JP2011246743A - Method of hot metal dephosphorization treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of hot metal pre-dephosphorization using a converter, capable of achieving high-speed oxygen feeding treatment while simultaneously suppressing both generation of spitting and dust and generation of slopping, and further capable of obtaining high dephosphorization ability.SOLUTION: In a method of hot metal dephosphorization treatment, a top and bottom blowing converter is used, and a top-blowing oxygen is sprayed to a hot metal in the converter. A top-blowing oxygen feed rate is set to 2.5-4.0 Nm/min per ton of hot metal during the dephosphorization treatment, and a powdered recarburizing agent in an amount of 1.5-5.5 kg/t in terms of C amounts is sprayed from a sub-lance after at least one of decarburization slag and ladle slag is input in the converter as a slag formation agent.

Description

  The present invention relates to a method for preliminarily dephosphorizing hot metal using a converter with high efficiency and high efficiency.

  In recent years, the entire steelmaking process has been remarkably improved in efficiency and efficiency, and high efficiency and high dephosphorization ability are strongly demanded in hot metal dephosphorization treatment. In order to meet this demand, the hot metal dephosphorization reaction is a reaction that oxidizes phosphorus (P) in the hot metal and shifts it to slag, so it generates oxygen source and slag to oxidize phosphorus and absorbs phosphorus. It is necessary to speed up the supply of the CaO source in order to adjust the slag composition by hatching the CaO source in as short a time as possible. However, it is generally difficult to sufficiently hatch the CaO source in a short time, and poor dephosphorization tends to be a problem. Further, when the oxygen supply rate is increased, slopping, spitting and the like are likely to occur.

  Conventionally, hot metal dephosphorization has been effective in achieving a dephosphorization rate of 80% or more at an oxygen supply time of about 10 minutes at a low temperature of about 1300 to 1400 ° C. However, in most cases, it was necessary to use a lot of hatching accelerators such as fluorite for promoting the hatching of the CaO source.

  However, in recent years, the effective use of steelmaking slag, including slag after hot metal dephosphorization, has come to be emphasized, and in order to increase its effective utilization rate, there is a demand when using slag for civil engineering materials and roadbed materials. It is necessary to consider. As a result, the use of fluorite is virtually impossible. Therefore, there is an increasing need for a technique for reducing as much as possible the concentration of un-enriched CaO (f. CaO) in the slag after treatment without using fluorite.

Therefore, in recent years, as in the invention described in Patent Document 1, for example, a method of pulverizing a CaO source and spraying it on hot metal together with oxygen from an upper blowing lance has come to be used. Further, in the slag after dephosphorization treatment f. In order to further reduce CaO, a method of using Al ₂ O ₃ -containing slag such as ladle slag as a hatching accelerator instead of fluorite is also being used.

However, in the invention described in Patent Document 1, the upper blowing oxygen flow rate per 1 ton of molten iron is 0.5 to 2.0 Nm ³ / min, and the dephosphorization blowing time is 7 to 10 minutes. Recently, even this amount of processing time has become too long and has become insufficient. In order to further shorten the dephosphorization blowing time, it is necessary to further increase the supply flow rate of the top blown oxygen and accelerate the hatching of the CaO source.

In the method of the invention, in order to promote the hatching of the CaO source, the CaO source is pulverized and sprayed onto the molten iron together with oxygen from the top blowing lance. However, in general, spitting increases only by increasing the oxygen supply rate. In this method, since the supply rate of the powdered CaO source is increased simultaneously with oxygen, it is natural that the spitting becomes more severe. is expected. Therefore, in order to avoid the problem, it is conceivable to reduce the ratio of the powdered CaO source supplied from the top blowing lance and supply it separately by supplying a massive CaO source from above the converter. Delay in hatching of CaO source supplied in a lump, resulting in poor dephosphorization and f. The problem of increasing CaO occurs. As a countermeasure, when the supply amount of the Al ₂ O ₃ source such as ladle slag is increased, problems such as slag forming easily and slopping appear.

As described above, there are many problems related to the high efficiency and high dephosphorization ability of the hot metal dephosphorization process, and they are related to each other, so that the comprehensive solution of these problems is not easy. Therefore, in the invention described in Patent Document 2, first, a ladle slag is added to generate cover slag on the hot metal, and then a powdered CaO source is sprayed together with oxygen from an upper blowing lance, so that the spitting amount Has been successfully reduced. However, since it is explained that the flow rate of the top blown oxygen in this invention is preferably 0.5 to 2.5 Nm ³ / min per 1 ton of hot metal, it is understood that a certain degree of efficiency has been achieved. In this method, the time for blow-on powder blowing, which is the original dephosphorization process, is limited, and it is considered that there remains room for further improvement in efficiency.

  Moreover, although the method of utilizing ladle slag for cover slag production | generation is described in patent document 2, the hatching acceleration | stimulation and slopping prevention and utilization method of ladle slag when the oxygen flow rate is accelerated are described. There is no description or suggestion about the relationship.

On the other hand, Patent Document 3 describes a method in which an appropriate amount of cover slag is generated in advance by performing a hot metal desiliconization process of about 0.05% before charging the hot metal into the hot metal dephosphorization furnace. . In this method, when the oxygen top blowing time is 9 minutes in total and the cover slag generation processing time without powder CaO is shortened to 1 minute, the top blowing oxygen flow rate is 1.4 Nm ³ / t of hot metal. It is explained that no spitting was observed at min. However, there is no description at all regarding the problems and effects relating to the hot metal dephosphorization treatment by shortening the oxygen top blowing time and the solution to the problems.

Patent Document 4 discloses that the slag basicity (= mass ratio [% CaO /% SiO ₂ ], the same applies hereinafter) is set to 1.0 or more and less than 2.5 to promote the hatching of the CaO source, and the acid feed rate. Describes a hot metal dephosphorization method that can prevent spitting and an increase in the amount of dust generated even if it is 1.5 to 5.0 Nm ³ / min / t. In the specification, it is explained that when the basicity of slag is simply lowered, the dephosphorization ability is lowered, and the dephosphorization ability is supplemented by increasing the oxygen delivery rate by increasing the acid feed rate, It is described that the dephosphorization reaction can be promoted efficiently by spraying a granular refining agent or solid oxygen source onto the molten iron together with gaseous oxygen. That is, this method is understood to increase the FeO concentration instead of decreasing the basicity of the slag.

  However, in this method, low basicity and high (T.Fe) slag is formed, so that slag forming is promoted, and there is a concern that the frequency of slapping increases. In addition, when dephosphorization treatment is performed by spraying the powdery refining agent from the top blowing lance to the hot metal using oxygen as a carrier gas, spitting tends to increase as described in Patent Documents 2 and 3, and some device is used. Although it is considered necessary, Patent Document 4 does not explain such a device.

Japanese Patent No. 3557910 Japanese Patent No. 3687433 Japanese Patent No. 4196997 JP 2008-266666 A

  Accordingly, the object of the present invention is to solve the above-mentioned problems of the prior art and achieve high-speed acid feeding treatment while achieving both suppression of spitting and dust generation and generation of slopping, and further high dephosphorization ability. It is an object of the present invention to provide a converter type hot metal preliminary dephosphorization method capable of obtaining the above.

In order to realize an increase in the acid feed rate while suppressing the amount of spitting and dust generation, it is necessary to take measures to promote hatching of the added CaO source.
Therefore, the present inventors conducted a test to add an acid feed rate of 2.5 Nm ³ / min / t or more while adding decarburization slag and ladle slag, and added the powdered carburizing agent and dephosphorization treatment at that time. The relationship between slag hatching, spitting, dust generation, slopping and dephosphorization was investigated and elucidated as follows.

  (1) The decarburization slag or ladle slag is introduced into the converter at an early stage during the dephosphorization treatment time (upblowing oxygen supply time), and then the powdered carburizing agent is sprayed from the sub lance. Since the heat of combustion of the charcoal reaches the slag and forms molten slag at an early stage, cover slag can be formed on the hot metal over the entire period of supplying the top-blown oxygen, thereby suppressing the occurrence of spitting. it can.

(2) T. in excess slag by blowing a carburizing agent. Reducing Fe; Occurrence of slopping can be suppressed by the effect of controlling the Fe concentration within an appropriate range.
(3) Finally, the slag hatchability can be kept at a high level. By controlling the Fe concentration within an appropriate range, the phosphorus concentration in the hot metal can be made sufficiently low.

From this, the gist of the present invention is defined as follows.
(1) A method of using a top-bottom blowing type converter and spraying top blowing oxygen onto the hot metal in the converter to dephosphorize the hot metal, and during the dephosphorizing treatment, the supply rate of top blowing oxygen is increased. and less hot metal per tonne 2.5 Nm ³ / min or more 4.0 nm ³ / min, and at least one of the decarburization slag and ladle slag as slag forming agent after switching on the said transfer furnace, powdery additive from sub-lance A hot metal dephosphorization method, characterized by spraying a charcoal agent in an amount of 1.5 kg / t to 5.5 kg / t in terms of C mass.

According to the present invention, by setting the upper blowing oxygen flow rate to 2.5 to 4.0 Nm ³ / min / t, the supply time of the upper blowing oxygen in the dephosphorization process is enhanced to 3.0 to 5.0 minutes. Further, the hot metal dephosphorization rate of 90% or more is achieved while suppressing the generation of spitting, dust and slopping, and the unsaturated CaO concentration in the slag after treatment is 5% by mass or less. A highly efficient and highly efficient hot metal dephosphorization process can be performed.

It is a graph showing the influence of the decarburization slag, the ladle slag, and the powdered carburizing agent on the relationship between the top blowing oxygen flow rate and the dephosphorization rate. It is a graph showing the influence of the decarburization slag, the ladle slag, and the powdered carburizing agent on the relationship between the top blowing oxygen flow rate and the spitting level. It is a graph showing the influence of the decarburization slag, the ladle slag, and the powdered carburizing agent on the relationship between the flow rate of the top blown oxygen and the concentration of unoxidized CaO in the slag. It is a graph showing the relationship between the amount of spraying of a carburizing agent and the un-foamed CaO concentration in slag in the survey condition B.

In the present invention, spraying the hot metal to oxygen from the top lance at a flow rate of hot metal per tonne 2.5Nm ³ /min~4.0Nm ³ / min. The purpose of the present invention is to perform the top blowing oxygen in a short time of 5 minutes or less. Therefore, considering combustion of the powdered carburizing agent, at least 2.5 Nm ³ / min per ton of hot metal. This is because it is impossible to achieve this goal unless stable operation is achieved. However, if it exceeds 4.0 Nm ³ / min, it will be difficult to control slag generation even with the present invention as described later, resulting in a decrease in the dephosphorization rate and an increase in the occurrence of spitting / slipping, The stable operation cannot be performed.

  Further, in the present invention, decarburization slag and ladle slag are used as slag generating agents in order to generate cover slag on the hot metal at an early stage of dephosphorization treatment and to promote melting and hatching of a separately supplied CaO source. At least one of them.

The decarburized slag is slag remaining in the converter after completion of decarburization, which is the next step of the hot metal dephosphorization treatment, and has a composition in the range shown in Table 1 in general. The ladle slag is slag remaining in the ladle after the end of continuous casting, and has a composition in the range shown in Table 2 in general. In these tables, all percentages indicating concentrations are mass%. Among these compositions, in particular, the Al ₂ O ₃ concentration and T.I. The Fe concentration is important for lowering the melting point of the slag to increase its melting property and keeping the melting point of the slag in the converter during the dephosphorization process low.

  Since one of the purposes of introducing decarburized slag and ladle slag is to generate cover slag on the hot metal at an early stage, the injection as the slag generating agent requires that the blowing time of top blowing oxygen It is preferable that 30% of the time elapses. The charging method may be to batch-charge the oxygen into the converter before starting the spraying of top-blowing oxygen using a scrap chute, or to blow the top-blowing oxygen from a bunker installed on the converter. You may divide | segment into a converter appropriately during attachment.

  The size of decarburized slag and ladle slag may be crushed cold slag, but hot slag is thrown into the converter using a scrap chute and slag hatching and heat loss occur. It is preferable from the viewpoint of reduction.

There is also a method of adding a carburizing agent as a secondary material for refining from a bunker installed above the converter, but the size of the carburizing agent is large and the hot metal is stirred deeply into the hot metal by hot-blowing oxygen. Although there is an effect of increasing the carbon concentration of the slag and serving as a heat source, the effect of accelerating the hatching due to heat on the slag cannot be obtained. Therefore, it is necessary to spray the powdered carburizing agent from the sublance. Since the purpose of carburizing in the present invention is to promote melting and melting of the added CaO source, the use of a powdered carburizing agent improves the efficiency of heat application to the slag by burning it to CO ₂ as much as possible in the slag layer. Suitable for Therefore, the addition position of the carburizing agent (exit position from the sub lance) is preferably in the slag layer 1 m or more away from the hot metal bath surface. The timing of adding the carburizing agent needs to be performed after charging at least one of the decarburized slag and the ladle slag in order to promote hatching of the added CaO source. Considering mainly that the introduction of these slags is for the purpose of promoting the hatching of the added CaO source, the addition of the carburizing agent achieves its purpose when the decarburization slag and ladle slag in the treatment are completed. Therefore, it can be said that it is more preferable.

  As the type of the carbonizing agent, coke having a mass concentration of carbon of 85% or more and soil graphite are suitable, and the particle size is preferably 1 mm or less in order to accelerate combustion. The addition amount needs to be 1.5 to 5.5 kg in terms of C mass per 1 ton of hot metal. If the amount is less than 1.5 kg per 1 ton of hot metal, the effect of burning the charcoal and igniting the slag is not clear. On the other hand, if it exceeds 5.5 kg per 1 ton of hot metal, the amount of oxygen required for the combustion becomes too much. This is because it is not suitable for performing the dephosphorization treatment in a short time as in the present invention, and the possibility of operation hindrance due to slag forming or slag scattering increases.

  In the present invention, due to the above-mentioned various requirements, the cover slag is generated on the hot metal immediately after the start of the supply of the top blown oxygen, and the generation of spitting / slipping is suppressed, and the treatment is as short as 3.0 to 5.0 minutes. The hot metal dephosphorization rate is 90% or more over time, and the uncontained CaO mass concentration in the slag after treatment is 5% or less.

Therefore, as the slag composition, _Al 2 _{O 3} concentration 3-10 wt% and T. It is desirable that Fe is 3 to 15% by mass. By controlling the slag composition in this way, it becomes easy to melt and melt the CaO source, and an effect of suppressing spitting can be expected.

  It should be noted that the hot metal temperature at the end of the blowing of the upper blown oxygen is better in the sense that it promotes the melt hatching of the CaO source and increases the reactivity of the slag, while the dephosphorization ability of the slag is lower. It is well known that is generally preferred. In the present invention, it is preferable to control the hot metal temperature at the end of the blowing of the top blown oxygen to about 1350 to 1400 ° C. by giving priority to promoting the melt hatching of the CaO source and increasing the reactivity of the slag.

Conventional conditions (do not use decarburization slag and ladle slag), survey conditions A (use at least one of decarburization slag and ladle slag), investigations on decarburization slag and ladle slag according to the present invention Condition B (using at least one of decarburized slag and ladle slag and spraying soil graphite as a powdered carburizing agent from 0.5 to 5.5 kg / t sub lance in terms of C mass) The flow rate of blown oxygen was compared in the range of 1.3 to 4.3 Nm ³ / min per ton of hot metal, and the effect of the invention specific requirement according to the present invention was confirmed.

The conditions common to this investigation will be explained together.
About 260 t of hot metal discharged from the blast furnace is appropriately desulfurized and desiliconized, and then about 30 t of scrap is charged into an upper-bottom blowing converter equipped with a powdered CaO supply function. The furnace was charged. The hot metal component was C: 4.0-4.8%, Si: 0.15-0.51%, Mn: 0.20-0.40%, P: 0.090-0.130%, S : 0.003 to 0.03%.

Hot metal to erect the Tenro the _{N 2} while flowing in a range of hot metal per tonne 0.15~0.25Nm ³ / min as bottom-blown gas after charging, insert the top lance immediately converter furnace, The top blowing oxygen was started to be sprayed onto the hot metal in the range of 1.3 to 4.3 Nm ³ / min per ton of hot metal. This oxygen flow rate was constant during each treatment in this study. Simultaneously with the start of the spraying of the top-blown oxygen, powdered quicklime having a particle size of 0.1 mm or less was started to be sprayed on the hot metal together with the oxygen. The spraying of oxygen was completed in 2.6 to 9.3 minutes depending on the oxygen flow rate, and at the same time, the spraying of powdered quicklime was also completed.

  In this investigation, only the above-mentioned powdered quicklime having a particle size of 0.1 mm or less and at least one of decarburized slag and ladle slag are used as auxiliary materials used for the dephosphorization treatment, and other auxiliary materials are used. I did not.

These inputs are based on the components and amounts used of each raw material including hot metal, and in the survey conditions A and B using at least one of decarburized slag and ladle slag, the slag basicity after treatment is 1.5 to 3.0, the Al ₂ O ₃ concentration in the slag is 3 to 10% by mass; It was determined by calculation so that the Fe concentration was in the range of 3 to 15% by mass. On the other hand, in the conventional conditions in which neither decarburization slag nor ladle slag is used, the slag basicity after treatment is 1.5 to 3.0, and T. Fe concentration was calculated to be in the range of 3 to 15 _wt%, but for the concentration of Al 2 _{O 3} were excluded from the adjustment target.

The chemical composition of used decarburization slag and ladle slag was the same as that shown in Tables 1 and 2.
Table 3 summarizes specific conditions and results of each dephosphorization treatment in this investigation.

The Al ₂ O ₃ concentration in the slag after dephosphorization, which is not described in this table, is 1 to 3% by mass under conventional conditions in which decarburization slag and ladle slag are not used, and decarburization slag and ladle slag In the investigation conditions A and B using the above, both were controlled to 3 to 10% by mass. In addition, T. The Fe concentration was all controlled to 3 to 15% by mass.

No. which is a conventional condition. In 1-5, the dephosphorization rate fell, the spitting increased, and the amount of dust generated increased with an increase in the top blown oxygen flow rate. Since (f.CaO) of the slag after the treatment increased as the flow rate of top blown oxygen increased, it was found that the hatching of the CaO source was deteriorated. In addition, it can be seen that slapping occurs when the top blown oxygen flow rate ≧ 2.0 Nm ³ / min / t under these conditions.

Investigation condition A No. In the case of 6 to 10, the dephosphorization rate was high at the low oxygen flow rate of the top blown oxygen flow rate of 1.4 Nm ³ / min / t, there was no spitting, and the amount of dust generation was small. Since (f.CaO) of the slag after the treatment was low, it can be seen that the hatching of the CaO source was sufficiently advanced. However, when the top blown oxygen flow rate is the same as the conventional conditions, the dephosphorization rate is generally high, and spitting and dust generation tend to be small. A trend was confirmed. In particular, when the oxygen flow rate was 2.0 Nm ³ / min / t or more, spitting was severe and slopping occurred, and the situation was not able to withstand the operation.

Survey condition B No. In Nos. 11 to 20, the carburizing agent top blowing rate is in the range of 1.5 kg / t to 5.5 kg / t (No. 13 to 17), which is better than the conventional conditions. .5Nm ³ / even exceed min / t, it 3.9Nm ³ / min / t until Datsurinritsu, spitting, dust generation amount is maintained at a good level, the processed slag (f .CaO) was also stable at a low level. However, when the addition amount of the carburizing agent is less than 1.5 kg / t (No. 11 and 12), the melting and melting of the refining agent does not proceed sufficiently, and the slag (f. The phosphorus rate was low. Moreover, when there was more carburizing agent addition amount than 5.5 kg / t (No. 18-20), the increase in the amount of oxygen required by the increase in carburizing amount occurred, and the process required 5 minutes or more. Further, since the amount of generated CO gas increased, slapping occurred during the treatment, and it was difficult to continue the operation (Table 3).

As described above, the hot metal dephosphorization treatment at an upper blowing oxygen flow rate of 4.0 Nm ³ / min / t or less is possible, and the treatment time is reduced by 5.0 minutes compared to the case of the upper blowing oxygen flow rate of 1.3 Nm ³ / min / t. Became possible.

  Next, the effect obtained by satisfying the invention specific items according to the present invention will be described using a graph together with the results of the investigation shown in Table 3.

(1) Dephosphorization rate The dephosphorization rate is expressed by the following equation.
Dephosphorization rate = 100 × (before dephosphorization [P] −after dephosphorization [P]) ÷ before dephosphorization [P]
Since the present invention aims at high efficiency and high efficiency of the hot metal dephosphorization treatment, it is a basic matter that can be said to be premised on that the treatment time is short and the dephosphorization rate is sufficiently high.

  It has been found that the time required for the hot metal dephosphorization process is determined by the flow rate of the top blown oxygen per ton of hot metal based on conventional knowledge. Therefore, the relationship between the top blown oxygen flow rate per ton of hot metal to be dephosphorized and the dephosphorization rate is the same as the conventional conditions among the investigation conditions of decarburization slag, ladle slag and powdered carburizing agent. FIG. 1 shows the stratification according to the survey condition B ′ in which the spray amount of the carburizing agent is 1.5 to 5.5 kg / t among the survey condition A and the survey condition B.

In the present invention, the upper blown oxygen flow rate is set to 2.5 Nm ³ / min / t or more. In the investigation condition B ′ that satisfies all the use conditions such as ladle slag according to the present invention, the upper blown oxygen flow rate 2. in 5Nm ³ / min / t or more 4.0Nm ³ / min / t or less of the range, dephosphorization rate seen that had able to maintain more than 90%.

(2) Situation of spitting When the flow rate of top blown oxygen is increased in order to shorten the dephosphorization time, an increase in spitting tends to be a problem, particularly in hot metal dephosphorization method in which a powdered CaO source is blown together with top blown oxygen. . In the present invention, in order to accelerate the melt hatching of the CaO source, dephosphorize in a short time, and to reduce the concentration of the undehydrated CaO contained in the slag after the treatment, the powdered CaO source is sprayed onto the molten iron together with the top blowing oxygen. It is important to suppress the occurrence of spitting.

  The occurrence of spitting can be determined visually. Therefore, the amount of granular iron scattered by spitting was evaluated in four stages of 1 to 4 (the smaller the amount of granular iron scattered, the smaller the numerical value). FIG. 2 shows the relationship between the flow rate of the top blown oxygen per ton of hot metal to be dephosphorized and the spitting level, stratified according to the investigation conditions for decarburization slag, ladle slag and powdered carburizing agent.

In the present invention, the upper blown oxygen flow rate is set to 2.5 Nm ³ / min / t or more. In the investigation condition B ′ that satisfies all the use conditions such as ladle slag according to the present invention, the upper blown oxygen flow rate 2. in 5Nm ³ / min / t or more 4.0Nm ³ / min / t or less of the range, it can be seen spitting level was 1.

(3) Undehydrated CaO concentration in post-treatment slag The basic idea of the present invention is that the treatment time is short and the dephosphorization rate is sufficiently high. However, the amount of CaO required for this purpose increases. If the added CaO is left unreacted in the slag after the treatment, it cannot be said to be an efficient dephosphorization treatment. In addition, if the undehydrated CaO concentration in the slag after treatment exceeds 5% by mass, difficulties arise when trying to use the slag for civil engineering materials, and the efficiency of the entire dephosphorization treatment including the slag treatment is improved. Decreases and costs increase.

  Therefore, the relationship between the flow rate of the top blown oxygen per ton of hot metal to be dephosphorized and the concentration of undehydrated CaO in the slag after treatment was investigated for the decarburization slag, ladle slag and powdered carburizing agent. FIG. 3 shows stratification according to conditions.

In the present invention, the upper blown oxygen flow rate is set to 2.5 Nm ³ / min / t or more. In the investigation condition B ′ that satisfies all the use conditions such as ladle slag according to the present invention, the upper blown oxygen flow rate 2. It can be seen that in the range of 5 Nm ³ / min / t or more and 4.0 Nm ³ / min / t or less, the mass concentration of the non-hatched CaO was 5% or less.

(4) Appropriate amount of carburizing agent In the present invention, at least one of decarburizing slag and ladle slag is introduced into the converter at an early stage during the dephosphorization processing time, and then the powdered carburizing agent from the sub lance. , The combustion heat of the carburizing agent is applied to the slag, the molten slag is formed at an early stage, and the supply rate is 2.5 to 4.0 Nm ³ / min / molten ton during the upper blowing oxygen supply Suppresses the occurrence of spitting.

Furthermore, T. in excess slag by blowing in the carburizing agent. Reducing Fe; The effect of controlling the Fe concentration within an appropriate range suppresses the occurrence of slopping.
At the same time, the hatchability of the slag can finally be kept at a high level. By controlling the Fe concentration within an appropriate range, the phosphorus concentration in the hot metal can be made sufficiently low.

  However, as shown in FIG. 4, when the addition amount of the carburizing agent is less than 1.5 kg / t, the effect of promoting the melting and hatching of the refining agent is not sufficiently exhibited, and the (f. It was increasing. For this reason, the phosphorus removal rate was low (No. 11 and 12).

On the other hand, when the addition amount of the carburizing agent is more than 5.5 kg / t, the increase in the amount of carburizing causes an increase in the oxygen supply amount necessary for the oxidation, and the upper blown oxygen flow rate is 2.5 Nm ³ / min / t or more 4 Even under the condition that the condition of 0.0 Nm ³ / min / t or less was satisfied, the dephosphorization process took 5 minutes or more. Moreover, since CO gas generation amount increased, slapping generate | occur | produced during the process and it was difficult to continue operation (No. 18-20).

  Therefore, in the present invention, at least one of the decarburized slag and ladle slag is introduced into the converter so as to satisfy the predetermined post-treatment slag component at an early stage during the dephosphorization treatment time, and then the powder from the sub lance. It is important to spray the carburizing agent in the range of 1.5 to 5.5 kg / t.

Claims (1)

A method of dephosphorizing the hot metal by using a top-bottom blowing type converter and spraying top-blown oxygen onto the hot metal in the converter,
The feed rate of top-blown oxygen and less hot metal per tonne 2.5 Nm ³ / min or more 4.0 nm ³ / min during dephosphorization,
And,
After charging at least one of decarburized slag and ladle slag as a slag generator into the converter,
A method of dephosphorizing hot metal, characterized in that a powdered carbonizing agent is sprayed from a sub lance to 1.5 kg / t or more and 5.5 kg / t or less in terms of C mass.

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