8.5 2.5 2.8 10.00 18.0

The preparation step proceeds in the same manner as the conventional conventional converter refining method.

In the secondary exhaust of slag, in order to maintain basicity at 2.0 to 2.5 in the following first refining step, the amount of residual slag is preferably about 20 to 25 tons based on a 300 ton class converter.

2. The main raw material charging step (S200)

When the refining preparation is completed, fermentation is carried out using scrap and charter information, and the scrap and charter are charged into the converter.

3. First refining step (S300)

Desulfurization and dephosphorization at the same time using only the residual slag of the converter at the same time, it is preferable to control the silicon concentration in the molten iron to 0.2 ~ 0.5% for efficient reaction of the desilification and dephosphorization.

Prior to the start of the blowing, subsidiary materials such as sintered ore, slag preparation, etc. may be added. In order to control the silicon concentration under the above conditions, ferrosilicon (Fe-Si) may be added. The dose of ferrosilicon can be obtained by

Fe-Si (ferosilicon) input amount

= ((Target concentration-concentration of silicon in the molten iron) × (melt dose)

     / (Si content rate in Fe-Si X yield)) * 100

= ((0.30%-concentration of silicon in molten iron) x molten iron (Kg) / (75% x 100%)) x 100

It is desirable to control the silicon concentration in the molten iron by adding the ferro silicon (Fe-Si) calculated by the reaction scheme 5.

3-1. Deregulation Stage

It is a step to lower the concentration of silicon in the molten iron.

Since silicon reacts before carbon at a low temperature, it is preferable to induce the reaction to occur early in the refining process, and precisely, it is desirable to maintain the de-silicon to 10% of the refining process.

At this time, it is desirable to maintain L / L ₀ (cavity depth / melt height) at 0.35 to 0.4 so that the oxygen flows quickly while maintaining the height of the lance while increasing the oxygen flow rate. It is preferable to keep it at 5% or more.

3-2. Deining stage

It is a step to lower the concentration of phosphorus in molten iron.

In this case, it is desirable to maintain the L / L ₀ (cavity depth / melt height) at 0.09 to 0.12 by maintaining the height of the lance to reduce the direct reaction of oxygen transferred from the lance with the molten steel, and to keep the oxygen flow relatively low. Do.

In the dephosphorization step, it is preferable to finish the refining at the time of 15-25% of refining. At this time, an active reaction occurs between the slag and the molten iron and the swelling of the slag is maximized.

The maximum swelling of the slag means that the slag swelling is maximized, because the swelling of the slag is generated by iron oxide contained in the slag, so that the phosphorus of the molten iron can be absorbed to the maximum in the slag.

As described above, in order to maintain a carbon concentration of at least 0.08% and a phosphorus content of 150 ppm or less at the completion of refining and dephosphorization steps, the carbon concentration in the molten iron is maintained at 3.8% or more and the phosphorus content is 500 ppm or less. It is preferable to

4. Slag middle discharging step (S400)

This step is to exclude the refined slag. That is, after finishing the desulfurization and dephosphorization refining, the intermediate discharging step for removing the high concentration of oxide (P ₂ O ₅ ) trapped in the slag.

To this end, the converter is continuously tilted to reach the shortest time at the melt-free spraying angle, for example, 87 degrees, and further tilted at a low speed after reaching the melt-free spraying safety angle to maximize the slag discharge. At this time, the amount of slag to be excluded is preferably to exclude 2.5 to 5% of the total amount of charge.

5. 2nd refining stage (S500)

In the second refining step, the blowing pattern and the subsidiary input pattern are controlled.

At this time, the added raw materials are inputted with raw materials containing ladle slag and iron oxide, for example, semi-mineral, sintered ore, mill scale, etc., to recycle quicklime and reconstruct slag.

The target temperature of the molten iron at the time of the maximum activation of the secondary refining is 1580 degrees and the target of the carbon concentration is 0.5%.

At the end of the secondary refining, the carbon concentration in the molten iron is 0.08 to 0.15% and the phosphorus component is 150 ppm or less.

5-1. Post 2nd refining stage

At the beginning of the second refining, the L / L ₀ (cavity depth / melt height) is maintained at 0.35 to 0.4 to keep the lance height high while increasing the flow of oxygen to prevent slinging and promote slag goods.

In addition, quicklime and light borosilicate are added in a batch, and sintered ore is interlocked. In this case, 40% of the total amount of subsidiary materials calculated is added.

In addition, the flow rate of low odor is adjusted to 0.8% or less of upper odor.

5-2. 2nd refining stage

At 40% of the refining operation, the L / L ₀ (cavity depth / melt height) is maintained at 0.55 to 0.59 by lowering the lance height while increasing the flow rate of oxygen in order to accelerate the decarburization. Therefore, the area that reacts with the molten iron is maximized to promote decarburization.

Meanwhile, quicklime and light small dolomite are added in a batch, and sintered ore is interlocked. In this case, 30% of the total amount of subsidiary materials calculated is added.

5-3. 2nd refining stage

At 60% of the refining operation, the L / L ₀ (cavity depth / melt height) should be kept between 0.48 and 0.50 to slow the carbon response while lowering the lance height and lowering the flow of oxygen.

At this time, quicklime and light dolomite are added in a batch, and sintered ore is interlocked. At this time, 30% of the total amount of subsidiary materials calculated is added.

Therefore, while sintered ore is interlocked, the phosphorus in the slag is prevented from being returned to the molten iron while maintaining the iron oxide (FeO) in the slag at a constant level.

5-4. At the end of the second refining stage

At 80% of the refining operations, the L / L ₀ (cavity depth / melt height) is increased from 0.48 to 0.50 by lowering the flow rate of oxygen while increasing the height of the oxygen lance to slow down the reaction of oxygen in the molten iron. Keep it.

In the second refining stage, the minor raw materials, such as quicklime and light bovine dolomite, are added little by little at each time point because the melting point of the quicklime is higher than 2500 degrees. For this reason, the raw material containing iron oxide is added little by little while quick lime is added to increase the basicity of the slag and to prepare the slag which is good for the slag to absorb the phosphorus in the molten iron.

6. Completion step (S600)

When the secondary refining is completed, the temperature of the molten iron and the carbon concentration are measured to determine the situation in the molten iron. Using this information, the oxygen consumption at the time of refining is calculated. When oxygen is delivered by the calculated oxygen consumption, converter refining work is completed.

The process of calculating the oxygen consumption is omitted because it is common to those skilled in the art.

After the converter refining operation is completed, the molten iron temperature and oxygen concentration are measured, and if the target temperature and oxygen concentration are not, re-refining is performed. If the target temperature and oxygen concentration are reached, the tapping work is carried out to transfer the molten steel to the ladle. .

At this time, the ferroalloy can be added according to the demand of the demand price.

Hereinafter, the Example according to the converter refining method of this invention, and the comparative example according to the conventional converter refining method are compared and demonstrated.

When the tapping of the last charge is completed in both the examples and the comparative examples, the nitrogen spray coating and the residual slag coating is completed, and then have different molten iron temperature and composition by varying the conditions of the examples and comparative examples as shown in Table 3 below. A comparative experiment was carried out by charging the molten iron.

division Melting Temperature (℃) C (%) Si (%) Mn (%) P (%) S (%) Comparative Example 1 1375 3.2 0.001 0.102 0.078 0.008 Comparative Example 2 1376 3.5 0.001 0.112 0.073 0.007 Comparative Example 3 1384 4.1 0.002 0.154 0.076 0.006 Comparative Example 4 1379 4.12 0.001 0.089 0.068 0.005 Comparative Example 5 1345 3.89 0.001 0.145 0.069 0.008 Example 1 1381 3.84 0.001 0.089 0.048 0.005 Example 2 1379 3.95 0.001 0.107 0.039 0.005 Example 3 1383 3.81 0.001 0.098 0.046 0.008 Example 4 1377 3.85 0.001 0.103 0.047 0.008 Example 5 1380 3.92 0.001 0.112 0.038 0.007

And, according to the embodiment of the present invention charged with the molten iron of Examples 1 to 5 was performed by dividing control of each pattern as shown in Figure 5 in the blowing pattern and the sub-material input pattern during refining, Comparative Examples 1 to 5 The comparative example according to the conventional method which loaded the molten iron of the following performed the general blowing pattern and the sub raw material input pattern.

Examples 1 to 5 according to the converter refining method of the present invention by charging the molten iron having the molten iron temperature and the composition of the composition shown in Table 3 proceeds to the first refining step, Comparative Examples 1 to 5 according to the conventional converter refining method The slag composition at 20% of refining progress, which is expected to proceed with the denitrification and dephosphorization stage, was investigated and the results are shown in Table 4 below.

At this time, in the charging step of the main raw materials, Examples 1 to 5 did not add quicklime, Comparative Examples 1 to 5 was used to input the quicklime according to the passion acid.

division Al ₂ O ₃ CaO MgO MnO P ₂ O ₅ SiO ₂ T.Fe basicity Comparative Example 1 2.37 42.52 7.99 2.99 2.31 11.62 20.89 3.7 Comparative Example 2 2.4 39.18 7.04 3.98 2.43 11.85 22.5 3.3 Comparative Example 3 2.19 42.88 7.12 3.06 2.43 9.94 22.45 4.3 Comparative Example 4 2.43 39.81 6.72 3.81 2.49 11.51 21.63 3.5 Comparative Example 5 2.44 38.32 6.65 4.43 2.61 12.52 21.99 3.1 Example 1 2.68 34.91 7.81 4.08 2.86 12.56 21.81 2.8 Example 2 2.52 34.6 7.52 3.74 2.86 14.11 24.3 2.5 Example 3 2.84 35.14 7.51 4.29 2.83 13.73 22.71 2.6 Example 4 2.55 36.67 7.52 4.38 2.88 13.66 22.01 2.7 Example 5 2.58 38.06 7.95 4.19 2.83 13.62 22.4 2.8

As can be seen in Table 4, in Comparative Examples 1 to 5 of the prior art in which quicklime was added, P ₂ O ₅ was lowered to 2.6 or lower while the basicity was high as 3.3 or higher, and the concentration of phosphorus (P) in molten iron was high. It can be expected to perform.

In Examples 1 to 5 of the present invention without the addition of quicklime, the basicity was only about 2.7, using only basicity in the residual slag, and P ₂ O _{5 was} also higher than 2.8. We can expect the earnings to go below 500 ppm.

This is because if the amount of P ₂ O _{5 in} the slag is detected, the phosphorus concentration in the molten iron is lowered by that amount.

And the Example performs secondary refining according to this invention, and the comparative example performed the remaining refinement according to the conventional method.

The dissolved oxygen content and composition of molten steel at the point of refining were investigated, and the results are shown in Table 5 below.

division Dissolved oxygen (ppm) C (%) Si (%) Mn (%) P (%) S (%) Comparative Example 1 450 0.05 0 0.078 0.05 0.008 Comparative Example 2 430 0.054 0 0.068 0.018 0.007 Comparative Example 3 400 0.059 0 0.074 0.019 0.006 Comparative Example 4 395 0.059 0 0.068 0.021 0.005 Comparative Example 5 380 0.06 0 0.069 0.023 0.008 Example 1 350 0.08 0 0.098 0.015 0.005 Example 2 301 0.093 0 0.089 0.01 0.005 Example 3 265 0.149 0 0.093 0.0102 0.008 Example 4 324 0.09 0 0.095 0.0135 0.008 Example 5 312 0.091 0 0.093 0.0125 0.007

As can be seen in Table 5, it can be seen that the amount of dissolved oxygen dissolved in the molten steel in the Example is lower than in the comparative example.

In addition, according to the present invention, the concentration of carbon can be blown up to 0.08% or more without adding a separate carbonization agent, and at the same time, the concentration of phosphorus can be adjusted to 0.015% (= 150 ppm) or less.

In addition, changes in phosphorus (P) components of Examples 1 to 5 and Comparative Examples 1 to 5 were examined during the refining process, and the results are shown in FIGS. 6A and 6B.

6A is a graph showing a change trend for phosphorus in an example in a comparative experiment, and FIG. 6B is a graph showing a change trend for phosphorus in a comparative example in a comparative experiment.

As can be seen in Figures 6a and 6b, it can be seen that according to the present invention it is possible to stably control the behavior of phosphorus during the converter refining.

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.

As described above, the present invention uses the residual slag of the converter, after raising the carbon concentration in the molten iron after the purpose, and lowering the oxygen concentration in the molten iron while lowering the concentration of phosphorus, there is no need to add a separate carbonization agent to the molten steel It has the effect of lowering the manufacturing cost.

In addition, the oxygen concentration in the molten steel is low, thereby reducing the amount of aluminum introduced into the deoxidizer, thereby reducing the amount of alumina inclusions generated during deoxidation, thereby obtaining high-quality molten steel.

Claims (8)

In the converter refining method, A preliminary step of coating the converter having completed the last charge tapping and excluding residual slag; A main raw material charging step of charging main raw material into the converter; A first refining step of performing deregulation and dephosphorization of the molten iron using the residual slag of the converter; An intermediate slag discharging step of discharging the refined slag; The secondary refining step of controlling the secondary raw material input pattern and the blowing pattern to the converter at the end of the molten iron in the carbon concentration is 0.08 ~ 0.15%, and the refining step to perform the refining so that the phosphorus component is less than 150ppm Way. The method of claim 1, The converter refining method, characterized in that the basicity (CaO / SiO ₂ ) of the molten iron in the first refining step to maintain 2.0 ~ 2.5. The method of claim 1 or 2 Converter refining method, characterized in that to maintain the silicon (Si) concentration in the molten iron in the first refining step of 0.2 ~ 0.5%. The method of claim 1, The first refining step is divided into degasser and demineralizer, L / L ₀ (cavity depth / melt height) should be 0.35 ~ 0.4 for degasser While applying blow pattern to L / L ₀ (cavity depth / melt height) to 0.09 ~ 0.12, The low odor flow rate of the degasser and the dephosphorizer is applied to the converter refining method, characterized in that applied to 0.5% of the odor flow rate. The method of claim 1, The first refining step is a converter refining method characterized in that the carbon concentration in the molten iron at the end of the first refining step is at least 3.8%, phosphorus component is 500ppm or less. The method of claim 1, wherein the secondary material input pattern in the secondary refining step, At the beginning of the second refining stage, 40% of the total input of subsidiary materials At the time of 40% of the total refining process, 30% of the total input of subsidiary materials is input. A converter refining method characterized in that 30% of the total input of subsidiary materials is injected at the time of 60% of the total refining process. The method of claim 1, wherein the blowing pattern in the secondary refining step, Initially set L / L ₀ (cavity depth / melt height) to 0.35 ~ 0.4, At 40% of the total refining process, L / L ₀ (cavity depth / melt height) should be 0.55 ~ 0.59. At 60% of the total refining process, set L / L ₀ (cavity depth / melt height) to 0.48 ~ 0.5, The converter smelting method characterized in that the L / L ₀ (cavity depth / melt height) to be 0.44 ~ 0.48 at 80% of the total refining process. delete

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