WO2017159840A1 - Molten-iron pretreatment method - Google Patents

Abstract

Provided is a molten-iron pretreatment method in which converter slag is recycled as a refining agent for molten-iron pretreatment, the molten-iron pretreatment method being characterized by comprising: a first step in which the converter slag is subjected to particle-size regulation so that the converter slag has particle diameters of 3 mm or larger but smaller than 25 mm and the proportion of converter-slag particles each having a particle diameter of 20 mm or larger but smaller than 25 mm is 10 mass% or higher but less than 15 mass% with respect to the total amount of the converter-slag particles; a second step in which the converter slag obtained by the particle-size regulation is introduced into a molten-iron pretreatment vessel; a third step in which Al₂O₃ is introduced into the molten-iron pretreatment vessel in an amount of 1.0 mass% or larger but less than 10.0 mass% with respect to the converter slag amount which is taken as 100 mass%, either after the first step but before the second step or simultaneously with the second step; and a fourth step in which MnO is introduced into the molten-iron pretreatment vessel in an amount of 0.3 mass% or larger but less than 10.0 mass% with respect to the converter slag amount which is taken as 100 mass%.

Description

Hot metal pretreatment method

The present invention relates to a hot metal preliminary treatment method.
This application claims priority based on Japanese Patent Application No. 2016-053234 for which it applied to Japan on March 17, 2016, and uses the content here.

Conventionally, in a hot metal pretreatment process, a hot metal pretreatment (de-P or de-S) is performed using a refining agent (dephosphorization agent or desulfurization agent) containing CaO as an essential component. Here, since the melting point of CaO is as high as 2625 ° C., conventionally, the method of pulverizing CaO to promote reaction hatching in molten steel, or adding CaF ₂ , Al ₂ O ₃ or MgO to lower the melting point The technique of reducing and promoting reaction of slag and molten iron is widely adopted.

In addition, converter slag generated in the converter refining (de-C) process following the hot metal pretreatment process is a technology for recycling slag generated in the steelmaking process (hot metal pretreatment process-converter refining process-secondary refining process). After cooling, pulverizing and increasing the hatching speed, and then using the technology used as a refining agent in the hot metal pretreatment process (Patent Document 1) and ladle slag generated in the secondary refining process The technique (patent document 2) used as is disclosed.

Among the conventional techniques as described above, the invention of Patent Document 1 was made by paying attention to the fact that the converter slag generated in the converter refining (de-C) process contains a lot of CaO and has a high basicity. The invention is significant in that it can reduce the amount of converter slag discharged by recycling. However, according to the experimental investigation by the present inventors, the converter slag alone has a hatching rate of only about 50%, so it is necessary to additionally use a large amount of quicklime (CaO not derived from converter slag). In the invention of Patent Document 1, there is a problem that the effect of reducing the refining agent cost cannot be expected.

The invention of Patent Document 2 is an invention made by paying attention to the fact that the ladle slag generated in the secondary refining process contains a large amount of Al ₂ O ₃ together with CaO. In the invention of Patent Document 2, although the slag formation promoting effect by Al ₂ O ₃ with an effect of lowering the melting point of the slag can enjoy simultaneously the viscosity of the slag increases. When the viscosity of the slag is high, there is a problem that the slag tends to foam, and the risk of occurrence of slopping that hinders operation due to overflow of the slag from a reaction vessel such as a converter or torpedo car.

Japanese Unexamined Patent Publication No. 4-120209 Japanese Unexamined Patent Publication No. 2006-274349

The present invention has been made in view of the above circumstances, and aims to reduce the amount of slag discharged outside the system, avoid the occurrence of slopping, and reduce the amount of quicklime used as a refining agent. An object is to provide a hot metal preliminary treatment method.

(1) The hot metal preliminary treatment method according to one aspect of the present invention is a hot metal preliminary treatment in which the converter slag obtained when refining the molten iron that has undergone the hot metal preliminary treatment step is recycled as a refining agent for hot metal pretreatment. It is a method, Comprising: The particle size of the said converter slag becomes the range of 3 mm or more and less than 25 mm, and the ratio of the converter slag whose particle size is 20 mm or more and less than 25 mm among the said converter slag is with respect to the whole quantity of the said converter slag. A first step of sizing the converter slag so as to be 10% by mass or more and less than 15% by mass; a second step of charging the converter slag after sizing into a hot metal pretreatment container; Al not less than 1.0% by mass and less than 10.0% by mass with respect to 100% by mass of the converter slag after the first step and before the second step or simultaneously with the second step. the ₂ O ₃ in the molten iron pretreatment vessel A third step of entering; and a fourth step of introducing 0.3% by mass or more and less than 10.0% by mass of MnO to 100% by mass of the converter slag in the hot metal pretreatment container; Have.

According to the hot metal preliminary treatment method having the above configuration, it is possible to reduce the amount of slag discharged from the system, avoid the occurrence of slopping, and reduce the amount of quicklime used as a refining agent.

(2) In the molten iron pretreatment method according to the above (1), wherein the Al ₂ O ₃ is, Al ₂ O ₃ contained molten steel passing through the converter refining step secondary refining slag obtained when the secondary refining It may be.

(3) In the hot metal preliminary treatment method according to the above (1) or (2), further after the first step and before the second step, or simultaneously with the second step, You may have the 5th process of throwing in iron oxide of 1.0 mass% or more and less than 20.0 mass% in conversion of FeO with respect to 100 mass% of converter slag in the said hot metal pretreatment container.

(4) In the hot metal pretreatment method according to any one of (1) to (3), the converter slag is 100% by mass in the hot metal pretreatment container simultaneously with the third step. On the other hand, a sixth step of adding one or more of K ₂ O, Li ₂ O, Na ₂ O, CaF ₂ , MgO, and SrO to 0.3 mass% or more and less than 5.0 mass%, respectively. You may have.

According to the hot metal pretreatment method according to the above aspect of the present invention, hatching of the converter slag can be promoted without increasing the viscosity of the slag in the hot metal pretreatment container. While aiming at reduction, generation | occurrence | production of slopping can be avoided and the usage-amount of quicklime used as a refining agent can be reduced.

It is a flowchart for demonstrating the hot metal preliminary processing method which concerns on this embodiment. It is a graph which shows the influence which the ratio of the converter slag with a particle size of 20 mm or more and less than 25 mm exerts on the hatching rate of the converter slag and the clogging rate of the input hopper among the converter slag. Is a graph showing the relationship between the converter slag apply time reference (0 seconds) and was poured timing of Al ₂ O ₃ (apply time) and converter slag slag formation rates.

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

The converter slag obtained when decarburizing and refining the hot metal that has undergone the hot metal pretreatment process is low in the concentration of P (phosphorus) and contains basic slag required for de-P and de-S (nitrogen). It contains a lot of CaO, which is the main component.

In the hot metal preliminary treatment method according to the present embodiment, as shown in FIG. 1, the hot metal preliminary treatment, converter refining, and secondary refining of the blast furnace hot metal are sequentially performed. In the hot metal pretreatment method according to the present embodiment, the converter slag obtained by the converter refining is recycled as a refining agent in the hot metal pretreatment step, whereby quick lime (converter slag) used as a refining agent in the hot metal pretreatment step. In addition to reducing the amount of non-originating CaO), the amount of converter slag out of the system is reduced.

Here, the melting point of the converter slag is about 1400 ° C., and the lump of the converter slag itself does not melt at the hot metal pretreatment temperature of about 1300 ° C. to 1350 ° C.
In the hot metal preliminary treatment method according to the present embodiment, Al ₂ O ₃ , MnO, FeO, K ₂ O, Li ₂ O, Na ₂ O, CaF ₂ , MgO, and SrO are used as substances that promote the low melting point of the converter slag. Are added together with the converter slag, and the particle size of the converter slag is reduced. As a result, the converter slag can be rapidly melted to improve the hatching rate, and the refining efficiency can be improved, that is, the amount of quick lime additionally used as a refining agent can be reduced and the P removal rate can be improved.

In the hot metal preliminary treatment method according to the present embodiment, the converter slag obtained at the time of converter refining (de-C) is discharged, cooled, and then sieved into fine particles to obtain a particle size (equivalent sphere diameter). ), The ratio of the converter slag having a particle size of 20 mm or more and less than 25 mm in the converter slag is 10% by mass or more and less than 15% by mass with respect to the total amount of the converter slag. (First step).
And in order to recycle the converter slag after sizing as mentioned above as the above-mentioned refining agent, it is put into the hot metal pretreatment container (second step).

By setting the particle size of the converter slag in the range of 3 mm or more and less than 25 mm, the reaction interface area is increased and heat transfer is promoted, so that the converter slag can be rapidly melted.
By making the particle size of the converter slag 3 mm or more, it is possible to suppress part or all of the converter slag introduced by dust collection from dissipating outside the reaction vessel, and to fully contribute to the reaction. it can. Therefore, the amount of quicklime used additionally can be suppressed. By setting the particle size of the converter slag to less than 25 mm, a large specific surface area of the converter slag can be secured, and the melting time of the slag can be shortened, so that the hatching rate increases. Since refining efficiency rises by this, the amount of quicklime used additionally can be controlled.

In addition, among the converter slags that have been sized in the range of 3 mm or more and less than 25 mm as described above, the inventors conducted various tests on actual machine operations with various ratios of those having a particle diameter of 20 mm or more and less than 25 mm. The results shown in FIG. 2 were obtained.

According to the result of FIG. 2, when the ratio of the converter slag having a particle size of 20 mm or more (and less than 25 mm) is 10% by mass or more with respect to the total amount of the converter slag, the ratio of occurrence of clogging of the input hopper is low, There is no significant hindrance to operations. Moreover, when the ratio of the converter slag having a particle size of 20 mm or more (and less than 25 mm) is less than 15% by mass with respect to the total amount of the converter slag, the conversion rate of the converter slag increases.
Therefore, the ratio of the converter slag having a particle size of 20 mm or more (and less than 25 mm) to the total amount of the converter slag is in the range indicated by the arrow in the graph, that is, the grains of the converter slag as described above. By satisfying the diameter condition, the converter slag can be efficiently reused as a refining agent without hindering operation.

In the hot metal pretreatment method according to the present embodiment, Al ₂ O ₃ of 1.0% by mass or more and less than 10.0% by mass is added to 100% by mass (total amount) of the converter slag in the hot metal pretreatment container. Before or simultaneously with the above converter slag injection, that is, after the first step and before the second step, or simultaneously with the second step (third step), 0.3 mass % Or more and less than 10.0% by mass of MnO is added (fourth step). Thereby, hatching of the converter slag can be promoted while avoiding an increase in the viscosity of the slag.

When the addition amount of Al ₂ O ₃ is 1.0 mass% or more, the effect of lowering the melting point of the slag is sufficiently obtained, and the melting point of the slag becomes 1250 ° C. or less, which is the hot metal temperature, and the hatching rate is improved. As a result, the amount of quicklime used additionally can be suppressed.
When the addition amount of Al ₂ O ₃ is less than 10.0% by mass, an increase in slag viscosity is suppressed and foaming of slag is suppressed, so that the probability of occurrence of slopping in which slag overflows from the reaction vessel may be lowered. it can.

When the amount of MnO added is 0.3% by mass or more, an effect of suppressing an increase in slag viscosity can be obtained. As a result, the probability of occurrence of slopping can be reduced.
About the addition amount of MnO, even if it adds exceeding 10.0 mass%, a big change is not seen by the surface of an effect. Therefore, in order to suppress the cost, the amount of MnO added is preferably within 10.0% by mass. As the MnO source, for example, a manganese ore pulverized to about 30 mm can be used. The fourth step of adding MnO may be performed simultaneously with the third step of adding Al ₂ O ₃ , before the third step, or after the third step.

Moreover, the present inventors clarified the relationship of FIG. 3 as a result of the test experiment study. According to the results of FIG. 3, it can be seen that the hatching rate of the converter slag is high when the charging time of Al ₂ O ₃ introduced as the hatching accelerator is before or simultaneously with the converter slag injection ( The range indicated by the arrows in the graph). On the other hand, it was found that when Al ₂ O ₃ was introduced after the converter slag was introduced, the hatching promoting effect was low.

As the Al ₂ O ₃ source, it is preferable to recycle secondary refining slag obtained when secondary refining of molten steel that has undergone a converter refining process. Usually, secondary refining slag contains about 20.0 mass% to 40.0 mass% of Al ₂ O ₃ . Therefore, if the chemical composition of the secondary refining slag is analyzed in advance to determine the input amount, the desired Al ₂ O ₃ concentration can be achieved only by the input of the secondary refining slag.

As described above, the recycling of secondary smelting slag as an Al ₂ O ₃ source reduces the amount of slag generated in the steelmaking process (from the hot metal pretreatment process to the converter refining process to the secondary refining process). It is equivalent and can reduce the cost and environmental burden associated with slag disposal. That is, since the amount of secondary refining slag used matches the amount of emission reduction outside the slag system, the amount of secondary refining slag used can reduce the cost and environmental load associated with slag disposal.
When secondary refining slag is not used as the Al ₂ O ₃ source, Al ₂ O ₃ -containing minerals such as bauxite and gibbsite, waste alumina bricks, and the like can be used.

The above-mentioned FeO is used as a solid oxygen source during hot metal pretreatment. It is preferable to have a fifth step of charging 1.0% by mass or more and less than 20.0% by mass of iron oxide into the hot metal pretreatment vessel with respect to 100% by mass of the above converter slag.
Thereby, the improvement of refining efficiency is realizable. As the iron oxide source, in addition to iron ore, powdered ore sintered into a lump, pellets formed from scale powder and dust, and the like can be used.
The fifth step is preferably after the first step and before the second step, or at the same time as the second step.

The above-mentioned K ₂ O, Li ₂ O, Na ₂ O, CaF ₂ , MgO, and SrO are used as hatching accelerators for reducing the melting point of slag. A first or two or more of these hatching accelerators are added in an amount of 0.3 to less than 5.0% by mass into the hot metal pretreatment vessel with respect to 100% by mass of the above converter slag. It is preferable to have six steps. Thereby, the hatching rate of converter slag can be increased and refinement efficiency can be improved.

When the input amount of the hatching accelerator is 0.3% by mass or more, the refining efficiency is further improved. Moreover, when the input amount of the above hatching accelerator is less than 5.0% by mass, it is possible to suppress the production cost as well as the effect of improving the refining efficiency.

Moreover, the hatching promoting effect of converter slag can be enjoyed by adding these hatching accelerator components at the same timing as Al ₂ O ₃ . As the form when these components are added, in addition to chemical substances purified with the above compounds as main components, compounds containing the above components, for example, K ₂ CO ₃ , Li ₂ CO ₃ , Na ₂ CO ₃ , MgCO ₃ , SrCO Carbonate such as ₃ , ores such as fluorite, feldspar, and dolomite, and those obtained by pulverizing minerals to about 20 mm can be suitably used.

The method for charging the converter slag and the hatching accelerator such as Al ₂ O ₃ , MnO, FeO, K ₂ O, Li ₂ O, Na ₂ O, CaF ₂ , MgO, SrO, etc. is not particularly limited. It may be added to the hot metal pretreatment container at the time of pretreatment.
In addition to an operation mode in which converter refining and hot metal pretreatment are performed in separate smelting vessels, it can be applied to an operation mode in which converter refining and hot metal pretreatment are alternately performed using the same converter.

In the operation mode in which converter refining and hot metal pretreatment are performed alternately using the same converter, after the converter refining treatment, some of the converter slag is left and discharged, and hot metal pretreatment is performed there. It is also possible to perform hot metal pretreatment by introducing hot metal to be performed, and the above-mentioned converter slag fine particles and a hatching accelerator such as Al ₂ O ₃ .

As described above, the hot metal preliminary treatment method according to the present embodiment recycles the converter slag obtained when the hot metal having undergone the hot metal pretreatment process is refined as a refining agent for hot metal pretreatment. It is.
In the hot metal preliminary treatment method according to the present embodiment, the particle size of the converter slag is in a range of 3 mm or more and less than 25 mm, and the ratio of the converter slag having a particle size of 20 mm or more and less than 25 mm among the converter slag is the converter. It has the 1st process of sizing the said converter slag so that it may become 10 to 15 mass% with respect to the whole quantity of slag.
Moreover, the hot metal pretreatment method according to the present embodiment includes a second step of charging the converter slag after sizing into a hot metal pretreatment container.
Further, the hot metal preliminary treatment method according to the present embodiment is based on 100% by mass of the converter slag after the first step and before the second step, or simultaneously with the second step. There is a third step in which Al ₂ O ₃ of 1.0% by mass or more and less than 10.0% by mass is charged into the hot metal pretreatment container.
Further, in the hot metal pretreatment method according to the present embodiment, MnO of 0.3% by mass or more and less than 10.0% by mass with respect to 100% by mass of the converter slag is introduced into the hot metal pretreatment container. It has the process of.
As a result, hatching of the converter slag can be promoted without increasing the viscosity of the slag in the hot metal pretreatment vessel, so that the amount of slag discharged outside the system can be reduced and the occurrence of slopping can be avoided. The amount of quicklime used as a refining agent can be reduced.

[Example]
Below, the result of the experiment example etc. which were implemented in order to confirm the effect of the hot metal preliminary processing method concerning this invention is demonstrated.
First, the converter slag obtained when refining the hot metal that has undergone the hot metal pretreatment process is cooled, and then the finely divided particles are sieved to obtain the converter slag having the particle sizes shown in Table 1 below. Obtained fine granules.

With respect to 100% by mass (total amount) of the granule of the converter slag, Al ₂ O ₃ and MnO in the proportions shown in Table 1 below and other auxiliary materials were charged into the hot metal pretreatment container. And de-P process was performed on the conditions which made other refining conditions the same.
Incidentally, in Table 1, in the experimental examples are described in the column of the value of the "secondary refining slag ratio (wt%)", Al ₂ O ₃ to be turned on, Al ₂ contained in secondary refining slag It is derived from O ₃ .

Table 1 shows the converter slag charging time after Al ₂ O ₃ charging, the de-P ratio (= ([% P] _initial -[% P] _{after completion} ) / [% P] _initial ) according to each experimental example. The ratio of additional quicklime in the decarburization furnace to 100% by mass of the converter slag charged in the hot metal pretreatment, the melting point of the converter slag when Al ₂ O ₃ and MnO, and other auxiliary materials are added to the converter slag, It shows the presence or absence of slopping, the basic unit of reduction of slag emissions by secondary refining slag recycling, the occurrence rate of clogging of secondary material hopper, and the conversion rate of converter slag. The presence or absence of slopping was judged by visually confirming the occurrence of slopping during the hot metal preliminary treatment.

Incidentally, the P removal rate must be 80% or more in order to satisfy the P concentration allowed for the product. The amount of additional quicklime in the decarburization furnace is adjusted in order to achieve a de-P ratio of 80% or more. In the case where the present invention is not carried out, the ratio of additional quicklime is 60 to 90%.
Further, the melting point of the converter slag was about 1400 ° C. when the present invention was not carried out. If the melting point of the converter slag is lowered to the hot metal temperature of 1350 ° C. or less, the hatching rate is improved and the refining efficiency can be improved.

The basic unit for reducing slag out-of-system emissions is essentially the same as the basic unit for secondary slag slag input as an Al ₂ O ₃ source because secondary slag that should be discharged outside the system is recycled. .

When the occurrence rate of clogging of auxiliary material input hopper exceeds 10%, the operation is greatly hindered. Therefore, it is essential that the occurrence rate of clogging of auxiliary material input hopper is less than 10%.
The hatching rate of converter slag is defined as (CaO concentration in slag after refining) / (CaO concentration when all converter slag is dissolved) × 100 (%), which is a value exceeding 40 (%) Then, it was judged that the amount of quicklime used as a refining material could be reduced, so that the refining efficiency could be improved.

As shown in Examples 1 to 30, the ratio of the converter slag having a particle diameter of 3 mm or more and less than 25 mm and the converter slag having a particle diameter of 20 mm or more and less than 25 mm is 10 mass with respect to the total amount of the converter slag. The converter slag that has been sized so as to be not less than 15% and less than 15% by mass is composed of Al ₂ O _{3 of not} less than 1.0% by mass and less than 10.0% by mass, and not less than 0.3% by mass and less than 10.0% by mass. When used together with MnO, it was confirmed that a high P removal rate can be maintained while reducing the amount of quicklime (CaO not derived from converter slag) used compared with Comparative Examples 1-41. Moreover, when secondary refining slag was recycled as the Al ₂ O ₃ source, the amount of slag discharged outside the system could be reduced.

In Comparative Example 1 in which Al ₂ O ₃ was not intentionally added, melting of the converter slag did not proceed, and the P removal rate decreased. As a result of increasing the amount of additional quicklime in order to ensure the P removal rate of 80%, the additional quicklime ratio reached 66% by mass.

Even in Comparative Example 2 in which the maximum particle size of the converter slag is 51 mm, the converter slag is difficult to melt, and in order to secure a P removal rate of 82%, the amount of quick lime (CaO not derived from converter slag) used is 90% by mass. Needed to be increased.

In Comparative Example 3 in which no MnO was added, the viscosity of the slag was greatly increased by Al ₂ O ₃ and the slag was easily foamed, so that the occurrence of slopping was confirmed.

In Comparative Example 4 in which the minimum particle size of the converter slag was 0.8 mm, the converter slag was sucked and lost by the dust collector, so that it could not be sufficiently charged into the hot metal pretreatment furnace, and a large amount was maintained in order to maintain the P removal rate. It was decided to use quicklime.

In Comparative Example 5 in which the input amount of Al ₂ O ₃ was 12.0% by mass, the slag viscosity was remarkably increased and slopping occurred.

In Comparative Example 6 in which the amount of MnO input was 17.0% by mass, both the amount of quicklime used and the P removal rate were good, but since a large amount of manganese ore was used, the cost increased and loss was generated.

In Comparative Examples 30 and 31, in which the ratio of the particle size of 20 mm or more and less than 25 mm is as high as 17% by mass and 50% by mass, respectively, the hatching rate of the converter slag is low, and a large amount of quick lime is necessary to maintain the de-P rate. It was.

In Comparative Example 32 where the amount of Al ₂ O ₃ added was as low as 0.2% by mass, the hatching rate of the converter slag was low, and a large amount of quicklime was required to maintain the de-P rate.

In Comparative Example 33, in which the amount of Al ₂ O ₃ added was as high as 20.0% by mass, significant slopping occurred because the viscosity of the slag increased, and the operation was hindered.

In Comparative Example 34 in which MnO was not added, since there was no effect of lowering the slag viscosity by MnO, slopping occurred and operation was inhibited.

In Comparative Example 35, where the amount of MnO added was as large as 17.0% by mass, both the amount of quicklime used and the P removal rate were good, but because a large amount of manganese ore was used, the cost increased and loss was generated.

In Comparative Examples 36 to 41 in which Al ₂ O ₃ , which is a hatching accelerator, was added 78 to 257 seconds after the converter slag was charged, the hatching rate of the converter slag was a low value of 11 to 25%. To increase the rate, additional quicklime was used in the decarburization process, increasing costs.

In Comparative Examples 7 to 29, in which the ratio of converter slag having a particle size of 20 mm or more and less than 25 mm among converter slags was low, both the amount of quicklime used and the de-P ratio were good, but the ratio of occurrence of auxiliary material hopper clogging The operation was hindered.

As described above, according to the hot metal pretreatment method according to the present invention, hatching of converter slag can be promoted without increasing the viscosity of the slag in the hot metal pretreatment container. Moreover, according to the hot metal pretreatment method according to the present invention, it is possible to avoid an operation hindering factor such as blocking of the charging hopper.

The hot metal preliminary treatment method according to the present invention aims to reduce the out-of-system discharge of slag by reusing slag generated in the steelmaking process as a refining agent, avoiding the occurrence of slopping due to the use of the refining agent, and In the steelmaking process of high-purity steel, the amount of quicklime (CaO not derived from converter slag) used as a refining agent can be reduced, and the value in the industry is extremely high.

Claims (4)

1. A hot metal pretreatment method for recycling converter slag obtained when refining hot metal after the hot metal pretreatment process as a refining agent for hot metal pretreatment,
   The converter slag has a particle size of 3 mm or more and less than 25 mm, and the ratio of converter slag having a particle size of 20 mm or more and less than 25 mm in the converter slag is 10% by mass or more and 15% by mass with respect to the total amount of the converter slag. A first step of sizing the converter slag so as to be less than mass%;
   A second step of charging the converter slag after sizing into a hot metal pretreatment container;
   It is 1.0 mass% or more and less than 10.0 mass% with respect to 100 mass% of the converter slag after the first process and before the second process or simultaneously with the second process. A third step of charging Al ₂ O ₃ into the hot metal pretreatment container;
   A fourth step of charging 0.3% by mass or more and less than 10.0% by mass of MnO to 100% by mass of the converter slag in the hot metal pretreatment container;
   A hot metal pretreatment method characterized by comprising:
2. Said Al ₂ O _3, molten iron pretreatment according to claim 1, characterized in that the Al ₂ O ₃ contained molten steel passing through the converter refining step secondary refining slag obtained when the secondary refining Method.
3. Further, after the first step and before the second step, or simultaneously with the second step, 1.0% by mass or more in terms of FeO with respect to 100% by mass of the converter slag. The hot metal pretreatment method according to claim 1, further comprising a fifth step of charging less than 0% by mass of iron oxide into the hot metal pretreatment container.
4. Further, at the same time as the third step, one kind of K ₂ O, Li ₂ O, Na ₂ O, MgO, CaF ₂ , and SrO with respect to 100% by mass of the converter slag in the hot metal pretreatment container. Alternatively, the hot metal preliminary treatment method according to any one of claims 1 to 3, further comprising a sixth step of adding at least two kinds of them in an amount of 0.3 mass% or more and less than 5.0 mass%.

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