JP2011184752A - Method for desiliconizing molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a refining while sufficiently shortening the time for desiliconizing and dephosphorizing treatments when the desiliconizing treatment and the dephosphorizing treatment are applied by the identical converter type refining furnace. <P>SOLUTION: A space volume of the converter-type refining furnace after charging molten iron, is set to be 0.2-0.6 m<SP>3</SP>/t and further, the basicity of slag is set to be 0.7-1.0 and the oxygen of 2-3 times of the calculated necessary oxygen quantity for needing to the desiliconization, is supplied by the solidus oxygen source and the gaseous oxygen, and the average oxygen supplying speed of the solidus oxygen source at the supplying time, is set to be 0.8-2.5 kg-O/t/min. Further, the desiliconizing treatment, in which the average oxygen supplying speed of the gaseous oxygen is set to be 0.9-1.4 Nm<SP>3</SP>/t/min is performed at one or more times and also, the lowering rate of the silicon in the desiliconizing treatment is 0.4-0.6 mass% and the silicon concentration in the molten iron before the dephosphorizing treatment becomes &le;0.4 mass% through the desiliconizing treatment and after completing the desiliconizing treatment, successively, the dephosphorizing treatment is performed without performing the removal of the desiliconized slag by inclining the converter-type refining furnace. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a hot metal desiliconization method in which hot metal desiliconization and dephosphorization are performed using the same converter-type refining furnace.

Conventionally, hot metal discharged from a blast furnace is generally desiliconized before dephosphorization, and hot metal desiliconization is performed in a converter (converter type refining furnace). As the technique shown, there are those shown in Patent Document 1 and Patent Document 2.
In Patent Document 1, when hot metal desiliconization treatment is performed on hot metal having a Si content of 0.3% or more using a converter having an upper bottom blowing function, the slag composition after desiliconization has a basicity of 0.5. 7 to 1.8, alumina is 2 to 10%, phosphoric acid is 1 to 8%, (T.Fe) concentration of slag after desiliconization is 10 to 15%, and P in the hot metal after desiliconization is 0. 02 to 0.05%.

In Patent Document 2, the first process of introducing hot metal and scrap into the top-bottom blowing converter, the second process of removing Si and removing P, the third process of discharging generated slag, and then de-C blowing In the converter refining method comprising the fourth step to be performed, if the Si value in the hot metal is high, de-Si treatment is performed before the converter charging, or the Si value is adjusted by performing Si removal after the converter charging, The amount of SiO ₂ present in the slag produced in the second step is in the range of 5 to 10 kg / t, and no fluorite is used in the second step.

JP 2002-241829 A Japanese Patent No. 3735211

In Patent Document 1 and Patent Document 2, after desiliconization processing is performed in a converter, the converter is tilted to discharge slag in the converter, and then dephosphorization processing is performed. That is, in Patent Document 1 and Patent Document 2, after the desiliconization process is completed, the slag in the converter is surely discharged and the dephosphorization process is started.
For this reason, it takes time from desiliconization treatment to dephosphorization treatment, and in situations where the treatment time is determined in advance, the phosphorus concentration is sufficiently increased by dephosphorization treatment performed after desiliconization treatment. There were also situations where it was difficult to reduce.

  Therefore, in view of the above problems, the present invention performs refining while sufficiently shortening the time for desiliconization and dephosphorization when performing desiliconization and dephosphorization in the same converter type refining furnace. It is an object of the present invention to provide a hot metal desiliconization method that can be used.

In order to achieve the above object, the present invention has taken the following measures.
That is, the technical means for solving the problems in the present invention is to convert the hot metal desiliconization process and the dephosphorization process using the same converter type refining furnace, and to convert the converter type after charging the hot metal. Calculation required for desiliconization by setting the upper space volume in the smelting furnace to 0.2 to 0.6 m ³ / t and adding CaO flux to make the slag basicity 0.7 to 1.0 2 to 3 times the required amount of oxygen is supplied by a solid oxygen source and gaseous oxygen, the average oxygen supply rate of the solid oxygen source at the time of supply is 0.8 to 2.5 kg-O / t / min, and The desiliconization treatment is performed at least once with the average oxygen supply rate of the gaseous oxygen being 0.9 to 1.4 Nm ³ / t / min, and the silicon decrease amount in the desiliconization treatment is 0.4 to 0.6 mass. And the silicon concentration in the hot metal before the dephosphorization treatment is reduced to 0.4 mass% or less. To so that, after desiliconization treatment terminates without Haikasu of desiliconization slag by tilting the converter type refining furnace, subsequently lies in performing dephosphorization process.

  ADVANTAGE OF THE INVENTION According to this invention, when performing a desiliconization process and a dephosphorization process in the same converter-type refining furnace, refining can be performed, fully shortening the time of a desiliconization and a dephosphorization process.

It is a whole side view of a converter type refining furnace. It is a related figure of the average oxygen supply speed | rate of gaseous oxygen when a desiliconization process is performed once, and process time. It is a related figure of the average oxygen supply rate of gaseous oxygen when a desiliconization process is performed twice, and processing time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a converter type refining furnace used in the hot metal desiliconization method of the present invention. The converter type refining furnace 1 has an upper blowing function, and performs desiliconization treatment (desiliconization blowing) and dephosphorization treatment (dephosphorization blowing) of the hot metal 2 discharged from the blast furnace in the same furnace. Is.
The converter-type refining furnace 1 includes a furnace port 3 that opens upward. In the converter type refining furnace 1, an upper blowing lance 4 for blowing oxygen into the hot metal 2 charged in the converter type refining furnace 1 is provided to be freely inserted from the furnace port 3. Further, a blowing lance (refractory lance) 7 for blowing a gas (for example, nitrogen gas) for stirring the hot metal 2 charged in the converter type refining furnace 1 is introduced into the converter type refining furnace 1. Is provided to be freely inserted from the furnace port 3. The converter-type refining furnace 1 is provided with a chute 5 for introducing auxiliary materials, a refining agent, and the like. On the furnace wall of the converter type refining furnace 1, a hot water outlet 6 is formed so that the hot metal 2 can be poured out by tilting the furnace body.

In order to perform refining using such a converter-type refining furnace 1, for example, molten iron 2 discharged from a blast furnace is charged into the converter-type refining furnace 1, and auxiliary materials, refining agents, etc. are passed through a chute 5. Into molten iron 2. Moreover, gaseous oxygen is supplied through the upper blowing lance 4, solid oxygen is supplied through the chute 5, or nitrogen is blown from the refractory lance 7 to perform the treatment while stirring the molten iron 2.
Note that the converter type refining furnace shown in FIG. 1 is an example for performing a desiliconization process and a dephosphorization process, and these processes are not limited to the converter type refining furnace shown in FIG. For example, instead of blowing nitrogen from the refractory lance 7 and stirring the molten iron 2, treatment is performed while blowing the gas such as argon, nitrogen and carbon monoxide from the tuyeres at the bottom of the furnace and stirring the molten iron 2. A simple converter-type smelting furnace may be used.

Now, in the hot metal desiliconization method of the present invention, the same converter type refining furnace 1 is used to perform the desiliconization process and the dephosphorization process. That is, after the desiliconization process, the hot metal 2 is removed from the converter type refining furnace 1. The target is to continue dephosphorization without hesitation.
Hereinafter, the hot metal desiliconization method will be described in detail.
About space volume
In refining, the converter-type refining furnace 1 is charged with the hot metal 2, and the space volume above the converter-type refining furnace 1 after the hot metal 2 is charged is 0.2 to 0.6 m ^3. / T or less. That is, in the converter-type smelting furnace 1 immediately after the hot metal 2 is charged (before the start of blowing), the internal volume of the converter-type smelting furnace (the volume in a state where the main raw material such as the hot metal 2 is not charged). ), The volume on hot metal 2 excluding the volume occupied by the main raw material such as hot metal 2 is 0.2 to 0.6 m ³ / t in terms of 1 ton of main raw material after charging. Main raw materials such as 2 are charged into the converter type refining furnace 1. For example, when 90 t of hot metal is charged, the upper space volume in the converter refining furnace 1 is 18 to 54 m ³ .

The space volume is, for example, volume (m ³ ) = inner furnace volume− (charged molten iron amount t) ÷ (specific gravity of molten iron t / m ³ ) − (charged cold iron source amount t) ÷ (cold iron source specific gravity) t / m ³ ) can be obtained by dividing the main raw material charge including hot metal, that is, the main raw material charge (= hot metal + cold iron source) (t). As for the volume in the furnace, it is preferable to consider the influence of the metal in the furnace and the wear of bricks using a laser profile meter or the like.

In addition, as will be described later, in the desiliconization processing method of the present invention, conditions for the desiliconization treatment are set in a situation where the space volume of the converter-type refining furnace 1 is 0.2 or more and 0.6 m ³ / t or less. As a result, slag forming is forcibly generated during the desiliconization process, and an appropriate amount of the formed slag is discharged from the furnace port 3 to the outside of the converter-type refining furnace 1 (sometimes simply outside the furnace). I am going to do that.
"About silicon concentration and basicity"
The hot metal 2 charged into the converter type refining furnace 1 is not subjected to desiliconization in advance, and the hot metal discharged from the blast furnace is charged into the converter type refining furnace 1 as it is. is there. The silicon concentration (silicon concentration) of the hot metal discharged from the blast furnace usually varies from 0.15 to 0.80 mass%, and in particular, in recent blast furnaces, an operation method using an inexpensive fuel is directed. Therefore, the silicon concentration may increase. In some cases, the silicon concentration of the hot metal 2 may be 1.0 mass% or more.

When the silicon concentration of the hot metal 2 is high, for example, when the silicon concentration of the hot metal 2 is 0.7% by mass or more, it is considered that SiO ₂ generated during the desiliconization reaction is 15 kg / t or more. If it is attempted to complete the desiliconization and dephosphorization of the hot metal 2 by one blowing, for example, as described in Japanese Patent No. 3735211, a basicity of about 2 must be secured. The required amount of CaO is 30 kg / t, and the amount of slag is approximately 70 kg / t.

In addition, the amount of slag after performing a desiliconization process or a dephosphorization process can be calculated | required by the amount of slag = [required CaO amount (kg / t) / CaO density | concentration (mass%) in slag], for example. The concentration of CaO and the concentration of SiO ₂ in the slag when desiliconization or dephosphorization is performed with the basicity of the slag being about 2, as a result of sampling and analysis in actual operation, for example, CaO: 44% by mass and SiO ₂ : 22% by mass.

Further, when it is considered that the silicon concentration of the molten iron 2 is 1.0 mass%, SiO ₂ produced during the desiliconization reaction is 21 kg / t or more. As described above, when desiliconization and dephosphorization are completed by one blowing of such hot metal 2, the required CaO amount is 42 kg / t, and the slag amount is approximately 95 kg / t. .
In order to process the hot metal 2 having a high hot metal silicon concentration, as described above, a large amount of CaO is required and a lot of slag is generated. If blowing is performed with a large amount of slag, a large amount of slag tends to come out of the converter type refining furnace 1 due to slag forming, and if a large amount of slag goes out of the furnace, desiliconization occurs. There is also a possibility that slag for processing or dephosphorization processing cannot be secured. Therefore, in the present invention, when the hot metal 2 having a high hot metal silicon concentration is processed, the slag is discharged by forming the slag by setting conditions for the desiliconization treatment. The silicon treatment and dephosphorization treatment are to be carried out smoothly.

Specifically, in performing the desiliconization treatment performed before the dephosphorization treatment, the basicity (CaO / SiO ₂ ) of slag (desiliconization slag) is set to 0.7 to 1.0 by adding a CaO-based flux. Yes. As disclosed in Japanese Patent Application Laid-Open No. 10-152714, generally, when the desiliconization process is performed, if the basicity of the slag is in the range of 0.3 to 1.3, the hot metal temperature is 1300 ° C., for example. Even so, the slag has good fluidity and is suitable for desiliconization treatment. Here, when the basicity of slag is 1.3, it can be said that slag forming is likely to occur.

  However, when the basicity of the slag is larger than 1.0, a relatively large amount of CaO is required, and the amount of slag generated during the desiliconization process increases. There is a risk that the amount of slag discharged to the outside will be excessive. If the amount of slag discharged to the outside of the furnace is large, the slag accumulates in the bottom of the furnace, for example, a carriage that moves under the furnace (for example, a carriage equipped with a ladle ladle) cannot be run, It takes a lot of time to remove the slag deposited below. Therefore, the upper limit value of the slag basicity in the desiliconization process needs to be 1.0 or less.

On the other hand, when the basicity of the slag is less than 0.7, the amount of slag generated during the desiliconization process is small, and the amount of slag discharged from the furnace port 3 to the outside of the furnace due to slag forming may be reduced. There is. In such a case, since slag discharged out of the furnace is small, so that the number of SiO ₂ after desiliconization treatment put away residual. Then, when the process shifts to the dephosphorization process after the desiliconization process, even if CaO is added, the slag remaining in the furnace does not easily become a slag (dephosphorization slag) for the dephosphorization process. That is, when the basicity of the slag is less than 0.7, a large amount of SiO ₂ is present in the slag after the desiliconization treatment, and it is difficult to generate slag for performing the dephosphorization treatment. Therefore, the basicity of the slag when performing the silicon removal treatment is 0.7.
It must be in the range of -1.0.

The input amount of the CaO-based slacks added to achieve the target basicity is, for example, the input amount of the CaO-based slacks = [desiliconization amount (mass%) ÷ silicon atomic weight (28) × silica molecular weight (60). × 10 (kg / t / mass%)] × target basicity ÷ CaO pure content (%) in CaO flux.
“Supply of solid oxygen source and gaseous oxygen”
Further, in the present invention, by forming slag at the time of desiliconization treatment, an appropriate amount of slag is discharged out of the furnace. It is supplied by an oxygen source and gaseous oxygen.

If excess oxygen is supplied during desiliconization, the carbon (C) decarburization reaction proceeds in the hot metal, and fine CO bubbles are generated in the slag (desiliconized slag), forming the slag. To do.
When the amount of oxygen supplied (the amount of oxygen supplied) is less than twice the amount of oxygen required for calculation, the amount of slag forming is insufficient, the amount of slag discharged from the furnace port 3 is small, and the slag before dephosphorization treatment Is not enough. On the other hand, when the amount of supplied oxygen exceeds three times the amount of oxygen required for calculation, the decarburization reaction rate becomes too high and the amount of slag forming increases. Therefore, the amount of slag discharged from the furnace port 3 increases, and as described above, it takes a long time to remove the slag accumulated under the furnace or the carriage moving under the furnace cannot travel. End up. In addition, when the dephosphorization process is continued after the desiliconization process, the amount of slag required for the dephosphorization process is small, so that a large amount of CaO-based flux must be input during the dephosphorization process. During the phosphorous treatment, the CaO flux cannot be dissolved in a short time, which may hinder the dephosphorization treatment. Therefore, the supply oxygen amount needs to be 2 to 3 times the calculated oxygen amount.

The required oxygen amount is the required oxygen amount when it is assumed that the desiliconization reaction proceeds by a reaction of Si + O ₂ → SiO ₂ (when the desiliconization oxygen efficiency is assumed to be 100%). Amount = [desiliconization amount (mass%) × 10 (kg / t / mass%) ÷ silicon atomic weight (28)] × 22.4 Nm ³ / kmol.
"Average oxygen supply rate of solid oxygen source"
As described above, oxygen that is 2 to 3 times the amount of oxygen necessary for calculation is supplied by the solid oxygen source and gaseous oxygen. When the solid oxygen source is supplied, the average oxygen supply rate is set to 0. 8 to 2.5 kg-O / t / min. “Kg-O” means the mass of oxygen contained in the solid oxygen source, and the average supply rate is defined based on the amount.

When the solid oxygen source is supplied, the solid oxygen source and the molten iron come into contact with each other to be heated or dissolved to form a molten iron oxide layer in the slag. Iron oxide (FetO) in the molten iron oxide layer is consumed in the oxidation reaction of silicon, carbon, etc. in the hot metal near the hot metal interface.
Now, when performing desiliconization treatment, the supply of the CaO-based flux containing CaO from the top of the converter type refining furnace 1, so that the slag CaO-SiO ₂ system is formed, the initial desiliconization treatment At the stage, the amount of SiO ₂ produced is small and the dissolution of CaO is not sufficiently promoted. Therefore, in order to promote dissolution of CaO by setting the FeO concentration in the slag to 20% or more, it is necessary to set the average oxygen supply rate of the solid oxygen source to 0.8 kg-O / t / min.

  On the other hand, heat of dissolution is required to melt the solid oxygen source, and the heat of dissolution increases as the average oxygen supply rate of the solid oxygen source increases. Here, if the average oxygen supply rate of the solid oxygen source is larger than 2.5 kg-O / t / min, the dissolution of the solid oxygen source is hindered because the heat of dissolution is too large, and the vicinity of the hot metal and slag interface The ratio of the solid oxygen source that contributes to the oxidation reaction of silicon, carbon, etc. becomes small. In particular, if the average oxygen supply rate of the solid oxygen source is made larger than 2.5 kg-O / t / min, the formation of the molten iron oxide layer in the slag deteriorates, and the decarburization reaction for forming the slag Decreases and the amount of slag discharged from the furnace port 3 decreases.

For this reason, the average oxygen supply rate of the solid oxygen source needs to be 0.8 to 2.5 kg-O / t / min.
When the desiliconization processing time is T (min), the average oxygen supply rate of the solid oxygen source is “average oxygen supply rate of solid oxygen source = solid oxygen source mass supplied during T time (kg / t)” × (mass% of oxygen combined with iron in the solid oxygen source) ÷ T ”. Moreover, the supply method (input method) of the solid oxygen source may be added all at once when performing the desiliconization treatment, may be added continuously, or may be divided every predetermined time.
“Average oxygen supply rate of gaseous oxygen”
When supplying gaseous oxygen, the average oxygen supply rate is set to 0.9 to 1.4 Nm ³ / t / min. When gaseous oxygen is supplied using the top blow lance 4, the hot metal surface is recessed due to collision of gaseous oxygen. Generally, when the supply rate of gaseous oxygen (average oxygen supply rate) is reduced, the recess becomes shallower and larger. Then the dent becomes deeper. Here, if the average supply amount of gaseous oxygen is reduced, the collision pressure of gaseous oxygen on the hot metal decreases, so the amount of oxygen that penetrates into the hot metal decreases, and oxygen contributing to the oxidation of silicon and carbon in the hot metal decreases. Will do. Considering this, in order to cause a decarburization reaction that generates enough slag to discharge slag from the furnace port 3 in addition to the desiliconization reaction, the average oxygen supply rate of gaseous oxygen is set to 0. It is necessary to set it to 9 Nm ³ / t / min or more.

On the other hand, when the average oxygen supply rate of gaseous oxygen is increased, the collision pressure of gaseous oxygen on the hot metal increases, so the amount of oxygen that penetrates into the hot metal increases, and oxygen that contributes to the oxidation of silicon and carbon in the hot metal is increased. Will increase. Therefore, oxygen contributing to the decarburization reaction increases, and sufficient slag forming can be caused to be discharged from the furnace port 3 by the generated carbon monoxide (CO) gas. However, if the average oxygen supply rate of gaseous oxygen exceeds 1.4 Nm ³ / t / min, the decarburization reaction rate becomes too high, and the amount of slag discharged from the furnace port 3 increases. As a result, as described above, for example, the carriage moving under the furnace becomes incapable of traveling, it takes a long time to remove the slag accumulated under the furnace, or CaO can be quickly removed during the dephosphorization process. The flux cannot be dissolved, and there is a risk of hindering the dephosphorization process.

In particular, when the space volume in the converter-type refining furnace 1 after the molten iron is charged is set to 0.2 to 0.6 m ³ / t, the average oxygen supply rate of gaseous oxygen is 2.0 Nm ^3. When exceeding / t / min, the decarburization reaction rate for slag forming has increased remarkably, and slag containing a large amount of granular iron overflows from the furnace port 3 and causes serious environmental problems such as fuming. There is.

If the desiliconization processing time is T (min), the average oxygen supply rate of gaseous oxygen can be determined by the amount of gaseous oxygen supplied during the time period T (Nm ³ / t) ÷ T. Moreover, the supply rate of gaseous oxygen may be constant or variable, and may be any as long as it satisfies the average oxygen supply rate during the blowing period.
"About the amount of silicon decrease per time"
In the present invention, the amount of silicon decrease per desiliconization treatment as described above is 0.4 to 0.6 mass%. That is, the basicity of the slag is set to 0.7 to 1.0, and oxygen that is 2 to 3 times the required oxygen amount is supplied by the solid oxygen source and the gaseous oxygen. In the desiliconization treatment in which the average oxygen supply rate of gaseous oxygen is set to 8 to 2.5 kg-O / t / min and 0.9 to 1.4 Nm ³ / t / min, the amount is reduced per time [Si]. Of 0.4 to 0.6 mass%.

When the amount of silicon removal (ΔSi: difference in silicon concentration before and after the silicon removal treatment) to be reduced in the silicon removal treatment is less than 0.4 mass%, for example, the amount of SiO ₂ produced in the furnace by the silicon removal reaction Is 8.6 kg / t or less. In this state, the amount of CaO required for one desiliconization process varies depending on the target basicity, but is smaller than 6 to 8.6 kg / t, and the amount of slag in the furnace may be smaller than 19 to 23 kg / t. . As a result, even if forming is forcibly performed during the desiliconization process, the amount of SiO ₂ discharged from the furnace port 3 is insufficient and a large amount of SiO ₂ remains in the converter-type refining furnace 1. Under these circumstances, it is difficult to generate dephosphorization slag during dephosphorization, and unexpected slag forming occurs during dephosphorization, resulting in a shortage of dephosphorization slag. May not drop to the desired value.

When the desiliconization amount to be reduced in the desiliconization process is larger than 0.6% by mass, for example, the amount of SiO ₂ produced in the furnace by the desiliconization reaction is 13 kg / t or more. Although the amount of CaO necessary for the silicidation varies depending on the target basicity, it becomes larger than 9 to 13 kg / t, and the amount of slag in the furnace becomes larger than 28 to 35 kg / t. As a result, when forming is forcibly performed during the desiliconization process, the amount of desiliconization slag overflowing from the furnace port 3 becomes excessive, and the process must be temporarily suspended, so that productivity may be reduced.

The amount of slag after desiliconization is, for example, required CaO amount = [desiliconization amount (mass%) × 10 (kg / t / mass%) × 60/28] × target basicity, slag amount = [necessary. CaO amount (kg / t) ÷ CaO concentration in slag (mass%)].
The concentration of CaO in the slag and the concentration of SiO ₂ when the desiliconization treatment is carried out at a basicity of about 0.7 are the result of sampling and analysis in actual operation. For example, CaO: 32% by mass, SiO ₂ : 46% by mass. Further, when the desiliconization treatment is performed at a basicity of about 1.0, CaO: 37 mass% and SiO ₂ : 37 mass%.

In addition, in the present invention, the silicon concentration of the hot metal before the dephosphorization process is transferred, that is, before the dephosphorization process is set to 0.4 mass% or less. Here, when the state in the dephosphorization process is considered, for example, as disclosed in Japanese Patent No. 3735211, a large amount of slag can be processed without overflow from the furnace port 3 during the dephosphorization process. The total amount of slag is preferably 60 kg / t or less. If the amount of SiO _{2 in} the slag during the dephosphorization process is 5 to 10 kg / t, the total slag amount can be reduced to 60 kg / t or less, and the dephosphorization reaction is not hindered.

Therefore, in consideration of the amount of SiO ₂ remaining in the furnace after the desiliconization treatment, the silicon concentration in the hot metal before the dephosphorization treatment is obtained. The silicon concentration (desiliconization concentration) in the hot metal before the dephosphorization treatment is 0.4. It is necessary to make the mass% or less.
"Number of desiliconization processes"
In the present invention, when the silicon concentration does not become 0.4 mass% or less after one desiliconization treatment, the silicon removal treatment is repeatedly performed until the silicon concentration becomes 0.4 mass% or less. . In other words, in the present invention, the desiliconization process is performed once or more.

  If the desiliconization process is performed under the above-described conditions, it is possible to discharge an appropriate amount of slag out of the furnace before the dephosphorization process by one desiliconization process. Since the silicon concentration to be decreased to 0.6% by mass or less, when the silicon concentration of the molten iron is very high, the silicon concentration may not become 0.4% by mass or less after one desiliconization process is completed. . In such a case, considering the amount of slag generated by the desiliconization process again, the desiliconization process is performed once or more so that the residual desiliconization slag amount in the furnace before the dephosphorization process is within a predetermined range. Repeat. When the desiliconization process is repeatedly performed, as shown in FIG. 3, once the supply of gaseous oxygen is stopped and the preparation process for the next desiliconization process is performed, then the supply of gaseous oxygen is started again. To do. That is, in the present invention, desiliconization blowing from the start of supply of gaseous oxygen to the stop is counted as one time.

And in this invention, if the silicon concentration of the hot metal after desiliconization processing (before dephosphorization processing) will be 0.4 mass% or less, desiliconization slag will not be discharged by tilting of the converter type refining furnace 1. Subsequently, the dephosphorization treatment is carried out in the same manner as those skilled in the art.
“Discharge of slag from the furnace entrance”
In the conventional desiliconization processing method, since the process of discharging the slag from the furnace port 3 is not performed, the forming slag is forcibly settled by using the forming inhibitor or it takes time. After the slag forming naturally subsided, the furnace body was tilted and the slag was discharged from the furnace port 3. In such an operation, for example, when a carbonaceous foaming inhibitor is used, the iron oxide concentration in the slag decreases, and the hatching of CaO newly added in the subsequent dephosphorization process occurs. Oh, dephosphorization reaction was sometimes inhibited. Further, when the slag forming is allowed to settle down over time, it takes a long time to enter the dephosphorization process, and the productivity is significantly deteriorated.

On the other hand, in the present invention, an appropriate amount of slag is discharged to the outside of the furnace through the furnace port 3 during the desiliconization process according to the above-described conditions. There is no need to discharge the slag, and immediately after the preparatory work for the dephosphorization process, the blowing for the dephosphorization process can be started. In addition, in the desiliconization method of the present invention, it is not necessary to add a forming inhibitor and discharge slag outside the furnace. Therefore, immediately after the desiliconization treatment, CaO (flux) is used to increase the basicity by dephosphorization treatment. ) Or a solid oxygen source can be added to lower the slag or hot metal temperature.

In this way, if CaO or a solid oxygen source is added for dephosphorization, the slag is cooled, and the fine CO bubbles in the slag contract, so that the slag is formed in the furnace immediately after the desiliconization process is completed. Even if this occurs, slag calming (slag forming calming) can be achieved.
Table 1 shows the implementation conditions from desiliconization processing to continuous casting using a converter type refining furnace. Tables 2 and 3 summarize the examples in which the hot metal desiliconization method of the present invention was performed based on the conditions of Table 1 and the comparative examples in which the desiliconization was performed by a method different from the present invention. is there.

The implementation conditions will be described in detail.
As shown in Table 1, the converter type refining furnace is a 90 ton class converter. The internal volume of the converter-type refining furnace when the refractory (brick) is applied is 54 m ³ . A gas for stirring the hot metal 2 was blown from a refractory lance 7 capable of blowing powder. Moreover, in the converter type refining furnace 1, only hot metal was used as a main raw material without using a cold iron source such as scrap.

In the hot metal 2 charged into the converter type refining furnace 1, [C] = 4.5 to 4.8% by mass, [P] = 0.10 to 0.120% by mass, [Si] = 0.70 The content was 1.2% by mass. The molten steel type was a general steel whose upper limit value of phosphorus concentration [P] after dephosphorization treatment was 0.020% by mass.
Auxiliary materials such as CaO were determined by controlling ordinary auxiliary materials by those skilled in the art. The solid oxygen source used was a mill scale in which the mass of oxygen combined with iron in the solid oxygen source was 22% by mass. The dephosphorization treatment after the desiliconization treatment was carried out in the same manner as those skilled in the art for melt production.

  In addition, with regard to converter blowing (decarburization treatment), molten steel treatment (secondary refining treatment) after decarburization treatment (after converter steelmaking), and continuous casting performed after dephosphorization treatment, those skilled in the art will be able to follow went.

The evaluation in the examples and comparative examples of each table will be described.
The slag outflow rate during the desiliconization treatment was defined as Wslag (d-si), which was obtained from the CaO concentration in the slag after the desiliconization treatment and the CaO input amount, and dropped into the furnace during the desiliconization treatment. When the measured mass of slag is Wslag (falling), the desiliconization slag outflow rate is a value defined by Wslag (falling) / Wslag (d-si).

As described above, when the amount of slag flowing out of the furnace port 3 is small due to slag forming during the desiliconization process, the SiO ₂ content resulting from the desiliconization slag remaining in the furnace increases, and the slag base of the dephosphorization process Dephosphorization treatment may be hindered because the degree decreases. In addition, when the basic unit of CaO is increased in order to ensure basicity during the dephosphorization process, slopping from the furnace port 3 occurs due to slag forming during the process, and as a result, the amount of slag for dephosphorization is reduced. It may decrease and cause inconvenience in the dephosphorylation reaction. On the other hand, when there is a large amount of slag flowing out of the furnace port 3 due to slag forming during desiliconization, it takes time to remove the desiliconized slag that has fallen and deposited under the furnace, or the desiliconized slag in the furnace is solidified. However, the formation of dephosphorization slag during the dephosphorization process may be delayed, and the phosphorus concentration after the process may not decrease to a desired value.

For this reason, it is necessary that the amount of slag discharged (outflow) from the furnace port 3 during the desiliconization process is not too small and not too large. When expressed in terms of the desiliconization slag outflow rate, the value is 40 to 65. % Range is acceptable. If the desiliconization slag outflow rate is within this range, refining can be performed without interrupting the desiliconization process or the dephosphorization process, and the phosphorus concentration after the dephosphorization process can be within the upper limit of the standard.
In Example 1 to Example 24 of Table 2, the space volume of the converter-type refining furnace after charging the hot metal was 0.2 to 0.6 m ³ / t (space volume on the hot metal), and slag The basicity is 0.7 to 1.0 (column of desiliconization slag basicity), and oxygen 2 to 3 times the amount of oxygen required for desiliconization is supplied by a solid oxygen source and gaseous oxygen. (Desiliconized blown oxygen supply amount / calculated desiliconized oxygen amount column). Further, the average oxygen supply rate of the solid oxygen source is 0.8 to 2.5 kg-O / t / min (column of the average oxygen supply rate of the solid oxygen source), and the average oxygen supply rate of the gaseous oxygen is 0.9 to 1.4Nm ³ / t / min (column of average oxygen supply rate of gaseous oxygen), desiliconization treatment is performed once or more (number of desiliconization treatment), and the amount of silicon decrease in the desiliconization treatment is 0.4 to 0.6% by mass (column of desiliconization amount ΔSi per time). In addition, the silicon concentration of the hot metal before dephosphorization treatment is 0.4% by mass or less by passing through desiliconization treatment (column of hot metal silicon concentration after desiliconization blowing). The dephosphorization slag was not removed by tilting the converter-type refining furnace (the column of the desiliconization slag removal process by tilting the furnace body), and the dephosphorization process was continued.

As shown in FIG. 2, for example, in Examples 5 to 9, the average oxygen supply rate of gaseous oxygen is set to 1.1 Nm ³ / t / min during the desiliconization process. Thus, [Si] of the hot metal was reduced to 0.4 mass% or less, and therefore, dephosphorization was performed without removing the desiliconized slag by tilting the converter type refining furnace.
As shown in FIG. 3, for example, in Examples 21 to 22, the desiliconization process was performed once with the average oxygen supply rate of gaseous oxygen being 1.1 Nm ³ / t / min during the desiliconization process. Thereafter, the second desiliconization treatment was further performed at an average oxygen supply rate of gaseous oxygen of 1.1 Nm ³ / t / min, and the molten silicon [Si] was 0.4% by mass in the second desiliconization treatment. Since it was made as follows, dephosphorization treatment was performed without removing the desiliconization slag by tilting the converter type refining furnace.

  In Comparative Examples 1 and 2, since the basicity of slag in the desiliconization process is less than 0.7, the amount of slag is small, slag forming is insufficient, and sufficient slag can be discharged from the furnace port 3. There wasn't. In Comparative Examples 3 to 4, since the basicity of slag in the desiliconization process is larger than 1.0, the amount of slag is large and the slag forming is too large, and excessive slag comes out from the furnace port 3. I have.

  In Comparative Example 5, since the amount of decrease in silicon per one time was less than 0.4% by mass, the amount of slag was small, slag forming was insufficient, and sufficient slag could not be discharged from the furnace port 3. . In Comparative Example 6, since the amount of decrease in silicon per one time is larger than 0.6% by mass, the amount of slag is large and the slag forming is too large, and excessive slag is generated from the furnace port 3. It was.

In Comparative Examples 7 to 8, since the average oxygen supply rate of gaseous oxygen is higher than 1.4 Nm ³ / t / min, the decarburization reaction rate becomes too high, and large slag forming occurs. Excessive slag came out from 3. In Comparative Example 9, since the average oxygen supply rate of gaseous oxygen is smaller than 0.9 Nm ³ / t / min, the amount of oxygen entering the hot metal is reduced and oxygen contributing to the oxidation of silicon and carbon in the hot metal is reduced. As a result, the forming for discharging the slag from the furnace port 3 could not be generated.

  In Comparative Example 10 and Comparative Example 12, since the average oxygen supply rate of the solid oxygen source was smaller than 0.8 kg-O / t / min, slag forming could not be sufficiently generated. In Comparative Example 11, since the average oxygen supply rate of the solid oxygen source is larger than 2.5 kg-O / t / min, the heat of dissolution for dissolving the solid oxygen source is too large and the dissolution does not proceed. Oxygen that contributes to the oxidation of silicon and carbon was reduced, and forming for discharging slag from the furnace port 3 could not be generated.

  In Comparative Example 13, since the amount of oxygen supplied to the hot metal was less than twice the amount of oxygen required for calculation, slag was not sufficiently formed, and the amount of slag discharged from the furnace port 3 was small. In Comparative Example 14, the amount of oxygen supplied to the hot metal was larger than three times the amount of oxygen required for calculation, so excessive slag forming occurred and the amount of slag discharged from the furnace port 3 was large.

  In Comparative Example 15, the dephosphorization process could not be sufficiently performed because the desiliconization process was not performed once in the same furnace. In Comparative Examples 16 to 17, since slag was discharged by tilting the furnace body after the desiliconization process, it took time to start the dephosphorization process, and a sufficient processing time for the dephosphorization process was secured. I couldn't. That is, in Comparative Examples 16 to 17, when the processing time between the desiliconization process and the dephosphorization process is within a certain time, the start of the dephosphorization process is delayed, and the dephosphorization process is sufficiently performed over time. Could not do. In addition, the numerical value of the amount of slag dropped in the furnace in Comparative Examples 16 to 18 is the amount of slag discharged into the slag pan.

In Comparative Example 18, the space volume of the converter-type smelting furnace after the hot metal was charged exceeded 0.6 m ³ / t, so that the slag was sufficiently discharged from the furnace port 3 under the conditions in the desiliconization process described above. Could not be discharged.
As described above, in Comparative Examples 1 to 18, since the conditions in the hot metal desiliconization method of the present invention are not satisfied, even if dephosphorization treatment is performed as usual by those skilled in the art after desiliconization treatment, [P] of the hot metal is determined. It could not be made 0.020% by mass or less of the standard condition value.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Converter type refining furnace 2 Hot metal 3 Furnace opening 4 Upper blowing lance 5 Chute 6 Hot water outlet 7 Refractory lance

Claims (1)

When performing desiliconization and dephosphorization of hot metal using the same converter-type refining furnace,
After setting the upper space volume in the converter-type refining furnace after charging the hot metal to 0.2 to 0.6 m ³ / t, CaO-based flux is added to make the slag basicity 0.7 to 1.0, 2 to 3 times the amount of oxygen necessary for desiliconization is supplied by a solid oxygen source and gaseous oxygen, and the average oxygen supply rate of the solid oxygen source at the time of supply is 0.8 to Desiliconization treatment is performed at least once with 2.5 kg-O / t / min and an average oxygen supply rate of the gaseous oxygen of 0.9 to 1.4 Nm ³ / t / min. The amount of decrease is 0.4 to 0.6% by mass,
By passing through the desiliconization treatment, the silicon concentration of the hot metal before the dephosphorization treatment is 0.4% by mass or less,
A hot metal desiliconization method, wherein after the desiliconization process is completed, the dephosphorization process is continued without exhausting the desiliconization slag by tilting the converter-type refining furnace.

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