JPS62290815A - Steel making method - Google Patents

Abstract

PURPOSE:To produce low phosphorus steel with high workability and at low cost by using two converter type furnace having both top and bottom blowing functions and executing two step dephosphorizing operations. CONSTITUTION:In two converter type furnaces having top and bottom blowing functions, the one side furnace is used as dephosphorizing furnace 1 and the other side furnace is used as decarburizing furnace 2. Refining agent containing converter slag 4 produced in the decarburizing furnace 2 as main component is added on molten iron 3 poured into the dephosphorizing furnace 1, in which the molten iron 3 is dephosphorized as keeping its temp. to <=1,300 deg.C by top blowing of oxygen gas from lance 6 under executing bottom blow gas stirring by blowing nozzle 5. The dephosphorized molten iron obtained is sent to the decarburizing furnace 2 to execute decarburization and finished dephos phorization.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention (Field of Industrial Application) This invention provides a method for using slag-forming agents (quicklime, etc.) throughout the entire steelmaking process.
The present invention relates to a method for producing high-quality steel at low cost by performing highly efficient dephosphorization while minimizing the amount used.

<Prior art and its problems> In recent years, quality requirements for various steel materials have become more sophisticated day by day, and in line with this, various innovations have been attempted in steel manufacturing methods and various new methods have been introduced.

Under these circumstances, there has recently been great hope for the development of a means to stably melt low-phosphorus steel at even lower costs, and much research is being carried out toward its realization.

By the way, regarding the minimization of the total cost of steel manufacturing and the stable production of low phosphorous steel, the following preliminary dephosphorization method of hot metal has been proposed, and some of it has been put into practical use. Namely, i) a method of performing preliminary dephosphorization by injecting quicklime-based flux or soda ash into the hot metal in the torpedo, ii) a method of injecting or blasting (spraying) quicklime-based flux into the hot metal in the ladle. iii) A method of performing preliminary dephosphorization by blasting quicklime-based flux onto the hot metal in the blast furnace casthouse trough.

However, although relatively low P content levels can be achieved using methods i) and ii) above,
Because dephosphorization relies on the "reaction that progresses during the floating process of the dephosphorizing agent (transitary reactor reaction)," the efficiency of using the dephosphorizing flux is not always good, and the longer the treatment time, the more heat is removed during the treatment. There is a problem that the temperature of the hot metal decreases due to the increase in the temperature of the hot metal.
In method 2, the temperature of hot metal after treatment is higher than in the previous two methods (
However, since the dephosphorization treatment is performed on hot metal immediately after being tapped from the blast furnace, the dephosphorization treatment temperature is approximately 1400℃.
and the reached P content level itself is as high as i) and i
This method has the disadvantage that it is worse than method i), and neither method is satisfactory.

Furthermore, when using quicklime etc. as hot metal dephosphorization flux, considering the amount of quicklime etc. used in the subsequent converter blowing, it is difficult to use any of the above methods. It was also pointed out that the required amount of slag forming agent (amount of quicklime, etc.) was not significantly reduced compared to the method of dephosphorizing using a converter alone.

From the above-mentioned viewpoints, the present inventors have discovered that it is possible to minimize the amount of slag-forming agent used, which greatly affects steel manufacturing costs.
Moreover, in order to provide a method that can produce high-quality steel with high efficiency without requiring particularly new equipment, we first used quicklime, etc., which plays an important role in the melting of high-quality steel with a low phosphorus content. We conducted a basic study on the required amount of slag-forming agent, but
As a result of these studies, ``slag-metal countercurrent refining'', which brings slag and metal into countercurrent contact, determines the amount of slag forming agent required throughout the entire steelmaking process.
However, in practice, it is almost impossible to fully realize countercurrent refining, and currently it is listed as the steelmaking method that is least labor-intensive and has the potential to reduce the amount of slag-forming agent used. What can be obtained is a method in which the dephosphorization process is divided into two stages and the slag generated in the lower process is used as a dephosphorizing agent in the upper process (i.e., a method in which converter slag is used as the main component of flux for hot metal dephosphorization). For example, this method is typified by the "method of reusing converter slag as hot metal dephosphorization flux in outside-furnace refining," which was previously proposed by the present author in Japanese Patent Publication No. 55-30042. I came to strongly recognize that there is.

However, ever? The steelmaking method that reuses ffi-Zed converter slag is extremely difficult to stably secure efficient working conditions because it also uses outside-furnace refining. However, it was not expensive enough to be used as a means of mass production of high-quality steel, and mass production required special exhaust gas dust collectors and dephosphorization slag removal equipment. .

<Means for Solving the Problems> Therefore, the present inventors have fully understood the advantages of the steel manufacturing method by reusing converter slag, and have developed an especially new processing equipment without impairing the advantages. We have conducted various research while searching for a means to efficiently and stably implement the above-mentioned "steel manufacturing method including a two-stage dephosphorization process" that does not require the use of slag and uses a small amount of slag in total. Furthermore, the following matters were re-recognized and newly discovered. In other words, (ill) In the dephosphorization treatment of hot metal, it is better to keep the treatment temperature as low as possible from the viewpoint of dephosphorization efficiency, but if the temperature becomes too low, it will not only cause problems in the next process, but also cause problems in the slag after treatment. Since the problem of increased loss of granular iron occurs, the temperature is best set at about 1,300 to 1,350°C. However, in actual work, the addition of the dephosphorizing agent itself is a major factor in lowering the processing temperature, so it is extremely difficult to maintain the above-mentioned somewhat lower temperature. The processing temperature can be maintained stably and easily.

In order to fully utilize the dephosphorizing ability of the flux and increase the dephosphorization efficiency, it is necessary to adjust the treatment temperature as described above, as well as to lack sufficient stirring to achieve a dephosphorization equilibrium state. However, in order to achieve sufficient and efficient stirring in a short time to efficiently dephosphorize high-temperature hot metal, gas stirring using gas blown from the bottom of the processing vessel is most preferable.

(C) In addition, in order to carry out efficient dephosphorization processing, the processing container must have sufficient freeboard (distance from the scene to the top of the container) for slag forming.

(d) It is preferable to use a basic lining in order to reduce erosion of the processing vessel refractories due to slag and increase dephosphorization work efficiency.

(e) In order to increase the efficiency of dephosphorization in a steelmaking process that includes a two-stage dephosphorization process, the efficiency of removing slag from the processing container cannot be ignored, and it is essential to use a processing container that allows easy removal of slag. thing.

If> In order to mass-produce high-quality steel with good workability, sufficient exhaust gas treatment equipment (U collector) is necessary.

(g) Considering these conditions, a converter-type furnace is ideal as a hot metal dephosphorization treatment vessel, especially a combined blowing converter with a top and bottom blowing function that allows stirring gas to be introduced from the bottom of the furnace. When this is used to carry out the above-mentioned "steel manufacturing method including two-stage dephosphorization process", sufficiently efficient dephosphorization can be achieved even if the amount of slag forming agent used throughout the entire steel manufacturing process is extremely small. Being able to mass-produce high-quality steel with high efficiency.

This invention was made based on the above-mentioned knowledge, etc., and as shown in Figure 1, it uses two converter-type furnaces with both upper and lower blowing functions, and one of them is removed. A phosphorification furnace 1 and a decarburization furnace 2 are used, and a refining agent mainly composed of converter slag 4 generated in the decarburization furnace 2 is added to the hot metal 3 injected into the dephosphorization furnace 1, and a stirring gas is added. After dephosphorizing the hot metal while keeping the temperature of the hot metal 3 in the dephosphorization furnace 1 below 1400°C by blowing oxygen gas upward from the lance 6 while performing bottom-blown gas agitation with the blowing nozzle 5, the resulting dephosphorized By decarburizing phosphorous hot metal and final dephosphorizing it in the decarburizing furnace 2, it is possible to produce steel at a normal phosphorus level or low phosphorus steel with good workability and at low cost with an extremely small amount of slag forming agent. It has the following characteristics.

Here, the reason why the treatment temperature in the dephosphorization furnace is adjusted to 1,400°C or less is that if the hot metal treatment temperature is higher than this, decarburization will proceed, the total Fei in the slag will decrease, and the dephosphorization rate will deteriorate. It is from. However, if the temperature is too low, the loss of granular iron to the slag will increase, so the treatment temperature should be 1200~
The temperature is preferably adjusted to 1400°C, preferably 1250 to 1370°C. The treatment temperature is maintained by blowing oxygen gas from the top blowing lance or by blowing oxygen gas from the bottom tuyere.

In other words, the oxygen gas injection in the dephosphorization furnace is performed to ensure the dephosphorization treatment temperature.

Therefore, the top blowing oxygen lance here may be a normal converter lance, but it may also be a new small flow rate lance for dephosphorization. The amount of oxygen gas used is determined by the hot metal temperature and silicon content before treatment, the temperature of the converter slag, the warmth of the dephosphorization furnace, the target temperature of the hot metal to be treated, etc.
m'/ may be less than or equal to 5 to 1 ON m'/l is usually effective. Incidentally, the amount of decarburization at this time is about 0.5%.

As for the above-mentioned "converter type furnace with both top and bottom blowing functions", the currently used "top and bottom blowing combined blowing converter" is the most preferable. Since it is mild, the furnace itself can be made even smaller, so even if it is newly installed exclusively for dephosphorization, there will not be much impact in terms of cost.

The refining agent (dephosphorization flux) used in the dephosphorization furnace is mainly composed of converter slag generated in the decarburization furnace. It is best to mix it as For example, a blending ratio of converter slag: 40-80% by weight, iron oxide: 20-60% by weight, and fluorite: 20-20% by weight is recommended. Of course, it is not fixed to this, but in order to turn converter slag into slag and turn it into dephosphorization slag with a low melting point, and to increase the oxidizing power of slag so that dephosphorization can proceed easily, it is extremely important to use iron oxide in combination. is important. In addition, quicklime, dolomite, or limestone may be added in addition to the above, or hot metal [! Iln] Manganese ore or ferromanganese ore may be added to improve the quality. In addition, fluorite is commonly used as a solvent, but Ca
Cl2, NazO・SiOz, NagCO3
These may be used alone or in combination with fluorite.

The smaller the particle size of these dephosphorized Fura Nox raw materials other than the converter slag is, the more preferable it is from the viewpoint of slag formation, but there is no problem as long as it is of a generally used size.

The amount of refining agent (dephosphorization flux) used in the dephosphorization furnace is determined by the CP) level of the steel to be melted, but usually 5
0kg/or so is fine.

Now, as the converter slag, which is the main component of the refining agent used in the dephosphorization furnace, the molten slag generated in the decarburization furnace is preferable from the viewpoint of thermoeconomics and slag formation of the dephosphorization flux. (When using a molten substance like this, it is poured into a dephosphorization furnace through a pot lined with a refractory). It may be used after cooling and solidifying the material and crushing it into granules or chunks (in addition,
Also at this time, from a thermal standpoint, the higher the slag temperature, the better.)

Just 1. In this case, in order to improve the slag formation in the dephosphorization furnace, the smaller the particle size, the better; however, since converter slag is naturally highly sludge-forming, even if the particle size is less than 100. It does not cause any particular inconvenience, and it can be used even if it is larger than this.

It should be noted that the timing of the converter slag to be used is preferably that of the previous charge, but it goes without saying that it may also be that which came out of the decarburizing furnace before that or that which was generated in the decarburizing furnace of another factory.

Stirring gases blown in from the bottom of the furnace include Ar, Co□, and Co.
, Nz, 02, air, etc.

The degree of agitation of the bottom gas in the dephosphorization furnace is the same as in normal double blowing combined blowing (0.03 to 0.2 Nm3).
/l), but it is of course possible to increase the amount even more with the aim of improving the dephosphorization rate.

When the dephosphorization treatment is performed under the above conditions, the desired dephosphorization can usually be completed within 20 minutes.

Blowing in a decarburizing furnace is basically the same as blowing ordinary hot metal that has been dephosphorized outside the furnace. In addition to slag-forming agents mainly composed of dolomite and dolomite, manganese ore and ferromanganese ore can also be added. By the way, when implementing the steel manufacturing method according to the present invention, it is preferable to perform a preliminary desulfurization treatment on the applied hot metal if possible. The first reason is that the progress of desulfurization is extremely slow in this steelmaking method, but on the other hand, when hot metal that has not been desulfurized in advance is used, the S content in the converter slag increases, and the This is because there is also concern about increasing the molten ES content in the charge. Note that the preliminary desulfurization may be carried out by any of the commonly used melt FJC desulfurization methods. Furthermore, the lower the Si content of the raw material hot metal used in this method, the better. This is because as the Si content in the hot metal increases, the basicity of the slag in the dephosphorization furnace decreases, the dephosphorization ability decreases, and the total amount of quicklime etc. used increases. This shows the relationship between the "Si content in the raw hot metal" and the "required amount of quicklime" when melting ordinary CP level steel (P content is about 0.012%). This can also be confirmed from Figure 2 (incidentally, the P content in the raw hot metal at this time is 0.1%).
). Therefore, it is a good idea to adjust the Si content of the hot metal to 0.3% or less, preferably 0.2% or less. In addition, if it is desired to raise the temperature of the hot metal after treatment due to the conditions of the decarburization furnace, the Si content of the hot metal should be set to 0.2%.
The degree may be more advantageous and should be determined by the local conditions of the factory.

Next, the main effects obtained by this invention are as follows.
For the sake of explanation, they will be listed separately.

<Effects of the invention> ■ Because it is a "two-stage countercurrent refining" that uses converter slag as hot metal dephosphorization flux, the amount of quicklime used in the entire steelmaking process is significantly reduced compared to conventional methods, making it possible to produce low-phosphorus steel. This makes it possible to perform blowing with a smaller amount of quicklime. In addition, FIG. 3 shows the "P content in steel at the end point of the converter" according to the steelmaking method of the present invention.
This is a graph showing the relationship between the amount of quicklime used and the amount of quicklime used. It is clear from FIG. It is.

■ FeO in the converter slag will be effectively used, improving the recovery rate of granulated iron and metal.

-Finally, when manganese ore or ferromanganese ore is used in a decarburization furnace, about half of these ores are not reduced to Mn and remain in the slag as oxides, but in the method of this invention, the Since the slag is reused as hot metal dephosphorization flux, the residual ore mentioned above can be used effectively, resulting in "(Mn) loss reduction" or "(Mn) increase" in hot metal.
useful for.

■ Since the furnace used is a converter-type furnace, for example, even in the case of a dephosphorization furnace, only the dephosphorized pig iron can be tapped from the tapping port into the ladle, and then the slag in the furnace can be discharged into the slag ladle. , removal of slag is easier than in other dephosphorization methods.

■ Since the furnace used is a converter-type furnace with both upper and lower blowing functions, the hot metal can be strongly stirred and the treatment can be carried out in a short period of time, so the amount of heat removed is small, compared to other dephosphorization treatment methods. It is extremely advantageous in terms of thermoeconomics. In particular, when melting converter slag is used, it becomes more thermoeconomically advantageous due to its sensible heat.

■ The slag generated in the dephosphorization furnace used in the method of this invention has a P2O content of 4 to 10%, so it can be used as fertilizer, and since there is no free lime, it can be used as a roadbed material. Effective use is also possible.

■ Since two furnaces are used, P adhering to the furnace body,
0. There is no concern about poor dephosphorization caused by this.

That is, high P z Os slag is produced in the dephosphorization furnace, and low P 20 slag is produced in the decarburization furnace. Since only slag is attached, no dephosphorization failure occurs in the decarburization furnace.

Moreover, when molten converter slag is used, the molten converter slag is charged into the dephosphorization furnace after the hot metal is charged, so there is no fear that a sudden explosive reaction will occur.

■ Since dephosphorization is performed while stirring the bottom-blown gas, there is no need to finely grind the dephosphorizing agent to near powder form as in the conventional hot metal dephosphorization method (this reduces costs accordingly). It becomes possible.

■ If there is an idle converter, it can be used immediately as a dephosphorization furnace, and there is no need to prepare special equipment.

Furthermore, for example, in the case of a factory that operates 1/2 converter furnaces, one furnace can be used as a dephosphorization furnace, and the present invention can be implemented without capital investment by operating 272 converter furnaces. . If it becomes necessary to construct one of the bricks to extend the lifespan of the bricks, measures are taken to carry out conventional converter blowing using only one converter during this time and to avoid using a free furnace. Very flexible refining is possible.

By the way, depending on the factory, two cups of iron may be poured due to the crane capacity, but in this case, in order to simplify the process, it is recommended to process most of the hot metal in the dephosphorization furnace and perform additional iron in the decarburization furnace. It's a good idea.

Next, the present invention will be specifically explained using examples.

<Example> Example 1 First, the upper part of Table 1 was treated with desulfurization and desiliconization in a torpedo.
160 tons of hot metal with the composition shown in Figure 3 was poured into a double blowing combined blowing converter used as a dephosphorization furnace. 20 kg/l of iron ore crushed to a particle size of 30 yen or less, 16 kg/l of iron ore with a similar particle size, and 4 kg/l of bonseki.
A dephosphorization treatment was carried out for 12 minutes by adding these in a mixed state.

As mentioned above, the dephosphorization furnace and decarburization furnace used were both 160-ton top and bottom double blowing combined blowing converters capable of blowing gas from the bottom of the furnace and stirring. The operating conditions shown in Table 2 were adopted.

The dephosphorized pig iron obtained in this way (the composition is shown in the middle row of Table 1) is once tapped into a pot, and then poured into a decarburized furnace.
10 kg/l of quicklime and 1 fluorite used in normal converter operation
Main blowing was carried out using 1 kg/l as a slag forming agent. At this time, iron ore was added as a coolant at appropriate times so that the end point temperature (blowing end temperature) was 1635°C.

The converter slag generated at this time was 20 kg/l, and a series of operations were repeated in which it was added to the dephosphorization furnace together with iron ore and fluorite as a dephosphorizing agent raw material for the next charge to perform dephosphorization. Ta.

As a result, the amount of quicklime used in the entire steelmaking process was 10kg/
With a small value of t, P in steel as shown in the lower part of Table 1
Molten steel having an amount of 0.013% by weight was obtained.

The amount of quicklime used is approximately 17
It is 4.

Example 2 160 tons of hot metal, which had been desulfurized and desiliconized in a torpedo and had a composition as shown in the upper row of Table 3, was poured into a top and bottom double blowing combined blowing converter used as a dephosphorization furnace, and then , molten converter slag generated in a similar type of decarburization furnace, and after pouring 22 kg/l of the slag into a pot lined with large grains, Iron ore 17kg/
The same process as in Example 1 was carried out by adding L and 4 kg/l of fluorite.
Dephosphorization treatment was performed for 10 minutes under the conditions shown in the table.

Next, the obtained dephosphorized pig iron (component composition is shown in the middle row of Table 3) is tapped into a ladle and then poured into a decarburizing furnace, and 10 kg/10 kg of quicklime used in normal converter operation is poured into a decarburizing furnace. l, Bonseki 1k
Main blowing was carried out using 1 kg/l of dolomite as a slag forming agent. At this time, iron ore was added as a coolant at appropriate times so that the end point temperature (blowing end temperature) was 1640°C.

The converter slag generated at this time was 22 kg/l, and a series of operations were repeated in which it was added to the dephosphorization furnace together with iron ore and fluorite as a dephosphorizing agent raw material for the next charge to perform dephosphorization. Ta.

As a result, the amount of quicklime used in the entire steelmaking process was 10kg/
t, when the amount of dolomite used is as small as 1 kg/l, the amount of P in the steel is 0.011 as shown in the lower part of Table 3.
Molten copper weighing 51 stones was obtained. Further, as can be seen from Table 3, as a result of using the molten converter slag, the temperature after hot metal dephosphorization treatment is also more advantageous than in Example 1.

Example 3 An upper and lower double blowing combined blowing converter using 160 tons of hot metal having the composition shown in the upper row of Table 4, which was desiliconized in the blast furnace casthouse trough and then desulfurized in the torpedo, as a dephosphorization furnace. The same type of iron is poured into the converter slag produced in the decarburization furnace, which is cooled and solidified and crushed into particles with a particle size of 30 μm or less.
20 kg/l of iron ore having a similar particle size and 5 kg of fluorite were added in a mixed state and dephosphorized for 13 minutes under the conditions shown in Table 2 in the same manner as in Example 1.

Next, the obtained dephosphorized pig iron (component composition is shown in the middle row of Table 4) is tapped into a ladle and then poured into a decarburizing furnace, and the amount of quicklime used in normal converter operation is 13 kg/1. and fluorite 1
Main blowing was carried out using kg/l as a slag forming agent. At this time, iron ore was added as a coolant at appropriate times so that the end point temperature (blowing end temperature) was 1630°C.

The converter slag generated at this time was 26 kg/l, and the series of operations of adding it to the dephosphorization furnace together with iron ore and fluorite as a dephosphorizing agent raw material for the next charge and dephosphorizing it was repeated. Ta.

As a result, the amount of quicklime used throughout the entire steelmaking process was 13k.
g8, it was necessary to increase the amount of quicklime by 3 kg/l compared to the case of Example 1, but the steelmaking work could still be completed with a smaller amount of quicklime used than in the conventional method.

Example 4 160 tons of hot metal having the composition shown in the upper row of Table 5, obtained by desulfurizing blast furnace pig iron in a torpedo, was poured into a top and bottom double blowing combined blowing converter used as a dephosphorization furnace, and into this, The converter slag generated in a similar type of decarburization furnace is cooled and solidified to 50*
In the same manner as in Example 1, 36 kg/l of iron ore crushed to a particle size of 0.0 m or less, 30 kg/l of iron ore having a similar particle size, and 2 kg/l of fluorite were added in a mixed state. Dephosphorization treatment was carried out for 15 minutes under the conditions shown below.

Next, the obtained dephosphorized pig iron (component composition is shown in the middle row of Table 5) is tapped into a ladle and then poured into a decarburizing furnace, and 18 kg of quicklime, which is used in normal converter operation, is poured into a decarburizing furnace. Main blowing was carried out using 2 kg/l of fluorite and 2 kg/l of fluorite as a slag forming agent. At this time, iron ore was added as a coolant at appropriate times so that the end point temperature (blowing end temperature) was 1640°C.

The converter slag generated at this time weighed 36 kg, and this was added to the dephosphorization furnace together with iron ore and fluorite as a dephosphorizing agent raw material for the next charge, and a series of operations were repeated to perform dephosphorization. .

The composition of the molten steel obtained as a result is also shown in the lower part of Table 5.

As mentioned above, when hot metal with a high Si content of 0.50% by weight is used, the amount of quicklime used throughout the entire steelmaking process is 18 kg/t, which is 8 kgb compared to the case of Example 1. Although it was necessary to increase the amount of lime used, the steelmaking work was still completed with a value that was sufficiently lower than the 140 kg/l of quicklime required for the conventional method (a method that only performs single slag blowing in a converter).

Example 5 160 tons of hot metal having the composition shown in the upper row of Table 6, which had been desulfurized and desiliconized in a torpedo, was poured into an upper and lower double blowing combined blowing converter used as a dephosphorization furnace, and then , 30 kg/l of molten converter slag generated in a similar type of decarburization furnace was poured into a pot lined with refractory, and then further poured into a pot with a particle size of 30 m or less. Iron ore 23kg/l
and 6 kg/l of fluorite were added and dephosphorization was carried out for 12 minutes under the conditions shown in Table 2 in the same manner as in Example 1.

Next, the obtained dephosphorized pig iron (component composition is shown in the middle row of Table 6) is tapped into a ladle and then poured into a decarburizing furnace, and 15 kg of quicklime, which is used in normal converter operation, is poured into a decarburizing furnace. l, fluorite 2k
Main blowing was carried out using 1 kg/l of dolomite and 1 kg/l of dolomite as a slag forming agent. At this time, iron ore was added as a coolant at appropriate times so that the end point temperature (blowing end temperature) was 1650°C.

The converter slag generated at this time was 30 kg/l, and a series of operations were repeated in which it was added to the dephosphorization furnace together with iron ore and fluorite as a dephosphorizing agent raw material for the next charge to perform dephosphorization. Ta.

The composition of the low phosphorus pig iron obtained as a result is also shown in the lower part of Table 5.

As mentioned above, in this case, extremely high quality low phosphorus steel with a P content of 0.005% by weight at the end of converter blowing is used as in "Example 1" and "Example 2". It was obtained in a short time by using a small amount of quicklime, 15 kg/l, which is 5 kg/l more than in the case of melting ordinary (P) level steel.

Example 6 160 tons of hot metal having the composition shown in the upper row of Table 7, which had been desulfurized and desiliconized in a torpedo, was poured into an upper and lower double blowing combined blowing converter used as a dephosphorization furnace, and into this, The converter slag generated in a similar type of decarburization furnace is cooled and solidified to produce 20ta.
20 kg/l of iron ore crushed to the following particle size, 16 kg/l of iron ore having the same particle size, and 4 kg/l of fluorite were added in a mixed state, and dephosphorization was performed for 12 minutes.

Next, the obtained dephosphorized pig iron (component composition is shown in the middle row of Table 7) is tapped into a ladle and then poured into a decarburizing furnace, and 10 kg/10 kg of quicklime used in normal converter operation is poured into a decarburizing furnace. l, fluorite 1k
In addition to adding 1 kg/l of dolomite as a slag-forming agent, 8 kg/l of ferromanganese ore (total Fe content = 22% by weight, total Mn content: 42% by weight) was added to A blowing session was carried out. At this time, iron ore was added as a coolant at appropriate times so that the end point temperature (blowing end temperature) was 1640°C.

The converter slag generated at this time was 20 kg/l, and a series of operations were repeated in which it was added to the dephosphorization furnace together with iron ore and fluorite as a dephosphorizing agent raw material for the next charge to perform dephosphorization. Ta.

As a result, the amount of quicklime used in the entire steelmaking process was 10kg/
With a small amount of t, P i in the blowing end point steel as shown in the lower row of Table 7: 0.014% by weight can be achieved, and Mni in the blowing end point steel can be reduced to 0.40% by weight. “Example 1
'', and the subsequent use of manganese alloy iron could be saved.

In this case, Mt+O in the converter slag is 12% by weight.
and that of “Example 1” (“1nO: 4.5% by weight
), so CMn ) after dephosphorization treatment was also 0.
．． The amount of Mn in the hot metal was 0.19%, which was higher than that in "Example 1" (Mn content in hot metal: 0.19%).

<Overall Effects> As explained above, according to the present invention, it is possible to manufacture high quality steel with high productivity while keeping the amount of slag forming agent low throughout the steel manufacturing process. This makes it possible to bring about extremely useful effects industrially, such as reducing the manufacturing cost of high-quality steel and paving the way to further expand its fields of use.

[Brief explanation of the drawing]

1st I21 is 1. A schematic diagram showing the outline of the steel manufacturing method according to the present invention, Figure 2, shows the process of melting ordinary CP) content level steel.
Figure 3 shows the relationship between the Si content of hot metal and the amount of quicklime required for treatment.
It is a graph showing the relationship with the usage amount. In the drawings, 1... dephosphorization furnace, 2... decarburization furnace, 3... hot metal, 4... converter slag, 4'... dephosphorization slag whose main component is converter slag, 5... Stirring gas blowing nozzle, 6... Lance.

Claims (4)

[Claims] (1) A steelmaking method in which hot metal is refined by using one of two converter-type furnaces having both upper and lower blowing functions as a dephosphorization furnace and the other as a decarburization furnace, and in which the hot metal is refined into the dephosphorization furnace. A refining agent mainly composed of converter slag generated in the decarburization furnace is added to the injected hot metal, and the hot metal is decarburized while keeping the hot metal temperature below 1400°C by blowing oxygen gas upward while stirring the bottom blowing gas. A steelmaking method comprising the steps of performing phosphorization, and decarburizing the obtained dephosphorized hot metal in a decarburizing furnace and final dephosphorizing. (2) The steelmaking method according to claim 1, wherein the converter slag generated in the decarburization furnace is added in a molten state to the hot metal in the dephosphorization furnace. (3) The steelmaking method according to claim 1, wherein the converter slag generated in the decarburization furnace is once cooled and solidified and then added to the hot metal in the dephosphorization furnace. (4) Claims 1 to 3, wherein the hot metal to be treated has been subjected to preliminary desiliconization treatment to reduce Si to 0.30% by weight or less.
The steel manufacturing method described in any of paragraphs.