JP2001172710A - Hot-treating method of molten slag produced at decarburization of molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot-treating technique of molten slag in which the sensible heat of molten slag left in a refining furnace and the sensible heat and the iron content of molten iron left in the refining furnace can profitably be recovered, in a steel tapping work after completing the decarburization of molten iron. SOLUTION: The decarburization is applied to the molten iron 2 pretreated for low phosphorization in a converter 3 and the obtained molten steel is tapped off and the molten slag 5' left in the converter 3 at the tapping-off is directly discharged into a molten iron ladle 9 in which the molten iron 7 is separately held. The molten slag 5' held into the molten iron ladle 9 and the above molten iron 7 held beforehand in it, are charged into a converter type dephosphorizing furnace 10, and the dephosphorizing treatment is applied to the molten iron 7 charged in this dephosphorizing furnace 10. In the above method, the molten iron ladle 9 is utilized as the dephosphorizing furnace as it is. Further, when the molten slag 5' is discharged into the molten iron ladle 9, the molten iron 4' left in the converter 3 is discharged into the molten iron ladle 9 together with the molten slag 5' and thereafter, the treatment is carried out as the same way as the above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating slag generated at the time of decarburizing hot metal, and to dephosphorizing and refining the molten slag at a high temperature without lowering the temperature of the molten slag at an intermediate stage. It is related to technology used as slag for vehicles.

[0002]

2. Description of the Related Art Technical developments for high quality requirements and low price requirements for various steel materials are being made in various places in the steel manufacturing process. In the tapping operation after refining in the steelmaking smelting furnace, the refining process is performed in order to prevent the impurity components transferred and separated from the molten metal into the molten slag during the refining from returning to the metal phase in the subsequent processing steps. The molten slag produced in the above is operated so as not to mix with the molten metal as much as possible in a steel receiving container such as a hot metal ladle or a ladle. That is, in the tapping operation from the refining furnace, the molten metal is discharged from the refining furnace as much as possible to the molten metal holding vessel, while the molten slag is operated to remain in the refining furnace as much as possible. Therefore, there is a problem in how to effectively treat the molten slag remaining in the refining furnace. Further, since it is impossible to completely separate the molten metal and the molten slag in the tapping operation, a small amount of the molten metal remains as a molten metal in the refining furnace after the tapping. Therefore, effective treatment of the molten metal remaining in the furnace is also desired.

[0003] Conventionally, in a method of utilizing slag generated in a decarburizing furnace for hot metal, in particular, for molten slag generated by decarburizing low-phosphorus hot metal subjected to hot metal pretreatment, for example, Japanese Patent Laid-Open No. 3-115515 The use method is disclosed in Japanese Patent Publication No. According to this, the decarburized slag generated when the low-phosphorus hot metal is decarburized is once collected, treated, and added to a converter type dephosphorizer, and newly added during the dephosphorization. The aim is to reduce the amount of slag-making material and promote slagging (hereinafter referred to as prior art).

[0004]

However, in the above-mentioned technology, since the molten slag remaining in the decarburization furnace is once recovered and used after crushing, the heat component of the slag is recovered. It has not been. In addition, when the molten slag is discharged from the decarburization furnace, the molten steel (molten metal) remaining in the decarburization furnace together with the molten slag is discharged to the outside of the refining process system for processing. Is one of the causes.

[0005] The present invention has been made to solve the above problems, and an object thereof is to provide a sensible heat of molten slag remaining in a smelting furnace in a tapping operation after a decarburization process of hot metal, and It is another object of the present invention to provide a method for hot-treating molten slag generated during hot metal decarburization, which can advantageously recover the sensible heat and iron content of molten metal remaining in a refining furnace.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted the following studies from the above viewpoints, and have obtained the following findings. In other words, in order to use the sensible heat of the molten slag remaining in the refining furnace with high efficiency during tapping after the decarburization treatment of the hot metal, the molten slag is used in the latest heat refining while maintaining the high temperature state. Is effective. For that purpose, it is desired that the molten slag (hereinafter, referred to as “decarburized slag”) effectively acts in the refining of the latest heat also in terms of the component composition. Thus, it is necessary that both the thermal treatment operation of the decarburized slag and its component composition are appropriate.

[0007] In order to satisfy such requirements, the hot metal to be subjected to the decarburization treatment has a phosphorus concentration of 0.030 watts.
t. % Or less of the pretreated hot metal whose phosphorous content has been reduced to about% or less. Here, a dephosphorized slag having a low phosphorus concentration is generated, and is used as a part of the slag for the dephosphorization treatment. Moreover, the decarburized slag left in the processing furnace during tapping after decarburization processing is
This is used for the latest heat as a molten slag, and in order to make maximum use of the sensible heat possessed by the slag, the nearest target heat is preferably a treatment heat for dephosphorization. Therefore, the decarburized slag in the molten state is discharged directly to the container in which the hot metal to be dephosphorized is stored, and then the hot metal to be dephosphorized together with the decarburized slag stored in the container,
Promptly subject to dephosphorization. By doing so, it has been found that the sensible heat of the molten slag after the decarburization treatment of the hot metal can be efficiently recovered. Further, they found that if the molten metal remaining in the decarburization smelting furnace was treated together with the molten slag, both the sensible heat and the iron content could be advantageously recovered.

[0008] The present invention has been made based on the above findings, and the gist thereof is as follows. The hot treatment method of molten slag generated at the time of hot metal decarburization treatment in the first invention is to charge the low-phosphorization-treated hot metal into the converter in the pretreatment process of the hot metal, perform decarburization treatment on the hot metal, The obtained decarburized molten steel is tapped from the converter, and the molten slag generated in the decarburization process left in the converter at the time of tapping is transferred to a hot metal holding vessel containing a separate hot metal. The molten slag contained in the hot metal holding vessel and the separate hot metal previously stored in the hot metal holding vessel are charged into another dephosphorization furnace, and then charged into the converter type dephosphorization furnace. The above-described separate hot metal is subjected to a dephosphorization treatment. At this time, the other dephosphorization furnace is not particularly limited as long as it is a furnace capable of dephosphorization, but for example, a converter type vessel is suitable.

In a second aspect of the present invention, a method for hot-treating molten slag generated during hot-metal decarburization processing comprises charging a low-phosphorization-treated hot metal into a converter in a hot-metal pretreatment step and subjecting the hot metal to decarburization processing. The decarburized molten steel obtained is subjected to tapping from the converter, and the molten slag generated in the decarburization process remaining in the converter at the time of tapping is separated from the molten iron containing molten hot metal separately. The molten metal is discharged directly to a holding vessel, and the molten metal slag thus accommodated and the separately accommodated molten iron previously contained are used as a dephosphorization furnace, and the separate molten iron is subjected to dephosphorization. It has.

The hot treatment method for molten slag generated during hot metal decarburization in the third invention is described in the first invention or the second invention.
In the invention, when discharging the molten slag generated in the decarburization process from the converter to the hot metal holding vessel,
It is characterized in that the molten steel remaining in the converter is discharged to the hot metal holding vessel together with the molten slag. Here, the shape of the hot metal holding container is not limited to a hot metal pot, a torpedo, and the like, but a pot-shaped container is preferable for industrial implementation.

[0011]

Next, the present invention will be described with reference to the drawings. FIG. 1 shows a schematic flow illustrating the method for treating molten slag of the present invention. The hot metal 2 which has been subjected to the low-phosphorization treatment in the hot metal pretreatment step 1 is charged into a converter 3 for decarburization treatment and subjected to decarburization treatment. The molten steel 4 after the decarburization process is
From the ladle 11. At this time, the molten slag 5 generated during the decarburization treatment is left while leaving as much as possible in the converter 3 for tapping. After the tapping is completed, in the prior art, the molten slag 5 ′ remaining in the converter 3 is discharged into the slag pan 6, but in the present invention, the residual molten slag 5 ′ in the converter 3 is separated from the molten iron 7 Directly discharges into the hot metal pot 9 whose surface is covered with the heat insulating material 8 to ensure the sensible heat of the residual molten slag 5 ′ in the hot metal pot 9. Further, at this time, all of the small amount of molten steel (residual molten steel) 4 ′ remaining in the converter 3 is transferred to the hot metal pot 9 together with the residual molten slag 5 ′. The residual molten slag 5 ′ and the residual molten steel 4 ′ thus transferred to the hot metal pot 9 and the hot metal pot 9
All of the separate hot metal 7 and heat insulating material 8 previously stored in the furnace are charged into the converter type dephosphorization furnace 10. Converter type dephosphorization furnace 1
A dephosphorization treatment is applied to the entire molten metal (separate hot metal 7 + remaining molten steel 4 ') charged to 0.

In the above process, the hot metal pot 9 containing the hot metal 7 separately may be used as a refining furnace instead of the converter type dephosphorization furnace 10. However, in this case, the hot metal pot 9
Is limited to those which can withstand the dephosphorization treatment.

In the molten slag processing step, the P concentration in the hot metal 2 after the low-phosphorization treatment in the hot metal pretreatment step 1 is 0.030 wt. % Is desirable. When decarburization such low P hot metal 2 in the converter 3, P concentration endpoint P concentration i.e. residual molten slag 5 'in the resulting molten slag (decarburization slag) 5 is a P ₂ O ₅ concentration in terms,
0.07 wt. % Or less. Since the decarburized slag having an extremely low P concentration is used as a part of the dephosphorization slag in the next converter type dephosphorization furnace 10, in the hot metal dephosphorization treatment, P in the molten steel at the end of refining is used.
The concentration can be efficiently and inexpensively reduced to the target value.

In this way, the dephosphorized hot metal is decarburized,
The decarburized slag produced here is used hot for part of the slag used in the dephosphorization refining, and the molten metal is also used hot in the dephosphorization refining. The effect, reduction of the amount of additional slag, and recovery of the iron source are possible.

[0015]

EXAMPLES The present invention will be further described with reference to examples.

The following test was conducted according to the processing flow of the present invention shown in FIG. [P] = 0.020 wt. %
The decarburization refining was performed in the 300 t converter 3 using the pretreated hot metal 2 of the above. The molten steel 4 discharged into the ladle 11 was conveyed to the secondary refining or casting process of the next step and processed as usual. On the other hand, the converter 3 after the end of the tapping operation
About 4 t of the molten slag 5 ′ and about 2 t of the molten metal 4 ′ remained therein. In the normal operation, these residues in the converter are taken out of the system of the refining process, for example, into the slag pan 6, and subjected to slag treatment and metal processing. On the other hand, in the test of the embodiment of the present invention, the entire amount of the molten slag 5 'and the molten metal 4' remaining in the converter 3 is immediately stored in the molten iron 7 separately, and the dephosphorization in the next step is performed. It was discharged to the hot metal ladle 9 waiting for the treatment step. Thus hot metal pot 9
The entire amount of the contents (metal and slag) in the standby hot metal pot 9 to which the newly added molten slag 5 ′ and about 2t of molten slag 5 ′ are added into the dephosphorization furnace 10. hand,
Dephosphorization refining was performed. A 300 t converter type dephosphorization furnace 10 was used for the dephosphorization treatment. The operating conditions for dephosphorization refining were set within the range of normal processing conditions.

As described above, when the molten slag and molten metal remaining in the 300-ton converter 3 after the completion of the tapping operation after the decarburization refining is used as the hot charging material for the dephosphorization furnace. In order to evaluate the effectiveness of the above, the following normal operation heat was used as a comparative example. That is, in the heat of the comparative example, the molten slag remaining in the converter and the remaining hot water in the converter after the tapping from the decarburizing smelting furnace as in the above-described embodiment is used as the hot charging material for the dephosphorization furnace. The slag treatment and the slag treatment were performed by taking out the slag treatment and the metal slag as usual.
Then, the hot metal accommodated in the hot metal pot was charged into the 300t converter type dephosphorization furnace as usual, and dephosphorization refining was performed.

The difference in the test conditions between the working example and the comparative example is that only the hot charging of the residual slag and the metal in the decarburizing furnace to the above-mentioned dephosphorizing furnace is carried out. No differences in test conditions were set. However, the amount of CaO charged was appropriately adjusted according to the amount of hot slag remaining in the decarburization furnace. The main operating conditions for dephosphorization refining are as follows. Hot metal temperature in hot metal pot: 1270 to 1320 ° C Hot metal in hot metal pot [P]: 0.100 to 0.120 wt. % Endpoint temperature: 1280 to 1330 ° C. Endpoint molten steel phosphorus concentration [P]: 0.005 to 0.030 wt. % Terminal slag basicity (CaO / SiO2): 3.5 to 4.5 Fe: 5.0 to 10.0 wt. %

The test results are as follows. FIG.
The purpose of the present invention is to compare the embodiment and the comparative example with the progress of the dephosphorization in the dephosphorization refining using the P distribution between the slag and the metal at the end point of the refining as an index. The horizontal axis, de-P of the molten steel is P oxidation reaction: 2 P +5 O +4 (CaO ) = (4C
aO · P ₂ O ₅ ), assuming that a chemical equilibrium is established between the molten steel and the slag, using the measured values of the P concentration and the O concentration (wt.%, the same applies hereinafter) in the molten steel. It is the ratio of the calculated P ₂ O ₅ concentration in slag (P ₂ O ₅ ) _cal to the measured value of P concentration in molten steel [P] _anl , and the vertical axis is P ₂ O _{5 in} slag.
It is the ratio of the measured value (P ₂ O ₅ ) _anl of the concentration to the measured value [P] _anl of the P concentration in the molten steel.

According to the figure, the concentration of P ₂ O ₅ in the molten slag is closer to the chemical equilibrium value in the example than in the comparative example. This is because, in the example, the slag was more effectively used than in the conventional method because the sensible heat was effectively used as the slag holding heat at the time of dephosphorization refining due to the hot treatment operation of the residual slag mainly in the decarburization furnace. As a result, it can be seen that the dephosphorization treatment was performed quickly.

FIG. 3 shows the average S in the hot metal charged to the dephosphorization furnace.
i concentration [Si] and the total lime weight T.C. It is a graph which compares the relationship with CaO (kg / t- molten steel, hereafter the same) about an Example and a comparative example.

According to the figure, the total weight T.M. CaO shows that in Examples, it was about 70% less than that of Comparative Examples. This is because in the example, the amount of lime to be newly charged was good because of the contribution of the additional charging of the residual molten slag in the decarburization furnace to the dephosphorization furnace. From this result, it can be seen that, in the method of the present invention, the basic unit of the slag-making material to be newly added is also reduced in the slag-making material other than lime as compared with the conventional method.

Further, in the embodiment, by adding the residual molten metal in the decarburizing furnace to the dephosphorizing furnace, the weight of tapping from the dephosphorizing furnace is increased, the tapping yield is improved, and Reduction of oxygen gas required for dephosphorization blowing by adding sensible heat of ingots and residual molten slag, and improvement of steel production yield by increasing iron ore input during dephosphorization refining, and T. The effect of suppressing the oxidation of the molten iron by the Fe concentration was observed.

[0024]

As described above, according to the present invention,
The sensible heat of the molten slag and the sensible heat of the molten metal produced in the decarburization and refining of hot metal can be used to the fullest extent. Steel yield is improved. It is possible to provide a method for hot-treating molten slag generated during hot metal decarburization, in which such effects are exerted, and industrially useful effects are brought about.

[Brief description of the drawings]

FIG. 1 is a schematic flowchart illustrating a method for treating molten slag of the present invention.

FIG. 2 is a graph comparing the example of P distribution between slag and metal in dephosphorization refining with the comparative example.

FIG. 3 is a graph comparing the relationship between the Si concentration in the hot metal charged in the dephosphorization treatment and the amount of newly added total lime between the example and the comparative example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 hot metal pretreatment step 2 hot metal 3 converter 4 molten steel 4 ′ residual molten steel 5 molten slag 5 ′ residual molten slag 6 slag pan 6 7 separate hot metal 8 heat insulator 9 hot metal ladle 10 converter type dephosphorizing furnace 11 ladle

Claims (3)

[Claims] Claims 1. A hot metal that has been subjected to a low phosphorous treatment in a hot metal pretreatment step is charged into a converter, subjected to decarburization treatment, and the resulting decarburized molten steel is discharged from the converter, The molten slag generated in the decarburization process left in the converter at the time of tapping is directly discharged to a hot metal holding vessel containing separate hot metal, and thus the molten slag stored in the hot metal holding vessel is obtained. The slag and the separate hot metal previously stored in the hot metal holding vessel are charged into another dephosphorization furnace, and the dephosphorization is performed on the separate hot metal charged into the dephosphorization furnace, A hot treatment method for molten slag generated during hot metal decarburization. 2. A hot metal that has been subjected to a low phosphorous treatment in a hot metal pretreatment step is charged into a converter, subjected to decarburization treatment, and the resulting decarburized molten steel is discharged from the converter, The molten slag generated in the decarburization process left in the converter at the time of tapping is directly discharged to a hot metal holding vessel containing a separate hot metal, and the molten slag thus stored and the molten slag stored beforehand are stored. A method for hot-treating molten slag generated during hot metal decarburization, wherein the hot metal holding vessel containing the hot metal separately is used as a dephosphorization furnace and the hot metal is dephosphorized. 3. When the molten slag generated in the decarburization process is discharged from the converter to the hot metal holding vessel, the molten steel remaining in the converter together with the molten slag is stored in the hot metal holding vessel. 2. The method according to claim 1, wherein
Or a hot treatment method for molten slag generated during the hot metal decarburization treatment according to 2.