JP3458890B2 - Hot metal refining method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot metal refining method, and more particularly to a refining method for highly efficiently performing dephosphorization treatment of hot metal.

[0002]

2. Description of the Related Art Conventionally, in the converter steelmaking method, dephosphorization refining and decarburization refining of hot metal have been carried out in the same converter. However, in recent years, as the demand for steel quality has increased, with the expansion of continuous casting, the secondary refining of molten steel such as vacuum degassing and ladle refining, etc., has spread, the tapping temperature in the converter rises, The dephosphorization capacity in the converter has decreased. This is because the higher the hot metal temperature, the lower the dephosphorization efficiency.

Under such a background, a hot metal pretreatment method has been developed in which the hot metal is preliminarily refined, and in particular, phosphorus components are removed to some extent and then charged into a converter. In this method, it is usual to perform dephosphorization refining of the hot metal by using a hot metal ladle, a converter type container, etc., and move the dephosphorized hot metal to another converter to perform decarburization refining. In Japanese Examined Patent Publication No. 2-14404 and Japanese Examined Patent Publication No. 3-77246, one of two converter-type vessels having both upper and lower blowing functions is used as a dephosphorization furnace, and the other is used as a decarburization furnace. A method of refining hot metal under the conditions of 1 has been proposed.

[0004]

However, in such dephosphorization refining of hot metal, a certain slag volume is required, and since it is a low-temperature operation as compared with decarburization blowing, the slagging efficiency of the smelting material is also high. However, there is a problem that the original dephosphorization efficiency cannot be exhibited as a result, and therefore the dephosphorization treatment time becomes long and the refining cost is unavoidably high. Further, depending on the raw material components such as iron ore, the concentration of impurities such as P may increase during tapping of the blast furnace, and it is necessary to flexibly respond to such changes in the operating conditions on the pig-making side. Also, it occurs in the steelmaking method in which dephosphorization refining of molten pig iron is performed in a refining vessel such as a ladle or converter type vessel, and the dephosphorized refined molten iron is transferred to another converter type vessel for decarburization refining. Although the amount of slag can be reduced as compared with the conventional one, as a recent tendency, further reduction of the amount of steelmaking slag is desired. In this respect, for example, the above-mentioned Japanese Patent Publication No. 2-14404.
Japanese Patent Publication discloses a technique for reducing the amount of slag generated in the entire steelmaking process by using the slag generated in decarburization refining in the dephosphorization refining, but this alone reduces the recent steelmaking slag generation amount. It is not possible to fully meet the demand for conversion.

Therefore, an object of the present invention is to solve the above problems of the prior art and to perform dephosphorization refining using a hot metal ladle or a converter-type vessel before decarburization refining with high efficiency. At the same time, it is to provide a hot metal refining method capable of reducing the amount of steelmaking slag generation and further improving the overall steelmaking efficiency.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have examined the conditions for improving the dephosphorization efficiency in the above-mentioned dephosphorization refining, mainly from the aspects of the hot metal component, the hot metal temperature, and the addition conditions of the medium material. As a result, the amount of Si in the hot metal before the dephosphorization treatment is sufficiently reduced, specifically, the amount of Si is 0.07 wt% or less, preferably 0.05 wt% or less,
It has been found that the dephosphorization efficiency can be dramatically improved as compared with the conventional case by particularly preferably reducing the level to 0.03 wt% or less and performing the dephosphorization treatment on such hot metal. Further, in such a dephosphorization treatment, the hot metal temperature at the start of the dephosphorization treatment and the hot metal temperature at the end of the dephosphorization treatment should be appropriately controlled. It has been found that the dephosphorization efficiency is further improved by supplying it. Further, it was also found that the Si reduction of the hot metal can be stably achieved by performing the desiliconization treatment of the hot metal under a predetermined condition using a ladle.

Conventionally, it has been qualitatively known that a lower amount of Si in the hot metal is more advantageous for enhancing the dephosphorization efficiency, and therefore, the desiliconization treatment is performed as a part of the hot metal pretreatment. There is. However, in the conventional desiliconization treatment of hot metal, the Si level in the hot metal after desiliconization is usually around 0.2 wt%, and the amount of Si in the hot metal before dephosphorization is such. It has been thought that the effect of reducing the amount of phosphorus is such that the dephosphorization efficiency gradually increases. On the other hand, in the present invention, the content level of Si in the hot metal before dephosphorization treatment is one digit lower than that of the prior art (0.07 wt% or less, preferably 0.05 wt%).
% Or less, and particularly preferably 0.03 wt% or less), it has been found that a dramatically high dephosphorization efficiency can be obtained. Further, by carrying out a highly efficient dephosphorization treatment on the hot metal having a sufficiently reduced Si amount, the hot metal is made to have a normal P content of a crude steel component (so-called steel component standard value,
(Usually 0.02 wt% or less), and in the subsequent decarburization treatment step, substantially no slag material is charged (thus, slag is not constantly discharged),
Further, it has been found that it is possible to further reduce the amount of steelmaking slag generated and improve refining efficiency by substantially performing only decarburization refining.

The present invention has been made on the basis of such findings, and its features are as follows. [1] Ca with respect to the hot metal having a Si content of 0.07 wt% or less
A hot metal refining method comprising adding an O source and an oxygen source, performing dephosphorization treatment under the following condition (a), and then performing decarburization treatment under the following condition (b). (A) In the refining vessel, the hot metal temperature at the start of dephosphorization treatment
1280 ℃ or more, the hot metal temperature at the end of dephosphorization treatment is 1280
~ 1360 ℃, the hot metal required P for crude steel
Perform dephosphorization refining to below the content (standard value of steel composition). (B) The dephosphorized and refined molten pig iron is charged into a converter-type vessel which is another refining vessel, and decarburized and refined substantially without introducing a slag material. [2] The hot metal refining method of the above [1], characterized in that dephosphorization treatment is performed on the hot metal having an Si content of 0.05 wt% or less. [3] The hot metal refining method of the above [1], wherein dephosphorization treatment is performed on the hot metal having a Si content of 0.03 wt% or less. [4] The hot metal refining method according to any one of the above [1] to [3], wherein the hot metal is desiliconized and then dephosphorized.

[0009]

[0010]

[0011]

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be described below together with the reasons for limitation. In FIG. 1, the amount of Si is 0.19 wt%
When dephosphorization treatment was carried out in the converter type container for each of the hot metal of No. 1 and 0.05 wt% (hot metal temperature at the start of dephosphorization treatment: 128
0 ° C or higher, hot metal temperature after dephosphorization treatment: 1280 to 13
The results of investigating the progress of hot metal dephosphorization are shown for 60 ° C. and added on quick lime). Si amount: 0.05 wt
%, In the dephosphorization treatment of the hot metal, the P content in the hot metal reaches the minimum level in less than half the time compared with the case where the hot metal of 0.19 wt% is dephosphorized.
It can be seen that it is lower than that when 0.19 wt% of hot metal is dephosphorized.

Since such test results were obtained,
Further, the effect of the amount of Si in the hot metal subjected to the dephosphorization treatment on the dephosphorization efficiency was investigated. In this test, desiliconization treatment was performed before the dephosphorization treatment to adjust the amount of Si in the hot metal, and in the converter type container, the hot metal temperature at the start of the dephosphorization treatment was the same as in the test of FIG.
1280 ℃ or more, hot metal temperature at the end of dephosphorization treatment: 1280
The dephosphorization treatment was carried out under conditions of ˜1360 ° C. and addition on quick lime.

FIG. 2 shows the results together with the amount of CaO source added. When the amount of Si in the hot metal used for the dephosphorization process is 0.07 wt% or less, the dephosphorization efficiency is increased due to the high basicity of the slag. Phosphorus distribution Lp (= (wt% P) /
[Wt% P], (wt% P): P concentration in the slag, [w
t% P]: P concentration in the hot metal) rapidly increases, and a remarkable improvement in dephosphorization efficiency is recognized. Further, the dephosphorization efficiency increases as the Si content in the hot metal decreases, and the highest dephosphorization efficiency is obtained when the Si content in the hot metal is approximately 0.03 wt% or less.

On the basis of the above results, in the method of the present invention, it was decided to perform the dephosphorization treatment on the hot metal having a Si content of 0.07 wt% or less. Further, from the results of FIG. 2, a more preferable Si amount before the dephosphorization treatment is 0.05 wt% or less, further preferably 0.03 wt% or less. In carrying out the method of the present invention, the amount of Si in the hot metal before the dephosphorization treatment is the above upper limit value (0.
07 wt%, preferably 0.05 wt%, and particularly preferably 0.03 wt%), desiliconization treatment is performed to reduce the amount of Si in the hot metal to the upper limit or less, and then dephosphorization treatment is performed. . Generally, the hot metal discharged from blast furnaces is 0.30
It contains about 0.50 wt% of Si, and in the case of such a normal level of hot metal, it is essential to perform a desiliconization process.

The desiliconization treatment may be carried out by either a hot metal desiliconization process (for example, cast bed desiliconization) or a desiliconization treatment in a container. For desiliconization in a container, a ladle such as a hot metal ladle or a charging pan, a torpedo, etc. are used as the container, and efficient desiliconization can be performed by adding a desiliconizing material into this container and stirring. It can be carried out. As the desiliconizing material, either solid acid (usually iron oxide such as mill scale) or gaseous acid (gaseous oxygen or oxygen-containing gas) may be used, or both may be used together.

The desiliconization treatment carried out in the ladle allows the hot metal to be sufficiently agitated due to the shape of the hot metal holding, and therefore desiliconization is performed more than other hot metal desiliconization processes (for example, a desiliconization process using a cast bed or a torpedo). It is efficient. Therefore, if the amount of Si in the hot metal that has been tapped is relatively high, desiliconize it in the ladle, or cast bed desiliconize and then desiliconize it in the ladle. Preferably. In addition, conventional cast bed desiliconization and the like not only have a low desiliconization efficiency, but also use a solid acid (mill scale or the like) as a desiliconizing material, which causes a problem that the hot metal temperature decreases. On the other hand, in the desiliconization process performed in the ladle, it is possible to supply gaseous oxygen as a desiliconizing material, so it is easy to maintain and stabilize the hot metal temperature, and the solid oxygen source can also be supplied. It is also easy to adjust the hot metal temperature.

The ladle may be a so-called blast furnace ladle that directly receives the hot metal from the blast furnace cast metal through the blast furnace cast bed, or a so-called charging ladle in which the hot metal is transferred from the blast furnace ladle to charge the converter or the like. included. Further, if the pot has a hot metal holding shape similar to that of a blast furnace pot or a charging pot, this can also be used as a ladle. The desiliconization treatment with a ladle may be carried out in at least one of these ladles such as a blast furnace pot and a charging pot.

FIG. 3 shows the relationship between the amount of Si in the hot metal after desiliconization and the desiliconization oxygen efficiency in the case of performing desiliconization in a ladle and cast bed desiliconization. According to the same figure, in the cast bed desiliconization, the desiliconization oxygen efficiency greatly decreases as the Si content in the hot metal after the treatment decreases. Therefore, long-time treatment is required to desiliconize the Si content of 0.07 wt% or less, which is a condition of the present invention, and such desiliconization is not practical in actual operation. On the other hand, desiliconization in a ladle achieves higher desiliconization oxygen efficiency than cast bed desiliconization, and the amount of Si, which is the condition of the present invention, is 0.07 wt% or less (preferably, 0.
It can be seen that it is preferable to carry out desiliconization in a ladle in order to efficiently desiliconize up to 05 wt% or less, more preferably 0.03 wt%.

Further, as mentioned above, since the silicidation treatment in the ladle is usually carried out by supplying gaseous acid, there is no possibility of lowering the hot metal temperature which may affect the handling of the hot metal or the refining of the lower process. It is easy to secure the hot metal temperature and adjust the temperature.Therefore, the hot metal temperature can be adjusted by changing the gas acid supply to the solid acid supply or by using both gas acid supply and solid acid supply as needed. It is easy to stabilize it at a desired level.

Further, in the desiliconization treatment of hot metal, the desiliconization width (Δ% S
When i) becomes large, slag foaming becomes remarkable,
In some cases, it may be virtually impossible to operate. Therefore, when the total desiliconization width is relatively large, slag foaming is performed by performing cast bed desiliconization and then ladle desiliconization to reduce the desiliconization width in one desiliconization process. It is preferable to suppress. Further, by performing the desiliconization treatment in two steps in this way and reducing the desiliconization width in one step, it is advantageous because the slag removal time after the desiliconization in the ladle is particularly short.

As mentioned above, the desiliconization treatment in the ladle is
The major characteristic of this method is that by supplying gas acid as a silicon removal material, the silicon removal efficiency is increased and the drop in hot metal temperature is prevented. It is preferable to use an acid. The gaseous oxygen (gaseous acid) used in the present invention may be either oxygen gas or oxygen-containing gas. The method of supplying this gas acid into the ladle is as follows: (1) spraying the hot metal from above with a top blowing lance, (2) blowing it into the hot metal through an injection lance, and (3) the ladle body. A method of blowing into the hot metal through a blowing nozzle such as a bottom blowing nozzle can be adopted, and vapor acid can be supplied by any one of these or a combination of two or more methods.

Another characteristic of the desiliconization treatment in the ladle is that a sufficient stirring of the hot metal can be obtained, and the stirring of the hot metal can be carried out by using gas acid or other stirring gas (for example, nitrogen gas) in the hot metal. )
It can be realized by blowing. As a specific method, a method of blowing gas into the hot metal through the injection lance described above, a method of blowing gas into the hot metal through a blowing nozzle, or the like can be adopted, and any one of these methods or a combination of two or more methods can be used. It is feasible.

Usually, in the desiliconization treatment in the ladle, the slag-making material and the solid acid as needed are supplied. The methods for supplying these solid additive materials are: 2) The method of spraying the hot metal from above through the top blowing lance, (3) the method of blowing into the hot metal through the injection lance, etc. can be adopted, and the solid additive is supplied by any one of them or a combination of two or more methods. You can
However, as the supply of the solid additive, the method (3) can enhance the stirring force of the hot metal by using the kinetic energy of the solid additive, rather than the methods (1) and (2). Therefore, it is advantageous in increasing the desiliconization efficiency. Usually, a CaO source such as lime powder is supplied as the slag material, and a mill scale, a sintered powder or the like is supplied as the solid acid.

FIG. 4 shows an example of the desiliconization process using a ladle. In this example, gas acid (oxygen gas) is blown through the top blowing lance and slag material (such as lime powder) is injected through the injection lance. Pneumatic gas: N ₂ ) is blown in,
Furthermore, if necessary, solid powder such as sintered powder or mill scale can be placed on the ladle from above. To give an example of the operating conditions for desiliconization with such a ladle,
When performing hot metal desiliconization mainly on the supply of gas acid in a 150 ton blast furnace pan, the amount of gas acid supplied by the top blowing lance: 250
The operating condition is 0 Nm ³ / hr, the amount of lime powder (slag material) supplied by the injection lance: about 200 kg / min.

Further, in order to secure the hot metal temperature at the start of the dephosphorization treatment, which will be described later, it is preferable to adjust the temperature of the hot metal in the desiliconization treatment, if necessary. This temperature adjustment can be performed by appropriately selecting and adding solid acid and gas acid as a desiliconizing agent, but as described above, desiliconizing in the ladle is more advantageous in adjusting the hot metal temperature. be able to.

In the dephosphorization treatment, the Si content is 0.07 wt% or less,
It is preferably 0.05 wt% or less, particularly preferably 0.0
It is performed by adding a CaO source and an oxygen source to the hot metal of 3 wt% or less . Usually, this dephosphorization treatment is performed using a hot metal ladle or a converter type container, but there is no special restriction on the container to be used,
Depending on the case, desiliconization treatment and dephosphorization treatment may be sequentially performed in the same container. In this case, at least a part of the slag is removed after the desiliconization process, and then the dephosphorization process is performed. As the CaO source that is a medium-soluble material, quicklime is usually used, but it is not limited to this. These solvent and solid acid are added into the container by a method such as top-up addition or injection. Further, the gas acid is generally added by a method of blowing oxygen gas into the hot metal and / or spraying it with a lance or a bottom blowing nozzle.

There are no particular restrictions on the method for carrying out the dephosphorization treatment and the processing conditions, but in order to carry out the dephosphorization treatment with particularly high efficiency, it is preferable to carry out the dephosphorization treatment under the following conditions. In particular
In the present invention, the following (1) and (2) are essential conditions
And perform dephosphorization refining. (1) The hot metal temperature at the start of the dephosphorization treatment is 1280 ° C or higher (more preferably 1320 ° C or higher). (2) The hot metal temperature at the end of the dephosphorization treatment is set to 1280 to 1360.
C. (more preferably 1300 to 1340.degree. C.). (3) A CaO source and an oxygen source are supplied to the bath surface in the dephosphorization treatment container or to the same position in the bath. (4) FeO-CaO as a part or all of the solvent medium
Add a system solvent.

First, the condition (1) above will be described. In the method of dephosphorizing low-Si hot metal as in the method of the present invention, the basicity (= CaO / SiO ₂ ) of the slag increases, so the melting point As a result, the initial slag formation of the solvent material becomes insufficient, and the dephosphorization efficiency is likely to decrease. In order to prevent such a decrease in dephosphorization efficiency, the initial slag formation is promoted by setting the hot metal temperature at the start of the dephosphorization treatment to a reference value or higher,
It is effective to generate molten FeO at an early stage. Therefore, the hot metal temperature at the start of the dephosphorization treatment is preferably 1280 ° C or higher, more preferably 1320 ° C or higher.

FIG. 5 shows the relationship between the hot metal temperature at the start of the dephosphorization process and the dephosphorization efficiency (at the end of the dephosphorization process) when the dephosphorization process was performed in a converter type vessel and in the hot metal ladle. Hot metal temperature: 1280 to 1360 ° C, Si in hot metal before dephosphorization treatment
Amount: 0.07 wt% or less, converter type container: quicklime added on top, hot metal ladle: quicklime added + partial injection added), and the hot metal temperature at the start of dephosphorization treatment was 12
It is understood that particularly excellent dephosphorization efficiency (phosphorus distribution Lp) can be obtained by setting the temperature to 80 ° C. or higher, and more preferably 1320 ° C. or higher. Further, according to the figure, compared with the dephosphorization treatment by the hot metal ladle, the dephosphorization treatment by the converter type container has a higher stirring efficiency, so that the treatment time is limited.
It can be seen that higher dephosphorization efficiency is obtained.

Furthermore, it is preferable to set the dephosphorization treatment start temperature to a high value as described above, because iron loss (loss of granular iron suspended in slag) can be reduced. Fig. 6 shows the effect of the hot metal temperature at the start of dephosphorization treatment on iron loss to the slag during dephosphorization refining. Iron loss is remarkable when the hot metal temperature is 1280 ° C or higher, and more preferably 1320 ° C or higher. It can be seen that it has been reduced to. Therefore, also from the above viewpoint, it is desirable that the hot metal temperature at the start of the dephosphorization treatment is 1280 ° C. or higher, preferably 1320 ° C. or higher.

Next, the condition (2) will be explained. The dephosphorization efficiency of the hot metal is better in equilibrium when the hot metal temperature is relatively low, but if the hot metal temperature is too low, slag formation of the medium-melting material occurs. However, the dephosphorization efficiency is rather lowered due to insufficient heating, and therefore the dephosphorization treatment temperature has a proper range in terms of the dephosphorization efficiency because the dephosphorization is performed within the operation upper limit time. This proper temperature range is 1280 at the hot metal temperature at the end of the dephosphorization treatment.
˜1360 ° C., more preferably 1300˜1340 ° C., and good dephosphorization efficiency can be secured by finishing the dephosphorization treatment at this hot metal temperature.

FIG. 7 shows the relationship between the hot metal temperature at the end of the hot water removal process and the hot water removal efficiency when the hot water removal process was performed in a converter-type vessel (hot metal temperature at the start of hot water removal process: 1280 ° C. or higher, The amount of Si in the hot metal before phosphorus treatment: 0.07 wt% or less, added on quick lime), the hot metal temperature at the end of the dephosphorization treatment was 12
80 to 1360 ° C, more preferably 1300 to 1340
By setting the temperature to ℃, especially excellent dephosphorization efficiency (phosphorus distribution L
It can be seen that p) is obtained.

Regarding the above condition (3), Ca
Supplying the O source and the oxygen source to the bath surface in the dephosphorization treatment vessel or at the same position in the bath, that is, F by the supplied oxygen source
By simultaneously supplying the CaO source to the eO generation point, slag formation due to the reaction of CaO + FeO is promoted, and as a result, the dephosphorization efficiency is enhanced.

FIG. 8 shows the results of dephosphorization treatment using a converter type vessel (hot metal temperature after dephosphorization treatment: 1280 to 1360 ° C., Si content in hot metal before dephosphorization treatment: 0.07 wt% or less) When the CaO source and the oxygen source are supplied to the bath surface in the container or to different positions in the bath (quick lime: top addition, gaseous oxygen: top blowing), the CaO source and the oxygen source are added to the bath surface or the bath in the container. When supplied to the same position inside (quick lime + gaseous oxygen:
The relationship between the hot metal temperature at the start of the dephosphorization process and the dephosphorization efficiency is shown. According to the figure, it is better to supply the CaO source and the oxygen source to the bath surface in the container or to the same position in the bath, to supply the CaO source and the oxygen source to the bath surface in the container or to different positions in the bath. It is understood that a relatively excellent dephosphorization efficiency (phosphorus partitioning Lp) can be obtained.

Regarding the above condition (4), FeO-C containing CaO source and oxygen source in a part or all of the medium material.
The CaO source and the oxygen source are supplied to the bath surface in the container or at the same position in the bath by using the aO-based solvent.
The same action and effect as in the case of can be obtained. This FeO-Ca
As the O-based solvent, calcium ferrite, a sintered product of a mixture of calcia and ferrite, or the like can be used.

FIG. 9 shows the results of dephosphorization treatment using a converter-type vessel (hot metal temperature at the end of dephosphorization treatment: 1280 to 1360 ° C., Si content in hot metal before dephosphorization treatment: 0.07 wt% or less) Quick calcium is used as a CaO source (solvent)
When the O source and the oxygen source are supplied to the bath surface in the container or at different positions in the bath (quick lime: top-position addition, gaseous oxygen: top blowing), the FeO-CaO-based solvent (FeO) is used as the solvent.
2 shows the relationship between the hot metal temperature at the start of the dephosphorization treatment and the dephosphorization efficiency in the case of using (a mixed sinter of + CaO) (solvent: top-position addition, gaseous oxygen: top blowing). According to the figure, using the FeO-CaO-based solvent as the solvent is relatively superior to supplying the CaO source and the oxygen source to the bath surface in the container or separate positions in the bath. It can be seen that dephosphorization efficiency (phosphorus distribution Lp) is obtained.

Further, as shown in FIG. 5, the method of the present invention is particularly effective when the dephosphorization treatment is carried out using a converter type vessel. This is because the converter type container has a large freeboard as compared with a ladle and torpedo, so that the stirring power can be increased, which causes rapid slagging and mass transfer of P.

As described above, since the hot metal refining method of the present invention can obtain a high dephosphorization efficiency, even if the P concentration in the blast furnace hot metal becomes high by using a raw material such as iron ore having a high P concentration, Compared with the conventional method, it is possible to reduce the load such as an increase in the processing time and the amount of the medium-soluble material. Therefore, it is possible to flexibly deal with the fluctuation of the hot metal component. In addition, since high dephosphorization efficiency can be obtained as described above, the amount of slag produced at the same dephosphorization amount can be reduced as compared with the conventional method, and this also enables flexible response to changes in hot metal components compared with the conventional method. it can.

Further, when the dephosphorization treatment is carried out using a converter type container, if the entire amount of scrap to be charged into the converter type container is charged before the molten iron is charged into this converter type container. The scrap is easily melted, and the production amount of dephosphorized and refined hot metal can be increased. In the dephosphorization refining in the refining method of the present invention, particularly in the dephosphorization refining in a converter-type vessel, the dephosphorization refining time can be shortened compared to the conventional time, so that before the molten iron is charged into the converter for performing the dephosphorization refining It is possible in time to load the entire amount of scrap to be charged. Further, since the hot metal to be dephosphorized and smelted has a high carbon content, the scrap is easily melted, so that a relatively large amount of scrap can be charged. Further, in the conventional less slag blowing (decarburization) using hot metal dephosphorization pig iron, there was a problem that scrap was hardly melted due to insufficient heat capacity and production elasticity was poor. A normal level of scrap usage can be secured in the treatment process.

When the scrap is charged into the converter type container as described above, the slag generated in the dephosphorization process and / or the decarburization process is used as a part or all of the scrap to be charged. It is possible to use magnetic separation dust, which makes slag generation smooth even when the hot metal temperature is relatively low, and the P content at the dephosphorization refining end point is stably lowered. The magnetic separation dust is a portion containing a large amount of granular iron and the like (usually Fe: about 50 wt%) obtained by selecting slag generated in the dephosphorization treatment step and the decarburization treatment step by a magnetic separator.

By the way, as described above, the dephosphorization refining of the hot metal is performed in a refining vessel such as a ladle or a converter type vessel, and the dephosphorized refining hot metal is transferred to another converter type vessel. In the steelmaking method of refining, the amount of slag generated can be reduced as compared with the conventional method, but as a recent tendency, further reduction of the amount of steelmaking slag is desired. In this respect, for example, Japanese Patent Publication No. 2-14404 described above discloses a technique of reducing the amount of slag generated in the entire steelmaking process by using slag generated in decarburization refining in dephosphorization refining. However, this alone cannot sufficiently meet the recent demand for reducing the amount of steelmaking slag generated.

In decarburization refining, manganese ore is charged to save the use of expensive manganese alloy,
Although it has been partially implemented to reduce this to increase the Mn content in molten steel, the reduction yield of Mn in manganese ore to molten steel is not always sufficient. For example, in the technique disclosed in Japanese Patent Publication No. 2-14404, MnO contained in slag generated in decarburization and refining is discharged outside the system without being effectively used. As a result, MnO in the slag is diluted by newly adding a slag material in decarburization refining, which is one of the factors that reduce the reduction yield of Mn in the charged manganese ore to molten steel. It has become one.

In order to solve such a problem, the hot metal having a sufficiently reduced Si content according to the method of the present invention is subjected to a high-efficiency dephosphorization treatment, so that the hot metal has a P content of an ordinary crude steel component ( So-called steel composition standard value, usually 0.02 wt% or less)
Dephosphorization up to, and in the subsequent decarburization treatment step, substantially without introducing slag material (hence, without constantly discharging slag) and substantially decarburizing and refining. As a result, it was found that the amount of steelmaking slag generated can be further reduced and the refining efficiency can be improved.

Therefore, in the method of the present invention, dephosphorization treatment and decarburization treatment are carried out in the following forms. [1] A refining method in which dephosphorization treatment is performed under the following condition (a), and then decarburization treatment is performed under the following condition (b). (A) According to the method of the present invention, the hot metal is dephosphorized and refined in the first refining vessel to a P content (standard value of steel composition) required for crude steel or less. (B) The dephosphorized and refined molten pig iron is charged into a converter-type vessel which is a second refining vessel, and decarburized and refined substantially without introducing a slag material.

Further, preferred embodiments of the method of the present invention in the case where such a steelmaking method is applied will be shown below. [2] In the refining method of [1] above, in the decarburization treatment step,
The molten steel after decarburization refining is tapped, and only slag corresponding to the amount of slag increased during the decarburization refining is discharged as needed. [3] In the refining method of the above [1] or [2], manganese ore is charged in a converter type vessel for decarburizing and refining, and the Mn content in molten steel at the end of decarburizing and refining is required as crude steel. To be M
Increase within the upper limit of n standard value. [4] In the refining method of the above [3], according to the amount of SiO ₂ contained in the manganese ore charged, a predetermined basicity (Ca
A slag material containing CaO is charged so that O / SiO ₂ ) is secured.

[5] In the refining method according to any one of the above [1] to [4], prior to charging dephosphorized and refined molten iron into a converter type vessel for decarburizing and refining, the converter type Charge the slag solidifying agent into the container. [6] In the refining method of the above [5], light burned dolomite and / or raw dolomite is used as a slag solidifying agent. [7] Charge by the refining method of any of the above [1] to [6] is carried out at a rate of 80% or more in a series of refining operations.

In the above embodiments [1] to [7], in particular, dephosphorization treatment is performed in a converter type vessel, that is, dephosphorization refining and decarburization refining are sequentially performed in different converter type vessels. The most efficient and preferred embodiment in this case is as follows. [8] In the refining method according to any one of the above [1] to [7], a converter type container is used as the first refining container for performing dephosphorization treatment, and the molten iron is charged into the converter type container. First, the entire amount of scrap to be charged into the converter type container is charged.

[9] In the refining method of the above [8], as a part or all of the scrap to be charged, the magnetic separation scrap of the slag produced in the dephosphorization treatment step and / or the decarburization treatment step is used. [10] In the refining method of the above [8] or [9], decarburization refining is performed within the dephosphorization refining time. Hereinafter, the reasons for carrying out the refining methods of the above [1] to [10] and the effects will be described.

Method [1] above: The hot metal is subjected to high-efficiency dephosphorization treatment in accordance with the method of the present invention so that the hot metal has a P content of the crude steel (standard composition of steel). Since it is easily dephosphorized and refined up to the value), it is not necessary to charge a slag material such as burnt lime for refining P in the subsequent decarburization and refining, and the amount of slag can be reduced accordingly. The decarburization refining can be extremely simplified and the refining time can be shortened. Therefore, the steelmaking efficiency can be improved as a whole.

Method [2] above: In decarburization refining, substantially no slag material is charged, but light burned dolomite or the like may be charged prior to hot metal charging to extend the life of the furnace body. Therefore, the amount of slag may increase to some extent. In such a case, the increased amount of in-furnace slag is discharged as needed.

Method [3]: The Mn content of the blast furnace hot metal is usually 0.2 to 0.3 wt%, and the Mn content of the dephosphorized and refined hot metal is usually 0.15 to 0.25 wt%. is there.
Moreover, it is the same in decarburization refining. On the other hand, the Mn content (standard value) of crude steel varies depending on the steel type, but is 0.40 to 0.60 wt% for low carbon steel and 1.0 to 1.2 wt% for high manganese steel. In the conventional refining method, since substantial dephosphorization refining is performed even in the decarburization treatment step, it is necessary to increase the FeO concentration in the slag. Further, since the slag material is also added, the MnO concentration in the slag is diluted. Therefore, a sufficient Mn yield cannot be obtained even when manganese ore is charged in the decarburization treatment step. Therefore, an expensive manganese alloy is added at the time of tapping after dephosphorization refining to make it a standard value.

On the other hand, in the above refining method of the present invention, since it is not necessary to carry out substantial dephosphorization refining in the decarburization treatment step, it is not necessary to increase the FeO concentration in the slag, and substantially Since no new slag-making material is added, the MnO concentration in the slag can be kept high. Therefore, even if manganese ore is charged, it is efficiently reduced and a high Mn yield can be obtained. Therefore, the Mn content in the molten steel is set to the upper limit of the Mn content of the crude steel (M
n standard value), which enables more economical refining operation.

Method [4] above: Normally, manganese ore is 1
Since it contains 0 wt% or less of silica (SiO ₂ ),
When the amount of manganese ore charged is large, the basicity (CaO / SiO ₂ ) of the slag decreases. Therefore, by charging a slag material containing CaO, it is possible to prevent re-phosphorization into the hot metal,
In addition, the melting loss of the furnace body is suppressed. Method of the above [5]: Before loading the dephosphorized refining hot metal into the converter type vessel for decarburization refining, if the slag solidifying agent is loaded into the converter type vessel, It has a function of suppressing the bumping phenomenon of the hot metal when the hot metal is charged, and secures safe operation.

Method [6] above: As the slag solidifying agent,
Brick scraps, calcined lime, light-burnt dolomite, raw dolomite, etc. can be used, and among them, light-burnt dolomite and / or raw dolomite are most preferable from the viewpoint of solubility, economical efficiency, and extension of furnace life.

Method [7] above: The reduction yield of Mn in the hot metal and Mn in the manganese ore greatly changes depending on the number of charges carried out by the refining method of the present invention with respect to the total charge per day. If the number of charges carried out by the refining method is 80% or more of the total number of charges, the Mn yield (total Mn amount charged in the converter (= total Mn amount in slag and Mn amount in manganese ore)) The ratio (%) of the amount of Mn in the molten steel to the steel is about 60% or more, which is preferable. In addition, other charges (charges less than 20% of the total number of charges) may be performed by a normal refining method (refining refining refining and decarburizing refining in the same blowing).

Method [8] above: Prior to charging molten iron into a converter-type container for dephosphorization refining, if the entire amount of scrap to be charged into the converter-type container is charged, scrap is easily removed. The amount of molten and dephosphorized refined hot metal can be increased. In the dephosphorization refining in the refining method of the present invention, particularly in the dephosphorization refining in a converter-type vessel, the dephosphorization refining time can be shortened compared to the conventional time, so that before the molten iron is charged into the converter for performing the dephosphorization refining It is possible in time to load the entire amount of scrap to be charged. In addition, since the hot metal to be dephosphorized and refined has a high carbon content, it easily dissolves scrap,
A relatively large amount of scrap can be charged. In addition, in the conventional less slag blowing (decarburization) using hot metal dephosphorization,
Although there was a problem that scrap was hardly melted due to lack of heat capacity and production elasticity was poor, according to the method of the present invention, it is possible to secure a usual amount of scrap used in the dephosphorization treatment step.

Method [9] above: As a part or all of the scrap to be charged in the dephosphorization refining, the magnetic separation waste obtained by magnetically separating the slag produced in the dephosphorization refining and / or decarburization refining is used. As a result, even when the hot metal temperature is relatively low, the slag is produced smoothly, and the P content at the dephosphorization refining end point is stably lowered. Method of the above [10]: By carrying out decarburization refining within the dephosphorization refining time, the dephosphorized refining hot metal can be decarburized and refined without waiting time, and the steelmaking efficiency can be improved.

Details of the refining methods [1] to [10] described above will be described below based on the preferred embodiments. In the following, a case where dephosphorization refining is performed using a converter type vessel will be described as an example, but dephosphorization refining may be performed in a ladle, topeed or a specially designed refining vessel. Usually, in the dephosphorization refining performed in a converter type container, oxygen is blown from a lance or the like after charging hot metal, and a predetermined amount of calcined lime or the like is charged as a slag material to make CaO, SiO ₂ , FeO. P is removed from the hot metal by forming a slag containing these as the main components. Then, after the dephosphorization and refining of the hot metal is completed, the furnace is detonated and the hot water is tapped into the ladle through the tap hole.

FIG. 10 shows an outline (one example) of the conventional dephosphorization refining of hot metal. In this example, after charging the scrap into the converter type vessel, for example, after charging 340 ton of hot metal,
Furthermore, oxygen blowing is carried out for about 13 minutes while charging burned lime (6 ton / ch), fluorspar (0.6 ton / ch) as a slag material, and raw dolomite as necessary. Then, rinsing is performed for about 3 minutes to separate the hot metal and the slag. After that, wait for about 4 minutes to soothe the slag foaming, and then tap water. In the example shown in the figure, the dephosphorization refining time is about 36 minutes.

FIG. 11 shows an outline (one example) of dephosphorization refining carried out by using the 340 ton converter type container according to the refining method of the present invention. Further, regarding the refining according to the present invention and the above-mentioned conventional example, Table 1 shows the component composition of the hot metal before and after dephosphorization refining and before and after decarburization refining, and Table 2 shows the refining time distribution. As shown in Table 1, in the conventional example, S of hot metal before dephosphorization treatment
While the i content is about 0.3 to 0.5 wt%, the Si content of the hot metal before the dephosphorization treatment is 0.07 wt% or less in the refining according to the present invention.

[0062]

[Table 1]

[0063]

[Table 2]

In the refining according to the present invention, the Si content is 0.
In order to perform dephosphorization refining of hot metal of 07 wt% or less, as shown in Table 1, the amount of slag is less than that of the conventional example (40 to 50 kg / ton) and 10 kg / ton or less. Further, in the refining according to the present invention, despite performing the dephosphorization refining with a higher basicity and a smaller amount of slag than the conventional example,
Standard component value of P is usually required for crude steel: 0.02w
Refined to t% or less. Therefore, in the subsequent decarburization refining, substantial dephosphorization refining need not be performed.

Further, as shown in Table 2, in the refining according to the present invention, since the amount of slag is small, the slag foaming during dephosphorization refining is also small, and therefore the sedation time (4 minutes in the conventional example) is not required, Further, the slag removal time after tapping could be shortened from the conventional 3.1 minutes to 1.0 minutes. For this reason, the dephosphorization refining time can be shortened from the conventional 36 minutes to 29 minutes, which is about the same as the decarburization refining time (29 minutes). On the other hand, if the dephosphorization refining time of the conventional example is 36 minutes, and if the decarburization refining time is the same 29 minutes as above, the converter type vessel for decarburization refining will have a non-operation time of about 7 minutes. Will occur.

In the ordinary dephosphorization refining, P in the hot metal reacts with FeO in the slag and is absorbed in the slag, and P in the hot metal is removed. Therefore, in order to promote such a dephosphorization reaction, it is necessary to increase the FeO concentration in the slag. Therefore, as shown in Fig. 11, charging iron ore or mill scale in the middle stage of dephosphorization blowing. Is preferred. In order to suppress slag foaming, as shown in FIG. 11, an appropriate amount (for example, 0.5 ton / c
Coke of about h) is charged. Further, in the dephosphorization treatment, the basicity of the slag is preferably about 1.5 to 5 in order to make the dephosphorization refining efficient and shorten the refining time.

The dephosphorized and refined molten pig iron is transferred to another converter-type vessel and subsequently decarburized and refined. FIG. 12 shows an outline (one example) of dephosphorization refining performed by using a 300 ton converter type container in the refining method according to the present invention. In the refining method of the present invention, the decarburization treatment step basically aims only at decarburization refining, and therefore it is preferable to increase the amount of oxygen blown.
Moreover, the P content of the hot metal has already reached the standard value (0.02 wt%).
Because of the following, as a general rule, slag materials such as roasted lime, which are often used conventionally, are not charged except for the first charge in a series of operations.

Therefore, in the above decarburization refining, the increase of slag is small. However, in this decarburization refining, since light burned dolomite and the like may be charged for extending the life of the furnace prior to the hot metal charging, the slag amount may increase to some extent. In such a case, in-furnace slag is discharged as needed. As a result, as shown in Table 1, the amount of slag generated in the furnace is about 10 to 30 kg / ton, which is considerably smaller than that of the conventional example (25 to 35 kg / ton). Moreover, since the slag is left in the furnace in principle even after tapping, the amount of slag to be discharged is the conventional example (20 to 30 k).
g / ton), which is a large decrease.

In the decarburization refining in the refining method of the present invention, it is preferable to charge manganese ore in a possible range. As described above, in the conventional refining method, since substantial dephosphorization refining is performed even in the decarburization treatment step, it is necessary to increase the FeO concentration in the slag. Further, since the slag material is also added, the MnO concentration in the slag is diluted. Therefore, a sufficient Mn yield cannot be obtained even when manganese ore is charged in the decarburization treatment step. Therefore, an expensive manganese alloy is added at the time of tapping after dephosphorization refining to make it a standard value.

On the other hand, in the above refining method of the present invention, since it is not necessary to perform substantial dephosphorization refining in the decarburization treatment step, it is not necessary to increase the FeO concentration of the slag, and in addition, it is substantially Since no new slag-making material is added, the MnO concentration in the slag can be kept high. Therefore, manganese ore (for example, Mn: about 50 wt.
%, Fe: about 10 wt% or less, SiO ₂ : about 10 wt%
Even if the following) is charged, it is efficiently reduced and a high Mn yield is obtained. Therefore, the Mn content of molten steel due to the charging of manganese ore is set to the upper limit of the Mn content of crude steel (Mn
It can be increased up to the standard value), and the refining operation can be performed more economically.

The manganese ore is preferably charged as much as possible within a necessary limit in order to minimize the amount of expensive manganese alloy added. As described above, in the refining method of the present invention, the FeO concentration of slag in decarburization refining is low,
Moreover, since the MnO concentration of the slag is kept high even before the blowing, most of the charged manganese ore is reduced and a high Mn yield is obtained.

However, since manganese ore usually contains 10 wt% or less of silica (SiO ₂ ), if the amount of manganese ore charged is large, the basicity (CaO / Si) of the slag is large.
O ₂ ) may decrease. In this case, a slag material containing CaO, such as burnt lime, is charged to prevent rephosphorization of molten steel and to prevent melting damage of the furnace body. Is preferred.

Further, in the decarburization refining in the refining method of the present invention, prior to charging the dephosphorized refining hot metal into the converter type vessel for decarburization refining, the slag is solidified in the converter type vessel. It is preferable to charge the agent. The slag solidifying agent has an action of suppressing the bumping phenomenon of the hot metal when the dephosphorized hot metal is charged, and thus the safety of operation is secured. As the slag solidifying agent, one kind or two or more kinds of brick waste, calcined lime, lightly calcined dolomite, raw dolomite and the like can be used.

Among the above slag solidifying agents, light burned dolomite and fresh dolomite are particularly preferable from the viewpoints of solubility, economy, and extension of furnace life. That is, when light burned dolomite and / or raw dolomite is added as a slag solidifying agent, these are sufficiently dissolved in the slag during decarburization refining, and have the effect of increasing the MgO concentration. Further, since such slag itself contains MgO up to the solubility limit, it has the effect of suppressing the wear of the furnace brick made of magnesia (MgO) brick and extending the furnace life.

Further, in decarburization refining, it is preferable to perform so-called slag coating, in which the furnace body is tilted after the molten steel is tapped and the slag remaining in the furnace is adhered to the brick lining inside the furnace. This slag coating greatly contributes to extending the life of the furnace body, and as a result, the converter type vessel for decarburizing and refining can maintain the same life as the converter type vessel for dephosphorizing and refining.

The maximum amount of slag discharged from the converter type vessel for decarburizing and refining by this slag coating is about 10 kg / ton, and when the amount is small, it is not discharged at all. As already mentioned, the amount of slag generated by dephosphorization refining is also 1
Since it is 0 kg / ton or less, and part of it can be recycled, the amount of slag discharged to the outside per 1 ton of crude steel can be reduced to about 20 kg / ton or less. As described above, the refining vessel for performing dephosphorization refining may be a ladle, a topeed, or a specially designed refining vessel, but the reaction rate is the fastest and the dephosphorization refining is highly efficient. A converter type container is the most preferable in that it can be carried out.

The charge by the refining method of the present invention is
It is particularly desirable to carry out the refining operation in a series of refining operations at a ratio of 80% or more because the Mn yield becomes about 60% or more. That is, the reduction yield of Mn in the manganese ore greatly changes depending on the number of implemented charges of the refining method of the present invention with respect to the total charge per day, and the number of implemented charges of the refining method of the present invention is 80% of the total number of charges. The above ratio is preferable because a Mn yield of about 60% or more can be obtained.

In FIG. 13, the final steel composition is C: 0.03 to.
When manufacturing low carbon steel with 0.06 wt% and Mn: 0.30 to 0.50 wt%, C: about 4 wt%, Mn:
In a series of operations in which decarburization refining was performed using 0.15 to 0.25 wt% dephosphorized hot metal, the refining method of the present invention was carried out for the total number of charges (total number of charges per day: about 40 charges). The relationship between the ratio of the number of charges and the Mn yield is shown. In this decarburization refining, manganese ore was charged at 2.6 to 4.9 kg / ton (hot metal). According to FIG. 13, M increases as the ratio of the number of charges for implementing the refining method of the present invention to the total number of charges per day increases.
It can be seen that the n-yield is improved, and especially when the ratio is 80% or more, the Mn-yield becomes maximum (about 60 to 80%).

Charges for carrying out the refining method of the present invention may be carried out in any manner with respect to the total number of charges. For example, refining according to the present invention is carried out continuously for 5 charges,
Next, a normal refining operation (a dephosphorization refining and a decarburization refining in the same converter type vessel, which is a charging without manganese ore charging) is continuously performed 5 times, and the operation is repeated 4 times a day. Can be adopted.

In the above refining method of the present invention, the refining time in the dephosphorization refining in the converter-type vessel can be shortened as compared with the conventional case. Therefore, before the molten iron is charged in the converter-type vessel in which the dephosphorization refining is performed, the charging is performed. It is possible in time to load the entire amount of scrap to be charged. Further, since the hot metal to be dephosphorized and smelted has a high carbon content, the scrap is easily melted, so that a relatively large amount of scrap can be charged. However, it is preferable that the amount of scrap charged is within about 10 wt% of the amount of hot metal from the viewpoint of heat balance. Scrap charging increases the production of dephosphorized refining hot metal.

Further, as a part or all of the scrap, magnetic separation scraps of slag generated in the dephosphorization process and / or the decarburization process can be used. The magnetic separation dust is a portion containing a large amount of granular iron and the like (usually Fe: about 50 wt%) obtained by selecting slag generated in the dephosphorization treatment step and the decarburization treatment step by a magnetic separator. Since this magnetic separation dust contains about 50 wt% of melted slag, the slag can be produced smoothly even when the hot metal temperature is low, and the P content at the dephosphorization refining end point can be stably reduced.

In the refining method of the present invention, decarburization refining can be performed within the dephosphorization refining time.
Decarburization refining hot metal can perform decarburization refining without waiting time, and can improve steelmaking efficiency. The converter type vessels (converter type vessel for dephosphorization treatment, converter type vessel for decarburization treatment) used in the method of the present invention described above are a top blowing type converter and a bottom blowing type converter. , Top and bottom blowing type converter etc. are included,
In addition to this, a horizontal blowing type converter can also be used.

[0083]

[Examples] [Example 1] Dephosphorization treatment of blast furnace hot metal was carried out using a 300t converter. In this dephosphorization treatment, after the molten iron was charged into the converter, a predetermined amount of slag-making material was added, and oxygen was blown from the top blowing lance. The dephosphorization treatment was carried out in the same treatment time for both the inventive example and the comparative example. In the comparative example, the hot metal that was tapped (Si content: 0.19 wt%) was dephosphorized without being desiliconized, while in the inventive example, the hot metal that was tapped was desiliconized and the Si content was changed. Was set to 0.07 wt% or less, and then dephosphorization treatment was performed. In the desiliconization treatment performed in the example of the present invention, iron oxide (mill scale) was added as a desiliconizing material in the case of cast bed desiliconization, and in the case of pot desiliconization (hot metal ladle), temperature control before and after the treatment was performed. In consideration of the above, gaseous oxygen and solid oxygen (iron oxide) were used together as a desiliconizing material.

Table 3 shows the result, and S in the hot metal is shown.
It can be seen that the example of the present invention, in which the amount of i was reduced to 0.07 wt% or less and the dephosphorization treatment was performed, has a dramatically improved dephosphorization efficiency as compared with the comparative example. Further, in Example 2 of the present invention in which the Si content in the hot metal before the dephosphorization treatment was sufficiently reduced by performing cast bed desiliconization and ladle desiliconization, particularly excellent dephosphorization efficiency was obtained.

[0085]

[Table 3]

[Example 2] Low carbon steel (C: 0.1 wt%)
50%), medium carbon steel (C: 0.1 to 0.2 wt%), and high carbon steel (C: more than 0.2 wt%) were manufactured by 50 charges respectively. Prior to dephosphorization, the hot metal should be degassed from the ladle or cast bed.
Desiliconization was performed by ladle desiliconization to Si: 0.07 wt% or less. Table 4 and Table 5 show the component composition of the hot metal in the manufacturing process.
Shown in. According to Table 4 and Table 5, S of hot metal before dephosphorization treatment
By setting the i content to 0.07 wt% or less, the P content of the crude steel is 0.02 wt% at the end of the dephosphorization treatment.
It is refined below. Further, the Mn content of the crude steel could be increased according to the amount of manganese ore charged.

[0087]

[Table 4]

[0088]

[Table 5]

[0089]

As described above, according to the method of the present invention, the efficiency of the dephosphorization refining performed before the decarburization refining can be dramatically increased as compared with the conventional method, and therefore the processing time of the dephosphorization refining is improved. Can be shortened and the refining cost can be reduced. Further, according to the method of the present invention, the amount of steelmaking slag generated can be further reduced as compared with the conventional method, and the refining treatment can be performed with higher efficiency. Further, since manganese ore can be used as a manganese source in the refining process, extremely economical steelmaking can be realized.

[Brief description of drawings]

FIG. 1 is a graph showing the transition of dephosphorization when hot metal with Si contents of 0.19 wt% and 0.05 wt% is dephosphorized.

FIG. 2 is a graph showing the effect of Si content in hot metal before dephosphorization treatment on dephosphorization efficiency.

FIG. 3 is a graph showing the relationship between the Si content in the hot metal after desiliconization and the desiliconization oxygen efficiency in the desiliconization in a ladle and the cast bed desiliconization.

FIG. 4 is an explanatory diagram showing an example of the implementation status of desiliconization in a ladle.

FIG. 5 is a graph showing the relationship between the hot metal temperature at the start of dephosphorization treatment and the dephosphorization efficiency in the method of the present invention.

FIG. 6 is a graph showing the relationship between the hot metal temperature at the start of the dephosphorization treatment and the iron loss in the dephosphorization refining slag in the method of the present invention.

FIG. 7 is a graph showing the relationship between the hot metal temperature at the end of the dephosphorization treatment and the dephosphorization efficiency in the method of the present invention.

FIG. 8 shows the hot metal temperature at the start of the dephosphorization treatment and the degassing process in the case where the CaO source and the oxygen source are supplied to the same position in the bath surface or different positions in the bath in the method of the present invention. Graph showing the relationship with phosphorus efficiency

FIG. 9 shows a case where quick lime is used as the medium material and the CaO source and the oxygen source are supplied to the bath surface in the container or different positions in the bath, and when CaO source + FeO− as the oxygen source in the method of the present invention. A graph showing the relationship between the hot metal temperature at the start of the dephosphorization treatment and the dephosphorization efficiency in the case of using a CaO-based solvent.

FIG. 10 is an explanatory view showing an example of a dephosphorization refining process in a conventional refining method.

FIG. 11 is an explanatory view showing an example of a dephosphorization refining step in the refining method of the present invention.

FIG. 12 is an explanatory view showing an example of a decarburizing refining process in the refining method of the present invention.

FIG. 13 is a graph showing the relationship between the ratio of the number of charges carried out by the refining method of the present invention to the total number of charges in a series of operations and the Mn yield.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuto Kawashima 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Atsushi Watanabe 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Shigeru Inoue 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (56) Reference JP 5-148525 (JP, A) JP 5-9534 ( JP, A) JP 10-245617 (JP, A) JP 10-168509 (JP, A) JP 10-152714 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21C 1/02 110 C21C 1/04 101

Claims (4)

(57) [Claims] 1. A CaO source and an oxygen source are added to hot metal having a Si content of 0.07 wt% or less to perform dephosphorization treatment under the following condition (a), and then decarburization under the following condition (b). A hot metal refining method characterized by performing a treatment. (A) In the refining vessel, the hot metal temperature at the start of dephosphorization treatment
1280 ℃ or more, the hot metal temperature at the end of dephosphorization treatment is 1280
~ 1360 ℃, the hot metal required P for crude steel
Perform dephosphorization refining to below the content (standard value of steel composition). (B) The dephosphorized and refined molten pig iron is charged into a converter type vessel which is another refining vessel, and decarburized and refined substantially without introducing a slag material. 2. The hot metal refining method according to claim 1, wherein the hot metal having a Si content of 0.05 wt% or less is subjected to dephosphorization treatment. 3. The hot metal refining method according to claim 1, wherein the hot metal having a Si content of 0.03 wt% or less is subjected to dephosphorization treatment. 4. The hot metal refining method according to claim 1, wherein the hot metal is desiliconized and then dephosphorized.