JP2002371311A - Method for dephosphorizing molten metal, dephosphorizing agent with low-temperature slag forming property therefor, and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a slag forming environment suitable for realizing a slag forming synergistic action, when using calcium-ferrite suitable for dephosphoriz ing and quicklime together. SOLUTION: This method for dephosphorizing the molten metal is characterized by charging calcium-ferrite CaO-Fe2 O3 into the molten metal, simultaneously with or slightly earlier than charging quicklime CaO, of which the charging amount is equal to or less than that of the calcium-ferrite. Then, the calcium- ferrite 6 melts earlier than the quicklime 5, forms a low-temperature region in the molten metal under an oxidizing atmosphere, and accelerates dephosphorization. The calcium-ferrite preferably includes quicklime of 25-40 wt.%, iron oxide of 50-70 wt.%, and alumina of 2-10 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dephosphorizing molten metal, a low-temperature slag-forming dephosphorizing agent used therefor, and a method for producing the same. More specifically, the present invention relates to a method for dephosphorizing hot metal or molten steel using calcium ferrite. The present invention relates to a slag-making method. Further, the present invention relates to a calcium ferrite composition suitable for the slagging method and a method for producing the same.

[0002]

2. Description of the Related Art It has been well known that a lime-based flux is used to generate desulfurized slag or dephosphorized slag by reacting with sulfur or phosphoric acid contained in a molten metal in a metal refining furnace. ing. A typical example of the flux is quicklime CaO. This is because when silicon contained in the molten metal is oxidized to SiO ₂ ,

(Equation 1) And the phosphorus is

(Equation 2) Gives P ₂ O ₅ ,

(Equation 3) This is because the reaction of

[0003] In addition, the sulfur content causes the following reaction. Note that C is carbon in the molten metal, and the second equation is a case where metallic Mg is also added as a desulfurizing agent.

(Equation 4) However, quick lime includes mill scale Fe ₂ O ₃ and fluorite Ca.
In many cases, F ₂ is mixed to improve the slag property.

[0004] Mill scale is an oxidizing agent for promoting dephosphorization, and fluorite functions as a flux for increasing the reactivity of quicklime having a high melting point. That is, the fluorite improves the fluidity of the slag without lowering the basicity of the basic slag, and activates the slag-making action. By the way, dephosphorization and dechromization require a low-temperature and oxidizing atmosphere, but also require that the slag has a high basicity.

[0005] Specifically, mill scale and fluorite are added only in appropriate amounts, but quick lime is usually used in an amount of 30 to 35 kg per ton of molten metal. In the process of removing inclusions with such a slagging agent, a desiliconizing agent, which is a solid oxide such as mill scale, sinter or iron sand, is first supplied to a blast furnace casting bed such as a hot metal gutter or a tilting gutter of a blast furnace. In many cases, CaO or Mg is charged in a topped car or ladle to desulfurize, and then dephosphorized and decarburized in a converter.

[0006] When 30 to 35 kg / ton of quicklime is used as described above, the dephosphorization rate may be as low as 85% even if 5 minutes are desorbed for dephosphorization and 30 minutes are deallocated. Furthermore, when dephosphorizing with a topped car, the temperature of the molten metal may be raised for desulfurization, and part of the dephosphorized material may be dephosphorized, and the dephosphorization rate tends to decrease to nearly 60%.

The desulfurization reaction is also required to have a high basicity. However, contrary to dephosphorization, the desulfurization reaction takes place in a high-temperature reducing atmosphere. (Smelt) migrates in the form of CaS. On the other hand, phosphorus in molten steel is oxidized by gaseous oxygen and oxygen in iron oxide to form P ₂ O.
_{As described above} , it reacts with molten lime to form nCaO · P ₂ O ₅ , but in this form, it migrates into the slag and is fixed. For this reason, it is well known that iron ore containing a large amount of phosphorus has been refined in an acidic Thomas converter or the like, and its slag has been widely used as Thomas phosphorus fertilizer.

However, with the development of basic furnaces, P ₂
Gaseous oxygen, mill scale, and the like have come to be used as an oxygen source required for generation of O ₅ . Therefore, many studies on dephosphorization using calcium ferrite have been made. For example, Japanese Patent Publication No. 39-25884 discloses mud and limestone Ca obtained by adding water to iron oxide dust.
It is described that CO ₃ is mixed and calcined at 1,200 ° C. or more to thereby form calcium ferrite on the surface of quicklime CaO.

When this quick lime coated with calcium ferrite is added to the molten metal as a slagging agent, slagging is rapidly progressing at the end of blowing, but begins to form slag from an early stage, thereby improving the refining efficiency. You. Thus, dephosphorization
The desulfurization effect increases because calcium ferrite having a low melting point promotes the melting of quicklime produced by calcining limestone CaCO ₃ .

Japanese Patent Publication No. 49-48369 also discloses that calcium ferrite is used to improve slagging ability. This calcium ferrite is also coated on quicklime,
It is described that when ferrite 2CaO.Fe ₂ O ₃ is used as a main component, the digestion resistance is excellent, the surface layer has a low melting point, and the slagging speed is increased.

[0011]

By the way, as mentioned at the outset, when using a mixture of mill scale or the like as an oxidizing agent, quick lime as a slagging agent, and fluorite as a solvent,
In order to promote dephosphorization, the temperature must be between 1,300 ° C. and 1,4
At relatively low temperatures, such as 70 ° C., the dephosphorizing agent must be rapidly slagmed to form a highly basic slag. Therefore, it is necessary to determine the composition of the dephosphorizing agent so that its melting point is 1,300 ° C. or less.
However, if the mixture is merely a mixture, only quicklime having a high melting point and an oxidizing agent are unevenly distributed, and the formation of slag is delayed during the dephosphorization treatment, which delays the dephosphorization reaction.

[0012] Based on such a background,
No. 217,513 proposes to use a sintered ore having a low melting point calcium ferrite composition for dephosphorization. In using this slagging agent, in order to sufficiently perform dephosphorization, S in the molten metal before the dephosphorization treatment is used.
The i content is reduced to 0.20% or less. This is because, when the content exceeds 0.20%, desiliconization proceeds together with the dephosphorization reaction, and the yield of the dephosphorizing agent deteriorates.

However, the sintered ore having the composition of calcium ferrite contains not only CaO and Fe ₂ O ₃ but also a manganese content of 20% by weight or less, a fluorine content of 16% by weight or less, and a chlorine content in some cases. It is attempted to lower the melting point of the slagging agent by using such a composition as containing 21% by weight or less.

That is, if fluorite is added, even if 2CaO.SiO ₂ when desiliconized covers the surface of lime, the remaining quicklime can be melted at the furnace temperature to make it easier to react. Standing on the idea. However, the melting point is 2,570
Since fluorite, which weakens the binding of quicklime and promotes melting by as much as ℃, contains fluorine, which is environmentally problematic, dephosphorized slag produced using fluorite is not suitable as phosphorus fertilizer, and As a result, the process is interrupted.

Although dephosphorization using calcium ferrite has already been performed as can be understood from the above description, in any case, slag which has been made to have integrity by coating quicklime or the like. It is an agent. Therefore, P ₂ O ₅ can be generated by calcium ferrite and its slag can be formed. However, since iron oxide in calcium ferrite has been consumed when dephosphorization is completed, the temperature of the molten metal is reduced. When the ascent rises and the decarburization period starts, a situation occurs in which part of the phosphorus fixed on the bent slag returns to the molten metal.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object the most suitable use of calcium ferrite suitable for dephosphorization, while realizing a cooperative slagging action between the slag-making agents. An object of the present invention is to propose a dephosphorization method which can create a slagging environment and suppress rephosphorization during the decarburization stage as much as possible. In addition, the present invention provides a low-temperature slag-forming dephosphorizing agent that can promote the melting of quicklime without adding fluorite, and is itself a calcium ferrite that exhibits a high dephosphorizing action. Law is also to be presented.

In the present invention, when calcium ferrite and quick lime are mixed in a molten metal in an oxidizing atmosphere, phosphorus in the molten metal is reduced to calcium and calcium in a low temperature region generated around the calcium ferrite which melts early. It was completed after obtaining the knowledge that it actively reacts with ferrite.

[0018]

The present invention is applied to a slagging method using a lime-based flux which promotes slag formation by reacting with phosphoric acid contained in a molten metal in a metal refining furnace.
The feature is that, with reference to FIG. 1 (a), calcium ferrite 6 is introduced into a molten metal 7 to be dephosphorized and decarburized, and finally a base of 3.5 to 4.5 is added. That is, the amount of quick lime 5 for generating a slag with a certain degree is introduced.

As shown in FIG. 2 (a), when dephosphorized slag 12 is discharged after dephosphorization and then decarburized, quick lime 10 is added during the decarburization period to remove decarburized slag 11. Generate
The molten decarburized slag is brought into contact with the molten metal 7 to be dephosphorized, and at the same time, calcium ferrite 6 is added.

As shown in FIG. 3 (a), when dephosphorizing and then removing the dephosphorized slag 12 and then decarburizing, the decalcified slag 11 is added by adding quicklime 10 during the decarburizing period. Generate
Iron oxide 14 is added to the molten decarburized slag, and the iron oxide-added molten decarburized slag 11A is brought into contact with the molten metal 7 to be dephosphorized.

The invention of a low-temperature slagging agent used for dephosphorization of molten metal is mainly composed of 25 to 40% by weight of quicklime and 50% of iron oxide.
To 70% by weight and 2 to 10% by weight of alumina.

Quicklime 25-40% by weight, iron oxide 50
Lime, iron oxide, and alumina are introduced into a reverberatory furnace or electric furnace and melted so as to have a composition of about 70% by weight and 2 to 10% by weight of alumina. It is to crush very much. In this case, it is possible to use dense limestone which has crystal grains of 10 μm or more, has a small thermal expansion absorption capacity, and powders when heated.

Further, lime, iron oxide, and alumina, which have been ground in advance, are mixed and granulated so as to have the above-described composition, and the granulated material is charged into a cupola and melted. The ferrite may be crushed to a size of 5 to 30 mm to produce a low-temperature slag-forming dephosphorizing agent.

[0024]

According to the present invention, calcium ferrite is introduced into the molten metal almost at the same time as quick lime, so that calcium ferrite having a lower melting point than quick lime melts first and thus is formed in a low temperature range. The reaction between calcium ferrite and phosphorus in the molten metal proceeds at a stretch. Thereafter, melting of the quicklime is promoted by the molten calcium ferrite, and the phosphoric acid is fixed as slag by the quicklime.

The molten metal with reduced phosphorus is subsequently decarburized. Care is taken that some calcium ferrite remains even during the decarburization period, and the dephosphorizing action on the residual phosphorus in the molten metal is also maintained. Quick lime is added or added in advance so that the basicity of the final slag in the decarburization period is 3.5 to 4.5, so that even if the temperature of the molten metal increases after dephosphorization, rephosphorization in the decarburization period is possible. Can be suppressed.

When the dephosphorized slag is discharged and then decarburized, the decarburized slag in the molten state produced by the decarburization is brought into contact with the molten metal to be dephosphorized, and at that time calcium is removed. -Since ferrite is introduced, calcium ferrite is melted between the decarburized slags to generate a low-temperature melting zone, where the reaction between calcium ferrite and phosphorus in the molten metal can proceed at a stretch.

Thereafter, the production of dephosphorized slag proceeds also by quicklime remaining in the molten decarburized slag. Since the dephosphorized slag is discharged before decarburization, it can be used as phosphorus fertilizer or the like. Since the decarburized slag can be used for dephosphorization, the amount of waste can be reduced.

In the decarburization period, quick lime is added to generate decarburized slag, iron oxide is added to the molten decarburized slag, and the iron oxide-added molten decarburized slag is brought into contact with the molten metal to be dephosphorized. For example, the generation of P ₂ O ₅ is promoted by the iron oxide, and is fixed to the slag by the molten CaO.

25-40% by weight of CaO, Fe ₂ O ₃
50 to 70% by weight, Al ₂ O ₃ 2 to 10% by weight
Calcium ferrite composed of
Its melting point can be kept as low as possible. Furthermore, since Al ₂ O ₃ is contained, a ternary system can be obtained, and the melting point can be further lowered. Such calcium ferrite not only exerts a dephosphorizing action, but also promotes the melting of quick lime to enhance its slagging action.

Calcium ferrite to be subjected to dephosphorization can be produced by melting limestone, iron oxide and alumina in a reverberatory furnace or electric furnace, and since it is in a solid solution, when brought into contact with the molten metal, the molten metal becomes 1,300. Or 1,400
It melts quickly even at a low temperature such as ° C., and dephosphorization proceeds rapidly. Crystal particles of 10 μm as lime
If the above-mentioned dense limestone is used, pulverization proceeds at the time of heating in a reverberatory furnace or the like, dissolution with iron oxide or alumina is promoted, and high quality calcium ferrite can be easily obtained. In addition, limestone, which has little use in limestone, can use limestone, which is still abundant and has a small thermal expansion absorption capacity, and can obtain raw materials at low cost.

The lime, iron oxide, and alumina, which have been pulverized in advance, are mixed and granulated, and the granulated material is melted by cupola to obtain solid solution calcium ferrite. Accompanying lime is suppressed as much as possible, and the formation of calcium ferrite is promoted efficiently. Since the generated calcium ferrite is a solid solution, the dephosphorizing action is not inferior to the production method using a reverberatory furnace or the like.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for dephosphorizing molten metal, a low-temperature slag-forming dephosphorizing agent used in the method and a method for producing the same according to the present invention will be described in detail with reference to embodiments. This is intended to provide a lime-based flux which reacts with a phosphoric acid component or the like contained in a molten metal in a metal smelting furnace to promote the production of molten slag, and to improve the slagging method using the flux.

Briefly, the present invention relates to a calcium ferrite Calcium-F suitable as a dephosphorizing agent.
Errite is used in combination with quicklime to create the most suitable slagging environment to promote the synergistic synergistic action of calcium ferrite and quicklime. In addition, it is intended to promote the melting of quicklime without adding fluorite to promote the activity of slag-making action, and to secure the use of dephosphorized slag as a fertilizer.

First, the main structure of the dephosphorization method of the present invention will be described. That is, a slagging method in which calcium ferrite is charged into molten metal at the same time as or slightly earlier with quicklime CaO. During the slagification, calcium ferrite is added in the same amount or slightly more than quick lime, and the basicity of the final slag after decarburization (CaO / SiO ₂ )
Is set to be 3.5 to 4.5.

The invention of the low-temperature slag-forming dephosphorizing agent is mainly composed of quicklime CaO 25 to 40% by weight, iron oxide Fe
₂ O ₃ 50 to 70 wt%, to alumina Al ₂ O ₃ 2 not is that the calcium-ferrite is 10% by weight, a melting point of for example 1,300 ° C. is suppressed below by giving this composition ratio, the Improving the slag property is also achieved.

The present inventors have found that where calcium ferrite comes into direct contact with molten metal, such as hot metal or molten steel,
It was found that phosphorus reacts with calcium ferrite in the low temperature region around calcium ferrite which melts earlier than quicklime. Although the present invention has been completed on the basis of such findings, specifically, if the dephosphorization reaction of calcium ferrite due to iron oxide rapidly proceeds at a low temperature in an oxidizing atmosphere, this becomes an overall phenomenon. With the spread, dephosphorization will be actively developed.

As an example of the refining to which the present invention is applied, the one shown in FIG. this is,
The pig iron 2 melted in the blast furnace 1 is transferred to the torpedo car 3 without desiliconization, desulfurized in the tope car, dephosphorized in the converter 4 and decarburized in the same furnace body. ing. By doing so, in addition to reducing the total amount of slag generated, the molten metal that has not been desiliconized causes an exothermic reaction of Si + O ₂ → SiO _{2 in} the converter 4 to prevent a decrease in the temperature of the molten metal.

The dephosphorization reaction proceeds as follows.
The underscore in the formula means that it is in the molten metal.

(Equation 5)

As can be seen, P reacts with O to form P ₂ O ₅ , which combines with quicklime to form the more stable compound nCaO.P ₂ O _5, which is fixed in the slag. As described above, since the dephosphorization is performed by generating P ₂ O ₅ , it is necessary to have an oxidizing atmosphere.
If the temperature of the molten metal is high, phosphorus is restored, so that the temperature is preferably low. If there is quick lime having high activity, nCaO.P ₂ O ₅ is easily generated as described above.

Conventionally, calcium lime was coated on the surface of quicklime to form quicklime.
In the present invention, quicklime 5 and calcium ferrite 6
It is separate from. In addition, the composition of calcium ferrite is mainly CaO, Fe ₂ O ₃ , Al ₂ O _3, and the composition ratio is as described above, but is most preferably about 27%, 68%, and 5%, respectively. .

Incidentally, considering the binary system of CaO—Fe ₂ O ₃ ,
20-25% CaO, 80-7 Fe ₂ O ₃
If it is 5%, the solid solution having the lowest melting point of 1,200 to 1,300 ° C. can be obtained even though CaO alone has a melting point of 2,570 ° C. Considering that the desiliconization (Si → SiO ₂ ) reaction precedes at the beginning of the dephosphorization, it is preferable to increase the ratio of iron oxide Fe ₂ O ₃ , and complete the desiliconization and dephosphorization immediately. Will be able to

However, when this calcium ferrite was composed, alumina Al ₂ O ₃ was used as described above.
, The melting of quicklime is promoted in the same way as when fluorite is added, and the slag after dephosphorization is stable,
Thereafter, high-temperature decarburization / cleaning operation of the molten metal with reduced phosphorus can be further facilitated. If fluorite is not used, there is no environmental problem in using dephosphorized slag.

Of course, alumina is different from fluorite in
No base slag base
The slag fluidity is improved without lowering
There is no major obstacle. In addition, Al_TwoO_Threeof
By the addition, CaO-Fe _TwoO_Three-Al_TwoO_ThreeThree yuan
By becoming a system, its melting point tends to be even lower
Become. When desiliconized, 2CaO.SiO is added to the surface of quicklime._TwoBut
It can melt the remaining quicklime at steelmaking temperatures
Al is difficult_TwoO_ThreeMakes it easier to melt
Therefore Al_TwoO_ThreeIs indispensable.

As described above, calcium ferrite
If it is mixed with quicklime, low melting point calcium
・ Ferrite melts out and above the temperature of the molten metal
As a result, the oxygen content in the ferrite is obtained to oxidize phosphorus.
Progresses rapidly. The resulting P _TwoO_FiveIs melted and activated
Combined with CaO, CaO · P_TwoO_FiveSlug in the form
Be transformed into When dephosphorization is almost complete, the molten metal is transferred to another converter.
Needless to say, you can immediately start the decarburization process,
Decarburized slag can be generated by CaO.

The quicklime and calcium ferrite are introduced into the converter almost at the same time. In the present invention, CaO that is difficult to melt is present, so CaO is blown by oxygen blowing.
Even if the temperature of the molten metal that comes into contact with the metal rises, the rise in the temperature of the molten metal is suppressed at the place where the calcium ferrite is melted, so that a low-temperature portion is formed, and conditions suitable for dephosphorization are prepared in that portion. Iron oxide F of molten calcium ferrite
eO, Fe ₂ O ₃ reacts rapidly with phosphorus, which spreads throughout and promotes the production of P ₂ O ₅ .

As can be seen, the dephosphorizing action of calcium ferrite appears remarkably only after the presence of quicklime, while the presence of calcium ferrite makes Ca
The melting of O is promoted, and the generated P ₂ O ₅ is reacted with the melted lime to promote dephosphorization slag formation. As described above, since calcium ferrite and quick lime work together to promote the other action, a high dephosphorization rate can be obtained as a synergistic effect.

By the way, calcium ferrite can be produced according to the procedure described in the section of the prior art, but they are all fired or sintered products. In order to promote the melting of calcium ferrite to enhance the slagging reactivity, it is preferably a solid solution. For that purpose,
The following are three methods.

First, the processing in a reverberatory furnace or electric furnace will be described. As described above, limestone, iron oxide and alumina are placed in a well-known reverberatory furnace (not shown) so as to have a composition of quicklime 25 to 40% by weight, iron oxide 50 to 70% by weight, and alumina 2 to 10% by weight. Add and melt.
The limestone is crushed to a size of 5 to 30 mm and then charged. After complete melting, the furnace body is tilted, and the molten calcium ferrite is flowed through a gutter or the like, and the solid solution calcium ferrite obtained by natural cooling may be crushed by a crusher or the like to a size of 5 to 30 mm.

Such a solid solution operation can be performed not only in a reverberatory furnace but also in an electric furnace. In a reverberatory furnace, heating is carried out by conduction heat of a flame and radiant heat from a furnace lid or the like, and in an electric furnace, heating can be carried out by arc heat or electric resistance heat. In any case, since there is no factor to disperse the charge in the furnace, the raw materials of lime, iron oxide, and alumina can be charged with almost no pretreatment, and handling during production is simplified. .

It should be noted that if the limestone is heated to melt,
It becomes quicklime at around 0 ° C. Therefore, although quick lime may be prepared as a raw material, it is based on the idea that crushed limestone can be used as it is without using it. Of course, in order to obtain a desired composition ratio, at least 100/56 = 1.8 times the required amount of quicklime should be used in consideration of the molecular weight.

By the way, limestone is consumed in a large amount not only in the field of refining such as iron making as in the present invention but also in a cement manufacturing plant. Although limestone is abundant in Japan, only raw materials suitable for the processing steps in each industrial field are used. That is, since there is a step of firing in a kiln, any raw material to be powdered is scattered during firing and taken away by the hot gas flowing in the furnace, and firing cannot be performed.

It is known that powdering of limestone frequently occurs when the crystal particle size is 10 μm or more. This is because the denser the crystal grains, the larger the crystal grains. Dense means that if it is forced to expand due to heat, the gap that can absorb the expansion is small. If the expansion absorption power is small, a large thermal stress is generated and the powder is scattered apart.

However, in the case of melting treatment as described above, pulverization does not pose a problem, but rather powders easily mix with iron oxide or alumina and increase reactivity. Therefore, crystal particles that have not been observed until now have a size of 10 μm.
m or more dense limestone can be used. At present, resources are being depleted even in abundant limestone, and if left untreated limestone can be used, the fear of depletion will be lessened, and it can be said that it is very convenient because it can be obtained at a low price.

By the way, although quick lime was described to have a high melting temperature, it was nevertheless possible to melt it because it contained iron oxide and alumina, especially when a large amount of iron oxide was fused. In such a case, it becomes easy to melt due to the formation of calcium ferrite.

The solid solution calcium ferrite is
It can also be produced by a vertical furnace such as a cupola or a shaft furnace. In this type of furnace, coke charged together with the raw material is burned with rising air and the raw material is melted by the heat, so granulation is performed in advance so that the raw material is not taken away by the combustion gas There is a need. As a raw material, a mixture of lime, iron oxide, and alumina, which have been pulverized in advance, is used so as to have a composition of quicklime 25 to 40% by weight, iron oxide 50 to 70% by weight, and alumina 2 to 10% by weight.

Also in this case, quicklime or limestone may be used as the lime. However, unlike a reverberatory furnace or the like, it is not preferable to use a class of limestone in which pulverization proceeds easily, and it is necessary to pay attention to the loss due to combustion gas. By the way, provided that such granulation is performed, carbide slag or lime cake can be used instead of lime. For the former, Ca (OH) ₂
This is because 90% or more is contained, and the latter is composed of fine CaCO ₃ . It should be noted that the solid solution calcium ferrite is crushed to a size of 5 to 30 mm for use, which is not different from the previous example.

As the above-mentioned iron oxide, a mill scale of a rolling mill or a scale coming out of a heating furnace may be used, but sinter, iron sand, iron ore, etc. may be used. Anything is good. Aluminum ash (refined aluminum ash) or bauxite may be used as the alumina.

Incidentally, the conventional dephosphorization by calcium ferrite has a composition slightly CaO-like even when considered from the equilibrium diagram in consideration of the subsequent desulfurization reaction. That is, it should be noted that the mixing ratio of CaO was higher than that of Fe ₂ O ₃ , but the present invention is completely opposite thereto.

In the operation shown in FIG. 1A, hot metal that has not been desiliconized is transferred to a topped car 3 for desulfurization, and the desulfurized hot metal 7 is charged into a converter. When oxygen is supplied by blowing, silicon Si in the molten metal is first oxidized and
It becomes O ₂ . Calcium ferrite first oxidizes phosphorus in the molten metal, even though CaO has been introduced. When the melting of CaO is promoted by calcium ferrite, SiO ₂ reacts with CaO to form 2CaO · SiO ₂ , and P ₂ O ₅ turns into nCaO · P ₂ O ₅ and is fixed to the slag.

The basicity of the final slag after decarburization is increased to 3.5 to 4.5 by adding quicklime CaO as necessary.
In such a case, the conditions for suppressing the rephosphorization and maintaining the melting of CaO are more and more prepared. After that, decarbonization can be performed by blowing oxygen in the converter. Calcium ferrite also contains Al ₂ O ₃ , which lowers the melting point of the slag-making agent to promote slag-forming activity, contributes to slag stabilization, and facilitates high-temperature decarburization and cleaning. And

By the way, the reason for the basicity being 3.5 to 4.5 is that if the basicity is 3.5 or less, the phosphorus is easily restored, and if the basicity is 4.5 or more, excess CaO is not contained in the slag. This is because the slag remains as reactive lime, and the slag is easily swelled and the fluidity of the slag is lowered.

As described in the section of the prior art, although mill scale and fluorite are added for dephosphorization, 30 to 35 kg of CaO is consumed per ton of molten steel. If calcium ferrite is charged at 12 to 13 kg / ton, Ca
O only needs to be about 10 kg / ton. If the dephosphorization time is 5 minutes and the decarburization time is 30 minutes, the dephosphorization rate, which was conventionally only 85%, could be improved to 94%.

In addition, since fluorite is not used in the present invention, even if slag is used as a fertilizer, there is no danger of causing environmental destruction due to fluorine, and there is no factor causing secondary damage. In addition, the total amount of the slag-making agent is reduced, and as a result, the amount of slag is reduced.

FIG. 1B shows an example in which the desulfurized molten metal 7 has been desiliconized in advance. As described in the section of the related art, the silicon is often desiliconized in the blast furnace cast floor 8 by supplying an oxide or the like. In the case where pig iron with a small amount of silicon can be melted in the blast furnace 1, the method may be performed as shown in FIG.
If pig iron containing a lot of silicon is melted, desiliconization is also carried out before dephosphorization as in (b), so that the dephosphorization reaction can be promptly advanced, which is convenient.

FIG. 2 (a) shows an example in which the dephosphorized slag is discharged after dephosphorization and then decarburized. Quick lime 10 is added to the dephosphorized molten metal 9 to generate decarburized slag 11, and the converter 4 for dephosphorizing the molten metal 7 is simultaneously or immediately before or immediately after, preferably immediately before, the molten decarburized slag 11. Is charged with calcium ferrite 6. In this case, depending on the composition of the decarburized slag, it may be better to add some quick lime.

FIG. 2B shows an example in which the molten metal 7 has been desiliconized in the blast furnace cast floor 8 in advance. In both (a) and (b), the calcium ferrite melts between the melting decarburized slags to create a low temperature melting zone. Therefore, the calcium ferrite and the phosphorus in the molten metal proceed at once in a portion where the dephosphorization environment is prepared. Of course, if the iron oxides FeO and Fe ₂ O ₃ contained in the molten decarburized slag 11 are large, the progress of dephosphorization can be achieved by this.

Since the dephosphorized slag 12 is discharged before decarburization, it can be used as phosphorus fertilizer or the like. Since the decarburized slag 11 is used for dephosphorization, the amount of waste is significantly reduced. By the way, in FIG.
Is transferred to another converter 13 for decarburization, and the decarburized slag 11 is charged together with the calcium ferrite 6 into the converter 4 containing the molten metal 7. However, if it is desired to decarburize in the dephosphorized converter 4, the dephosphorized slag is slagged, then quick lime is charged and decarburized. Ferrite may be charged.

Incidentally, when steel containing a large amount of carbon is melted, the amount of iron oxide in the decarburized slag is small, and therefore, the amount of calcium ferrite is, for example, 0.9 to 1.3 times the weight (weight) of the decarburized slag. Input. When smelting steel with a small amount of carbon, the amount of iron oxide contained in the decarburized slag increases.
In any case, a phosphorus removal effect can be sufficiently exerted by inputting an amount of 1.0 to 1.0 times.

FIG. 3A shows another example in which dephosphorized slag is discharged after dephosphorization and then decarburized. Quicklime 10 is added to the dephosphorized molten metal 9 to produce decarburized slag 11. However, unlike the case of FIG. 2, iron oxide 14 is added to the molten decarburized slag 11, and the iron oxide added molten decarburized slag 11A is brought into contact with the molten metal 7 to be dephosphorized. Also in this example, the flow of FIG.

FIG. 3 shows the dephosphorized slag 1 by tilting the converter 4.
2 is discharged, the molten metal is transferred to another converter 13 and quicklime 10 is put therein, and after the decarburization is completed, steel is removed from the converter 13.
Thereafter, the decarburized slag 11 is transferred to a waste pan (not shown), into which iron oxide 14 is placed, and then charged into the converter 4 containing the molten metal 7 to be dephosphorized.

However, the present invention is not limited to such an example. For example, iron oxide is put into the decarburized slag in the converter in which the converter 13 is tilted to produce steel, and the posture is returned, and the converter 13 is dephosphorized. The molten metal 7 to be poured can be poured. In any case, it is necessary to determine the amount of iron oxide to be charged by checking the amount of CaO remaining in the decarburized slag.
When dephosphorizing lime, it is desirable not to add quick lime as shown in FIG.

An example of the component composition of the converter slag after the decarburization is completed is as shown in A-1 to A-4 in Table 1.

[Table 1]

For example, the slag of A-1 CaO, Al ₂ O
Paying attention to ₃ , FeO, and Fe ₂ O ₃ , the results are as shown in the first row A in Table 2.

[Table 2] An example in which iron oxide is added to this converter slag “A” will be described. The column of B is a composition ratio when "A" is converted to 100%. Column C shows that half of the CaO was applied to the subject of calcium ferrite formation.
This is converted to 100% in the column of D, and the composition added with 16.0% by weight of iron oxide to the configuration is in the column of E. This is a column of F converted to 100%, and CaO is 2
5 to 40% by weight, iron oxide 50 to 70% by weight,
Alumina has a composition of 2 to 10% by weight.

It is assumed that 1,000 kg of "A"
-1 "slag (decarburized slag)
O weighs 538 kg. If iron oxide is added to half of this 269 kg CaO, 269 / 47.8 = y /
What is necessary is to input y = 77.1kg which satisfies 13.7 (refer to the column of F for 47.8 and 13.7).

FIGS. 1 to 3 show an example in which desulfurization is carried out before dephosphorization. However, hot metal produced from iron ore having a low sulfur content may not be sufficient for desulfurization. The desulfurization may be performed as needed.

By the way, when stainless steel is melted, chromium sometimes remains on the furnace wall. When this melts into a newly charged molten metal for the purpose of melting another steel type, the behavior of the chromium in the molten metal is often similar to the slagging process of phosphorus. Therefore, according to the method of the present invention, it is also possible to perform the dechromization together with or independently of the dephosphorization.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a treatment process to which a dephosphorization method of a molten metal according to the present invention is applied. FIG. 1 (a) is a treatment process diagram for dephosphorizing a molten metal which has just been desulfurized, and FIG. FIG. 9 is a processing process diagram when processing is also performed.

FIG. 2 is a dephosphorization process in the case of removing dephosphorized slag and then decarburizing after dephosphorization, and FIG. 2 (a) is a process diagram in the case of dephosphorizing molten metal that has just been desulfurized; (b) is a process diagram when the molten metal has been subjected to a desiliconization process in advance.

FIG. 3 is a diagram showing a different dephosphorization process in the case where dephosphorized slag is discharged and then decarburized after dephosphorization, and FIG. (B)
Fig. 3 is a process diagram when the molten metal is also subjected to a desiliconization process in advance.

[Explanation of symbols]

4: Converter (metal refining furnace), 5: quicklime, 6: calcium ferrite, 7: desulfurized molten metal, 9: dephosphorized molten metal, 10: quicklime, 11: decarburized slag, 12: dephosphorized slag, 14: oxidation iron.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akira Iwami 7-1-26-1 Nishinakajima, Yodogawa-ku, Osaka-shi, Japan Inside Nippon Material Co., Ltd. 2252 No. Nakayama Lime Industry Co., Ltd. F term (reference) 4K001 AA10 BA02 BA05 BA12 BA14 CA26 EA07 GA03 GA06 GA13 KA01 KA05 KA06 4K013 BA02 BA03 CA04 CB02 CB09 CF12 DA03 DA10 EA02 EA03 EA05 4K014 AA03 AB02 AB03 AD04 AC03 AB03 AB06 AB11 AC03 AC13 AC14 AC16 AC17 AC34 AC36 BA12 BB02 BC02 DA07 EA03 EA14 EA27

Claims (7)

[Claims] In a slagging method using a lime-based flux that reacts with phosphoric acid contained in a molten metal in a metal smelting furnace to promote slag generation, calcium and calcium are added to the molten metal to be dephosphorized and decarburized. A method for dephosphorizing a molten metal, comprising adding ferrite and an amount of quicklime to finally produce a slag having a basicity of 3.5 to 4.5. 2. In a slagging method using a lime-based flux that reacts with phosphoric acid contained in a molten metal in a metal refining furnace to promote slag generation, the dephosphorized slag is discharged after dephosphorization. When decarburizing from
During the decarburization period, quick lime is added to form decarburized slag, and the molten decarburized slag is brought into contact with the molten metal to be dephosphorized, and calcium ferrite is added at that time. Phosphorus method. 3. A slagging method using a lime-based flux that reacts with phosphoric acid contained in a molten metal in a metal smelting furnace to promote slag formation. When decarburizing from
In the decarburization period, quick lime is added to generate decarburized slag, iron oxide is added to the molten decarburized slag, and the iron oxide added molten decarburized slag is brought into contact with the molten metal to be dephosphorized. Dephosphorization of molten metal. 4. The calcium ferrite according to claim 1 or 2 is mainly composed of quicklime 25 to 4
A low-temperature slag-forming dephosphorizing agent having a composition of 0% by weight, 50 to 70% by weight of iron oxide, and 2 to 10% by weight of alumina. 5. A lime, an iron oxide and an alumina are charged into a reverberatory furnace or an electric furnace so as to have a composition ratio as described in claim 4, and then melted. A method for producing a low-temperature slag-forming dephosphorizing agent, which comprises crushing into pieces. 6. The low-temperature slag-forming dephosphorizing method according to claim 5, wherein the lime is limestone having crystal particles of 10 μm or more, having a small thermal expansion absorption capacity, and powdering when heated. Method of manufacturing the agent. 7. A mixture obtained by mixing lime, iron oxide, and alumina, which have been pulverized in advance so that the composition ratio described in claim 4 is obtained, and granulating the granulated material. 5 to 30mm of solid solution calcium ferrite
A method for producing a low-temperature slag-forming dephosphorizing agent, which is largely crushed.