KR100681292B1 - Method of manufacturing low phosphorous hot metal - Google Patents

Abstract

An object of the present invention is to perform an effective dephosphorization treatment with a small amount of refiner added without adding a large amount of CaF ₂ . According to the present invention, by supplying gaseous oxygen and a refining agent to a molten iron bath surface in a specific form under conditions in which the amount of slag after treatment is considerably reduced compared to the prior art, extremely efficient dephosphorization and refining using an uneven molten state of slag is possible. It was made to find out that the dephosphorization treatment was carried out by blowing gaseous oxygen and at least a part of the refining agent into the molten iron bath through the upper lance, and the slag amount after the treatment was 30 kg / melting ton or less, preferably 20 kg /. It is set to the molten metal ton or less, More preferably, it is 10 kg / molten iron or less. More preferably, Si content is 0.15 mass% or less, Preferably it is 0.07 mass% or less, Especially preferably, dephosphorization process is performed with respect to molten iron of 0.003 mass% or less.

Low citation, dephosphorization, molten iron preliminary treatment, refining agent, slag, dephosphorization.

Description

METHODS OF MANUFACTURING LOW PHOSPHOROUS HOT METAL             

TECHNICAL FIELD This invention relates to the method for efficiently manufacturing a low phosphorus ship by the dephosphorization process performed as molten iron preliminary process.

Instead of the conventional converter method, the molten iron preliminary treatment method of performing dephosphorization treatment in the molten iron phase has become widely available. This is because the lower the refining temperature, the easier the dephosphorization reaction is to proceed thermodynamically, and the dephosphorization treatment can be performed with a smaller amount of refining agent.

In general, in the molten iron preliminary treatment, first, a solid oxygen source such as iron oxide is added to the molten iron and subjected to de-silification treatment, the slag generated in the de-silification treatment is removed, and then a refining agent is added. Dephosphorization treatment is carried out. Usually, CaO type refiners, such as lime, are used as a dephosphorization refiner, and a solid oxygen source (iron oxide etc.) and gaseous oxygen are used as an oxygen source. As the processing container, a topedo car, a ladle (charging ladle), a converter container, or the like can be used. In addition, the addition of CaF ₂ (fluorite) is widely practiced for promoting the regeneration of CaO-based refining agents.

As the dephosphorization treatment conditions of the prior art, for example, in Japanese Patent Application Laid-Open No. H7-70626, the slag basicity is 0.6 or more and 2.5 or less, and the treatment end temperature is 1250 ° C or more and 1400 ° C or less, and the low blowing agitation force 1. Okg / melting tonne or more, oxygen supply rate 2.5Nm ³ / melting tonne or more is disclosed. In this technique, the slag basicity is 2.5 or less, and since the slag fluidity deteriorates with the basicity above, dephosphorization requires processing at an unfavorable high temperature. In addition, when it is 2.5 or less, dephosphorization advances that the slag basicity is higher.

In addition, Japanese Patent Application Laid-Open No. 8-311523 introduces CaO powder and oxygen of 0.7 to 2.ONm ³ / min / melting ton through a top blowing lance with respect to the molten iron in the converter type vessel. At the same time, there is disclosed a method of blowing a stirring gas of 0.05 to 0.30 Nm ³ / min / melting ton from the furnace or sidewall of the converter type container. By optimizing the amount of oxygen supplied in i), rapid production of slag (goods of CaO) and FeO concentration in slag are intended, and efficient dephosphorization treatment is possible.

In the conventional molten iron dephosphorization and refining technique, including the above-mentioned Japanese Patent Application Laid-Open No. Hei 7-70626 and Hei 8-311523, the slag after the treatment is uniformly melted, as can be seen from the discussion using the dephosphorization equilibrium form. It is assumed that slag-metal is close to equilibrium. For this reason, slag dephosphorization ability (phosphorus distribution Lp = mass% (P) / mass% [P], mass% (P): P concentration in slag, mass% [P]: P concentration in metal), and slag volume (slag volume) is also determined under such a premise, and the operation is performed.

The slag distribution Lp depends on the slag basicity, and the higher the slag basicity, the higher the phosphorus distribution Lp. However, conventionally, when the slag basicity becomes high, the fluidity of slag deteriorates and it is considered that it becomes an unfavorable condition for dephosphorization. On the other hand, when the slag basicity is lowered, the phosphorus distribution Lp is lowered. Therefore, it is necessary to add a large amount of lime (addition of SiO ₂ source (SiO ₂ source) as necessary) to increase the slag amount.

In view of the above, in the prior art, the slag basicity necessary for securing a predetermined phosphorus distribution Lp is set, the amount of slag necessary to reach the target P under the slag basicity is determined, and the addition of a refining agent is performed. Since the slag basicity cannot be increased very much from the relation of, in the normal dephosphorization treatment in which the Si content is carried out to around 0.2% by mass of molten iron, the slag amount (the amount of slag after the treatment) is about 40 to 50 kg / melting ton. This is done. For example, in Japanese Patent Application Laid-Open No. Hei 8-311523, the amount of CaO (refining agent) can be determined depending on the P content in the molten iron to be dephosphorized, and in the case where the P content before the treatment is about 0.10% by mass, It is said that about 20 kg / mol ton of CaO is added, but the slag present in the refining vessel during dephosphorization is SiO ₂ produced by the degreasing reaction of the molten iron with respect to the slag powder produced by the injected CaO. Powder, P ₂ 0 ₅ minutes produced by dephosphorization reaction, slag powder (FeO, MnO, etc.) generated from other molten iron components, slag powder brought in from the previous process, and melting loss of the furnace body. ) Slag powder (A1 ₂ 0 ₃ , MgO, etc.), slag powder originally attached to the furnace body, slag powder attached to the input scrap, and slag powder generated from the added ore, etc. In general, Since the amount of slag (the amount of slag after treatment) is about 2 times to about 2.5 times the amount of added CaO, when the amount of CaO of about 20 kg / melting ton is introduced as described above, the amount of slag after treatment is inevitably 40 to It reaches about 50kg / molton.

Recently, from the viewpoint of environmental protection and the like, it is required to reduce the slag amount generated in the refining process including the dephosphorization step as much as possible. However, in the above-described prior art, there is a limit to the reduction of the slag amount. We cannot fully respond to the request of reduction.

Further, in the addition of CaF ₂ for promoting goods of the refiner, in recent years, and F are considered the environmental impact, it also is to request to reduce as much as possible the amount of CaF ₂ in the Steel refining, by CaF ₂ was added There is also a limit to improving the dephosphorization efficiency.

Disclosure of the Invention

It is an object of the present invention to provide a method for producing a low-phosphorus vessel that can efficiently dephosphorize with a small amount of refiner added without adding a large amount of CaF ₂ , thereby reducing the amount of slag generated as much as possible.

In the dephosphorization and refining of the molten iron, an oxygen source and a CaO source refining agent are added to the molten iron, but as a method of supplying the oxygen source, it is possible to effectively control the temperature drop and to promote the formation of FeO. A method of blowing gaseous oxygen into the molten iron bath surface from the lance is appropriate. In this oxygen supply method, the slag is pushed out by the energy of gaseous oxygen in the refining vessel, and the bath surface (bath surface of the molten iron) is exposed, and the other surface is It is divided into parts covered with slag, so that the state of slag in the refining vessel is not uniform. Here, the present inventors do not stick to the conventional idea of keeping slag in a uniform molten state in a refining container, and the dephosphorization refining method that can stabilize the dephosphorization efficiency at a high level with a small amount of refining agent added. As a result, as a result, gaseous oxygen and a refining agent were specified under conditions in which the amount of slag after treatment was considerably reduced as compared with the prior art, and more preferably under conditions in which the Si content in the molten iron before treatment was below a predetermined level. It has been found that by supplying the furnace to the molten iron bath surface, in contrast to the conventional idea of melting the slag uniformly, very efficient dephosphorization and refining using the uneven molten state of the slag is possible.

The manufacturing method of the low citation ship of this invention was made | formed based on such knowledge, The characteristic is that adding the refiner which is oxygen source and CaO source in the container which has molten iron, and performs dephosphorization process which is a molten iron preliminary process. In the method for producing a low squirrel vessel, dephosphorization treatment is carried out by blowing gaseous oxygen and at least a part of a refining agent into the molten iron bath surface through a top blowing lance, and at the same time, the slag amount after the treatment is 30 kg / molten ton or less. Further, more preferable slag amount after treatment is 20 kg / melting ton or less, in particular 10 kg / melting ton or less. According to this invention method, by using the mechanism of direct dephosphorization reaction in the molten iron bath area | region to which gaseous oxygen is blown, and fixation of P by solid-state slag in the outer region, Efficient dephosphorization can be performed with a small amount of refiner added without adding a large amount of CaF ₂ .

In order to make the effect of this invention more effective, it is preferable to perform a dephosphorization process with respect to low Si molten iron. That is, it is preferable to perform dephosphorization treatment on molten iron whose Si content is 0.15 mass% or less, preferably 0.07 mass% or less, particularly preferably 0.03 mass% or less, whereby the dephosphorization reaction by the mechanism is stably generated. Optimal conditions are given.

In addition, as an addition form of the refiner supplied from the upper lance to the molten iron bath surface, it is preferable that at least a part of the refiner supplied from the upper lance is blown into the molten iron bath surface region into which gaseous oxygen is blown, and more preferably, the upper lance It is preferable that at least a part of the refining agent supplied from is blown into a hot spot generated in the molten iron bath surface by blowing of gaseous oxygen. In addition, particularly preferably, at least a part of the refining agent is preferably blown into the molten iron bath surface using gaseous oxygen as a carrier gas. As a result, the refining agent can be efficiently recycled in the molten iron bath surface region in which a large amount of FeO is generated by the supply of gaseous oxygen, and the dephosphorization reaction can be effectively promoted.

In the present invention, an effective dephosphorization treatment can be carried out under the condition that CaF ₂ is added in an amount of 2 kg / molton or less or CaF ₂ is not substantially added.

In the present invention, it is preferable to dephosphorize and refine the molten iron having a P content of 0.10% by mass or less to a P content (a component specification value of steel) required for rough steel, and in particular, the P content in the molten iron after the dephosphorization treatment is 0.010 mass. It is preferable that it is% or less. Thereby, in the converter smelting performed continuously, only substantial decarburization refining can be performed, without using a slag seed material substantially.

In the present invention, various preferred embodiments as described below can be adopted under the above basic conditions.

In the first embodiment, the feed rate B (kg / min / melting ton) in terms of CaO, which is a refining agent blown into the molten iron bath surface, and the feed rate A (Nm ³ / min / melting ton) of gaseous oxygen injected into the molten iron bath surface. The dephosphorization treatment is performed to satisfy the following formula (1), preferably the following formula (2). As a result, the balance between the amount of FeO generated and the amount of CaO supplied by the supply of gaseous oxygen is optimized, and a higher dephosphorization efficiency can be obtained.

0.3? A / B? (One)

1.2? A / B? (2)

In the second embodiment, a ladle-type or topedo-car-type container is used as a container holding the molten iron, and the gaseous oxygen and at least a part of the refining agent are blown into the molten iron bath surface through an upper lance. At the same time, dephosphorization treatment is performed by blowing gas containing powder into the molten metal through an immersed lance or / and a blowing nozzle. Thereby, in the dephosphorization process using a ladle-type or topidoca type | mold container, moderate stirring action of molten iron | metal can be obtained, and higher dephosphorization efficiency can be obtained.

In this second embodiment, it is preferable that the powder blown into the molten iron through the immersion lance or / and the blowing nozzle is part of the refining agent, and the amount of gaseous oxygen blown into the molten iron bath surface through the upper lance is 0.7 Nm ³ / min / It is preferable that it is below a molten metal ton. In addition, it is preferable to blow 80 mass% or more of the amount of the refiner added by the dephosphorization treatment into the molten iron bath surface through the upper suction lance in addition to performing an efficient treatment. In addition, in the case where the total amount of the refining agent is added by blowing into the molten iron bath surface through the upper suction lance and by blowing into the molten iron through the immersion lance or / and the blowing nozzle, It is preferable to set it as 20-80 mass% of the total addition amount of a refiner | purifier, and the effect by injecting a refining agent into a molten iron bath surface, and the stirring effect of molten iron by blowing in molten iron | metal are obtained in a balanced manner.

In the third embodiment, the dephosphorization treatment is performed so that the supply rate of the refiner blown into the molten iron bath surface and the gas oxygen supply rate satisfy the conditions of the following formulas (3) and (4). Thereby, the unnecessary amount of the refiner is not added in the latter stage of the dephosphorization treatment, and the treatment with the required minimum refiner added is carried out, so that more efficient dephosphorization treatment can be performed with a small amount of refiner added.

(C1 / D1)> (C2 / D2)... (3)

C1> C2... (4)

However, C1: Average value of refining agent supply rate in terms of CaO in the dephosphorization treatment (kg / min / melting ton)

   C2: Average value of refining agent feed rate in terms of CaO in the latter stage of dephosphorization (kg / min / melting ton)

D1: Average value of gaseous oxygen feed rate in dephosphorization (Nm ³ / min / melting ton)

D2: Average value (Nm ³ / min / melting ton) of gaseous oxygen supply rate in post dephosphorization treatment

In this third embodiment, the refining agent supply rate and the gas oxygen supply rate in terms of CaO can be changed continuously or in stages during the dephosphorization treatment period.

In the fourth embodiment, the molten iron having an Si content of 0.1% by mass or less is blown into the molten iron bath surface by blowing gaseous oxygen and at least a part of the refiner into the molten iron bath surface through a top blowing lance. , a refiner, to 5 lime amount to be calculated by the formula W _cao _P (kg / hot metal ton) and the following (6) a lime amount W _cao _Si (kg / hot metal ton) an amount of lime total being calculated by the formula Add. Thereby, efficient dephosphorization treatment can be performed with the minimum necessary refiner addition amount.

W _cao _P = (melting line [P]-target [P]) x (10/62) x 56 x 3 / η _cao . (5)

However, molten iron [P]: P concentration (mass%) in molten iron before dephosphorization treatment

    Target [P]: P concentration (mass%) in molten iron | metal after target dephosphorization treatment.

η _cao (lime efficiency) = 0.5 to 1

W _cao _Si = molten iron [Si] x (10/28) x 56 x 2. (6)

However, molten iron [Si]: Si concentration (mass%) in molten iron before dephosphorization treatment

In the embodiment of the fourth, lime amount W _cao _P to blow at least 80% by weight lime to the molten iron bath surface through the sangchwi lance (where, η _cao = 1 W _cao _P which is obtained in), for performing the efficient processing In addition, it is preferable. In addition, as a refining agent corresponding to the amount of lime W _cao _Si, at least one selected from a steel slag containing lime powder, calcined lime, calcareous lime, and unreacted CaO may be used. Can be.

In 5th Embodiment, the depth L of the recessed part formed in a molten metal bath surface by the blowing of gaseous oxygen or blowing of the refiner which makes gaseous oxygen a carrier gas defined by following formula (7) is controlled to 200-500 mm. Thereby, the mode of supply of gaseous oxygen to the hot spot which is a reaction site is optimized, and more efficient dephosphorization treatment can be performed with a small refiner addition amount.

L = L ₀ × exp {(-0.78 × L _H ) / L _o }... (7)

L ₀ = 63 × {(F ₀₂ / n) / d _t } ^2/3

However, L _H : Lance height of upper lance (mm)

F ₀₂ : Gas Oxygen Supply Rate from Upper Lance (Nm ³ / hr)

    n: Nozzle air of the upper lance

d _t : Nozzle diameter of nozzle lance (nozzle 孔徑, mm) (However, if the nozzle diameters of a plurality of nozzle holes are different, average nozzle diameter of all nozzle holes)

In the embodiment 6, a part in terms of Si content is not substantially added to 1kg of the amount of CaF ₂ / hot metal ton or less, or CaF ₂ with respect to the molten iron of more than 0.15 mass%, and the oxygen gas through the sangchwi lance at least The dephosphorization treatment is performed by blowing the scouring agent into the molten iron bath surface, and the molten iron temperature at the end of the dephosphorization treatment is 1360 ° C to 1450 ° C. Thereby, an efficient dephosphorization process can also be performed also in high temperature process, and the heat margin in a post process can fully be ensured.

In the seventh embodiment, a substance that absorbs heat of molten iron by chemical reaction and / or pyrolysis reaction is supplied to the molten iron bath surface region to which gaseous oxygen is supplied. Thereby, since the temperature rise of the molten iron bath surface area | region to which gaseous oxygen is supplied is suppressed without the goods of a refiner being inhibited, higher dephosphorization efficiency can be obtained.

In this seventh embodiment, it is preferable to supply at least a part of the substance that absorbs heat of the molten iron by chemical reaction and / or pyrolysis reaction to the hot spot generated in the molten iron bath surface by blowing gaseous oxygen. The material that absorbs heat of the molten iron by chemical reaction and / or pyrolysis reaction is preferably at least one selected from carbon dioxide, water vapor, nitrogen oxides, metal carbonates and metal hydroxides, and in particular, CO is one or more species selected from ₂ or the metal carbonate to generate H ₂ 0, CO _2, or a metal hydroxide to generate a H ₂ 0 by the thermal decomposition is preferred. Further, among others, CaCO _3, preferably _{Ca (OH) 2, CaMg (} CO 3) at least one species selected from among _2.

In this seventh embodiment, in the molten iron bath area to which gaseous oxygen is supplied, instead of part or all of the refining agent which is a CaO source, the heat of the molten iron is absorbed by the chemical reaction and / or pyrolysis reaction. As a substance to be used, one or more selected from CaCO ₃ , Ca (OH) ₂ and CaMg (CO ₃ ) ₂ may be supplied. In this embodiment, at least one selected from CaCO ₃ , Ca (OH) ₂ , and CaMg (CO ₃ ) ₂ is preferably supplied to a hot spot generated in the molten iron bath surface by blowing gaseous oxygen.

The first to seventh embodiments of the method of the present invention described above may be performed alone, or may be performed by arbitrarily combining the conditions of two or more embodiments. The effect is higher.

Detailed description of the invention

The CaO added into the deionized popular phrase, refining vessel of the hot metal has been the conventional thinking, by generating SiO _2, reacts with FeO solution heat melting that is, by the supply of oxygen, CaO-SiO ₂ - FeO based homogeneous and also Goutal of It is said that slag of toughness is produced and dephosphorization of molten iron advances by reaction of this slag and P in molten iron | metal. On the premise of such dephosphorization mechanism, as described above, the slag basicity is determined in consideration of the fluidity and dephosphorization ability of the slag, and the amount of slag necessary to reach the target P under the slag basicity is determined. On the other hand, the inventors of the present invention, under conditions in which the amount of slag after treatment is considerably reduced as compared with the prior art, more preferably under conditions in which the Si content in the molten iron before treatment is below a predetermined level, the gaseous oxygen and the refining agent are subjected to an upper lance. By employing a treatment method that blows into the molten iron bath surface, it has been found that dephosphorization and refining can be performed very efficiently by a mechanism completely different from the prior art.

EMBODIMENT OF THE INVENTION Hereinafter, the detail and preferable embodiment of this invention based on such knowledge are demonstrated.

In the method of the present invention, a gaseous oxygen and at least a part of the above-mentioned gaseous lance are prepared by adding a scavenger, which is an oxygen source and a CaO source, in a vessel (refining vessel) having molten iron, and then producing a low quenching vessel by performing dephosphorization treatment, which is a molten iron preliminary treatment. The refining agent was blown into the molten iron bath surface and dephosphorized. When gaseous oxygen is blown into the molten iron bath surface through the upper bleeding lance, a large amount of FeO is generated by the gaseous oxygen colliding with the bath surface, which is a very advantageous condition for promoting the refining of the refining agent. By directly supplying the refining agent through the upper lance, the goods of the refining agent (CaO) can be effectively promoted.

In addition, in the blowing of gaseous oxygen and the refiner into the molten iron bath surface by the upper lance, the refiner may be blown into the molten iron bath surface using a carrier gas other than gaseous oxygen (for example, inert gas such as N ₂ or Ar). Also in that case, it is preferable to blow part or all of the refining agent into the molten iron bath surface area | region which gas oxygen is supplied (blown). This means that the molten iron bath area where gaseous oxygen is supplied is the place where FeO is generated by oxygen supply, and by adding CaO directly to the bath area, the CaO goods are promoted effectively and the contact efficiency between CaO and FeO is increased. Because. Moreover, it is most preferable to supply a refining agent to the area | region called "hot spot" which arises especially from the molten iron bath surface area | region supplied with gaseous oxygen, and gas gas uptake. This hot spot is a molten iron bath surface area which becomes the highest temperature due to collision of gaseous oxygen gas jets, but is a region in which oxidation reaction by gaseous oxygen is concentrated and stirred by gaseous oxygen gas jet. It can be said that it is the area | region which can acquire the effect by the most remarkably. In this sense, it is preferable to use gaseous oxygen as a carrier gas for blowing the refiner into the molten iron bath surface, and in this case, the gaseous oxygen is blown into the molten iron bath surface together with the refiner so that the refiner can be directly supplied to the hot spot. As a result, the contact efficiency of CaO and FeO in the molten iron bath surface is the highest.

In the method of the present invention, in such an addition form of gaseous oxygen and a refining agent, an object is to generate an efficient dephosphorization reaction by the following basic mechanism.

In other words, when a refining agent (CaO) is blown into the molten iron bath area (preferably a hot spot) in which gaseous oxygen is optimally supplied, the CaO reacts rapidly with FeO generated in the hot spot and melts. (Goods) to form a fusion of CaO-FeO system. The generated CaO-FeO fusion is pushed from the molten iron bath surface to which gaseous oxygen is supplied centering around the hot spot by the kinetic energy of the gaseous oxygen to the area | region with low oxygen potential, After the reaction, FeO is reduced to form a stable solid phase such as 2CaOSiO ₂ depending on the Si content in the molten iron before treatment. When the Si content in the molten iron decreases to some extent in accordance with the above reaction, the CaO-FeO-based melt next starts to react with phosphorus to form a similarly stable solid phase of 3CaO.P ₂ O ₅ . As a result, a considerable amount (or most) of slag generated in accordance with the progress of the dephosphorization treatment and sequentially pushed from the molten iron bath surface area to which gaseous oxygen centered on the hot spot is supplied to the outer area thereof is 2CaO · SiO ₂ ,. 3CaO is present as a stable solid phase and of P ₂ 0 _5. And since the slag which became solid in this way is very stable, even if slag basicity is low, it will not melt again. In this way, the direct dephosphorization reaction occurs in the region centered on the hot spot, and the slag pushed outward is present in the state of the solid phase, so that dephosphorization can be performed efficiently with a small amount of refiner added.

As described above, according to the method of the present invention, the effective dephosphorization treatment is carried out by using a mechanism such as direct dephosphorization reaction in the molten iron bathing area centered on the hot spot and fixing of P by slag of the solid body in the outer region. However, by simply blowing gaseous oxygen and a refining agent into the molten iron bath surface, the dephosphorization reaction by the above apparatus cannot be realized stably. That is, in order to realize the dephosphorization reaction by the said mechanism stably, in addition to employ | adopting the specific supply form of said gaseous oxygen and a refining agent, processing under a sufficiently small slag amount, specifically, the slag amount after processing It is necessary to make 30 kg / molten tonne or less, preferably 20 kg / molten tonne or less, more preferably 10 kg / molten tonne or less. From the same point of view, the molten iron to be subjected to the dephosphorization treatment is a low Si molten iron, specifically Si content of 0.15 mass% or less, more preferably 0.07 mass% or less, still more preferably 0.03 mass% or less It is preferable that it is a molten iron.

Here, in the present invention, the reason for the treatment under the small amount of slag is as follows. In order to effectively generate the dephosphorization reaction by the above-mentioned specific mechanism, gaseous oxygen through the upper lance needs to be supplied to the molten iron bath surface by so-called soft blow (low dynamic pressure). That is, in the dephosphorization reaction by the above-described mechanism, the molten iron bath surface area to which gaseous oxygen centered on the hot spot is supplied becomes the main generation place of FeO, and CaO supplied to this area reacts with FeO to cause CaO-FeO system. The melt is formed, and the CaO-FeO melt melts directly with P in the molten iron to form a stable solid phase of 3CaO.P ₂ O ₅ . Here, in the state where the amount of slag is large and the slag layer is thickly formed as in the prior art, if the gaseous oxygen is supplied by soft blow, the gaseous oxygen jet cannot penetrate the slag layer, so that the gaseous oxygen is the molten iron bath surface. It is not properly supplied to, and production of FeO on the molten iron bath surface is insufficient, and hence the amount of CaO-FeO-based melt is reduced. On the other hand, when the gas oxygen is supplied at a hard blow (high dynamic pressure) so that the gas oxygen jet can penetrate the thickly formed slag layer, the supply region becomes a strong stirring state. Therefore, even if FeO is produced, it is reduced by C in the molten iron, and in this case as well, the required amount of FeO cannot be secured, thereby reducing the generation of CaO-FeO-based melts. If the slag amount is large in this way, even if gas oxygen is supplied to either soft blow or hard blow, the amount of FeO or CaO-FeO melts cannot be stably produced, and the dephosphorization reaction can be stably generated by the above-described mechanism. Things become difficult. Therefore, in order to properly supply gaseous oxygen to the molten iron bath surface by soft blow and to effectively generate the dephosphorization reaction by the above-described mechanism, it is indispensable to restrict the amount of slag to sufficiently reduce the thickness of the slag layer. For this reason, in this invention, it is made on condition that the amount of slag after a process may be 30 kg / melt | ton or less. From the reasons described above, the amount of slag after the treatment is preferably as small as possible, particularly 20 kg / mol or less, more preferably 10 kg / melt or less.

In the present invention, the reason why it is preferable to perform dephosphorization treatment on the low Si molten iron is as follows. As described above, in the above-mentioned specific dephosphorization apparatus, CaO which is supplied to the molten iron bathing area (= the main generation area of FeO) supplied with gaseous oxygen centered on the hot spot and reacted with FeO reacts with CaO-FeO. Dephosphorization proceeds by forming a system melt and reacting this CaO-FeO melt directly with P in molten iron, but when Si content in molten iron is high, the CaO-FeO melt produced | generated is consumed for reaction with Si, and it is mentioned above. It does not contribute enough to a direct dephosphorization reaction. Therefore, the optimum conditions for stably generating the dephosphorization reaction by the above-mentioned mechanism satisfy the above-described conditions of the slag amount after the treatment, and the Si content in the molten iron to be dephosphorized is sufficiently low. In addition, when the content of Si in the molten iron is small, the amount of SiO ₂ generated is also reduced, which is advantageous in reducing the amount of slag after treatment. For this reason, in this invention, it is preferable to perform a dephosphorization treatment with respect to molten iron of Si content of 0.15 mass% or less, More preferably, it is 0.07 mass% or less, More preferably, it is 0.03 mass% or less.

In the present invention, the amount of slag after treatment is the amount of slag existing in the refining vessel (molten vessel vessel) at the end of the dephosphorization treatment. On the other hand, the amount of slag after the treatment is calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag, tracer such as yttrium oxide or strontium oxide in the slag. (tracer) can be added, and it can obtain | require by the method of analyzing the tracer density in the slag after a process, the method of measuring slag thickness directly, etc.

Fig. 1 shows the relationship between the slag content after dephosphorization and the P content in molten iron based on the test results performed by the present inventors, and the P content in molten iron after the treatment shows the average value and the range of variation. 1, 5 kg / molten iron to 10 kg / molten iron ton, 10 kg / molten iron to more than 20 kg / molten iron ton, 20 kg / molten iron to more than 30 kg / molten iron ton, 30 kg / molten iron ton more than 40 kg / molten iron ton, 40 kg / molten iron The P content in the molten iron after dephosphorization treatment of 6 to 72 ch is calculated for each slag amount after the treatment of more than ton to 50 kg / molten ton.

In this test, the molten iron drawn out from the blast furnace is subjected to de-silification in the molten iron ladle as required in the columnar column and as necessary, followed by desulfurization in the molten iron ladle using mechanical stirring. And dephosphorization were carried out in a converter vessel (300 tons). The molten iron component before dephosphorization is C: 4.5-4.7 mass%, Si: 0.01-10.28 mass%, Mn: 0.15-0.25 mass%, P: 0.1-10 mass%, S: 0.001-0.003 mass% It was. Lime powder having a particle diameter of 1 mm or less was used as a dephosphorizing refiner, and this was blown into the molten iron bath surface using gaseous oxygen as a carrier gas through a lance. CaF ₂ was not added in the refiner. The blowing time was kept constant for 10 minutes, and nitrogen gas was supplied from 0.05 to 0.15 Nm ³ / min / melting ton from the furnace in order to stir the molten iron. The raw unit of lime and oxygen is changed by the Si content in molten iron, but both the lime and oxygen are de-silicate (dicalcium silicate: 2CaO · SiO ₂ ). ), And the value except for it was made constant at 3.5 kg / molten iron ton, 9 Nm ³ / molten iron ton, respectively. The molten iron temperature before and after dephosphorization treatment was 1250 degreeC-1350 degreeC. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag.

According to Fig. 1, the larger the amount of slag after the treatment, the higher the P content after the dephosphorization treatment, and the greater the variation on the upper limit side. On the other hand, when the slag amount after treatment is 30 kg / mol ton or less, the fluctuation on the upper limit side of the P content is greatly reduced, and the P content is at most 0.020% by mass. Further, the P content in the molten iron after the dephosphorization treatment was at most 0.015 mass% after the slag amount after treatment was 20 kg / molten ton or less, and 0.010 mass% at the maximum after the slag amount after treatment was 10 kg / molten iron or less. For the above reasons, in the present invention, the amount of slag after treatment is set to 30 kg / melting tonne or less, preferably 20 kg / melting tonne or less, particularly preferably 10 kg / melting tonne or less.

FIG. 2 shows the relationship between the Si content in the molten iron before dephosphorization treatment and the amount of slag after treatment when the test of FIG. 1 was performed. According to the same figure, when the Si content in molten iron before treatment is high, the amount of lime added increases and the amount of slag increases, which has a good correlation between the slag content and the Si content in molten iron before treatment. Here, in order to make the slag amount after treatment into 30 kg / meltton or less, it turns out that it is necessary to make Si content in molten iron | metal before dephosphorization treatment into 0.15 mass% or less. Similarly, in order to make the slag amount after the treatment less than or equal to 20 kg / melting tone, it is necessary to make the Si content in the molten iron before dephosphorization treatment to be 0.07% by mass or less, and further, to make the slag amount after the treatment be 10 kg / melting tone or less. It turns out that it is necessary to make Si content in molten iron | metal before dephosphorization treatment into 0.03 mass% or less. For the above reason, in this invention, it is preferable to perform a dephosphorization treatment with respect to molten iron of Si content of 0.15 mass% or less, Preferably it is 0.07 mass% or less, More preferably, it is 0.03 mass% or less.

On the other hand, as described above, when the Si content in the molten iron is low, the rate at which the produced CaO-FeO-based melt is consumed for reaction with Si is reduced, which promotes direct dephosphorization reaction by the CaO-FeO-based melt. An effect can be acquired, and the result of FIG. 1 is considered to reflect such an effect.

The Si content in the molten iron before the dephosphorization treatment can be adjusted as follows.

The molten iron is supplied from a molten iron manufacturing facility such as a blast furnace, but as a method of lowering the Si content of molten iron to be manufactured, the total loading of silicic acid powder is reduced by preliminary treatment of raw materials for molten iron production, Methods such as low temperature operation and coke ubiquitous charging for suppressing the silicic acid reduction reaction in the furnace are effective. Therefore, when Si content of the molten iron manufactured by the blast furnace etc. is 0.15 mass% or less, you may dephosphorize-process these molten iron without performing the following desulfurization treatment.

On the other hand, when the Si content of the molten iron manufactured by the blast furnace etc. exceeds 0.15 mass%, the silicon content in molten iron before dephosphorization is performed by carrying out de-silification process in the blast furnace column, molten iron ladle, etc. before dephosphorization treatment. The phosphorus dephosphorization treatment is performed after setting it at 0.15 mass% or less.

Usually, degreasing treatment of molten iron is carried out by adding a solid oxygen source or gaseous oxygen to the molten iron. For example, a solid oxygen source such as a sintered powder or a mill scale is applied to the molten iron bath surface. The method of adding by top-charging or blowing into a bath, or adding gaseous oxygen by blowing into a molten iron bath surface or into a bath is employ | adopted.

Further, the degreasing treatment of the molten iron may be performed by adding an oxygen source to the molten iron from the blast furnace column or the molten iron ladle, for example, to the conveying vessel such as the molten iron ladle. have. In addition, in order to increase the desulfurization efficiency, by adding a stirring gas into the molten iron in the vessel or by adding a CaO source such as slaked lime to adjust the salting degree of the slag, the iron oxides in the desulfurizing slag can be reduced to the maximum, thereby increasing the reduction efficiency. have.

When the dephosphorization treatment is carried out through the molten metal degreasing treatment, it is preferable to exclude slag such as de-silicone slag in advance and to suppress the mixing of silicic acid powder as much as possible in addition to performing an effective dephosphorization treatment. For this reason, after slag is separated from molten iron by a mechanical exhaust apparatus or manual labor, dephosphorization is performed before dephosphorization.

In the method of the present invention, there is no particular limitation on the method of blowing gaseous oxygen and a refining agent into the molten iron bath surface by using the upper lance, and for example, the gas from a part of the lances of the plurality of lances of the upper lance. Refining agents may be supplied to the molten iron bath surface only using oxygen as a carrier gas from other lances as gas or gas other than gaseous oxygen (for example, inert gas such as nitrogen or Ar). Thereby, a refiner can be added to the molten iron bath surface area | region to which gaseous oxygen is supplied. In this case, gas oxygen is discharged from the main lance by using a main lance with a main lance in the center of the lance tip and a plunging lance having a plurality of secondary lances around the lance. It is particularly preferable to supply the refining agent to the molten iron bath surface by using gaseous oxygen or gases other than the above-described gaseous oxygen as carrier gases. In addition, blowing of gaseous oxygen and blowing of the refiner which makes gas other than gaseous oxygen or gaseous oxygen mentioned above as a carrier gas may be performed using another upper lance. In any of these cases, however, in order to most efficiently refining the refining agent as described above, the carrier gas of the refining agent is particularly preferably gaseous oxygen.

The gaseous oxygen used in the present invention may be either pure oxygen gas or oxygen-containing gas. As the oxygen source added to the refining vessel, in addition to gaseous oxygen, a solid oxygen source such as iron oxide (for example, sintered powder or mill scale) can be used, and these may be arbitrarily selected, such as charging a tooth or injection into a bath. It can be added by the phosphorus method. However, in order to perform efficient molten metal removal by supplying (blown) gas oxygen to the molten iron bath surface as described above, 50% or more, preferably 70% or more of the oxygen source added in the refining vessel (gas oxygen) It is preferable that converted amount) is gaseous oxygen supplied to a molten iron bath surface through a top blowing lance.

On the other hand, a part of gaseous oxygen may be supplied to the bath by a method other than blowing into the molten iron bath surface, for example, by immersion lance, spraying into the molten iron bath through a blow nozzle provided on the side wall or bottom of the molten iron container. good.

As the refining agent, a CaO refining agent (a refining agent mainly composed of CaO) such as lime is usually used. In addition, the refining agent blown into the molten iron bath surface through the upper lance uses powder.

In addition to the blowing into the molten iron bath surface by the upper lance, the refining agent may be added in part by the loading of the moist tooth, the injection into the bath, or the like, in which case, the amount of the refining agent added by these methods is 20 It is preferable to set it as mass% or less. When the ratio of the refiner added by the method other than blowing into the molten iron bath surface by upper lance exceeds 20 mass% of the whole, the effect of the dephosphorization reaction promotion effect by injecting a refiner into a molten iron bath surface with gaseous oxygen tends to fall. There is this.

In addition, in order to improve the dephosphorization efficiency, it is preferable to stir the molten iron. This gas stirring is performed by blowing inert gas such as nitrogen or Ar into the molten iron through, for example, an immersion lance, a blowing nozzle immersed in the side wall or the bottom of the molten iron vessel, and the like. As a supply amount of such a stirring gas, in order to obtain sufficient bath stirring property, it is 0.02 Nm ³ / min / melting ton or more, and if the stirring of the bath is too strong, C in the molten iron reduces the generated FeO. Since the speed becomes too large, it is preferable to be 0.3 Nm ³ / min / melting tone or less.

As a molten iron container (refining vessel) for dephosphorization treatment, a converter is most preferable in that a freeboard can be sufficiently secured. For example, any vessel such as molten iron ladle or topidoca is preferable. Can be used.

Figure 3 shows an embodiment of the present invention method using a converter container, (1) is a converter container, (2) a top blowing lance, (3) a bottom blowing nozzle installed in the bottom part. In this example, the refining agent is blown into the metal bath surface using gaseous oxygen as the carrier gas from the upper blowing lance 2, and stirring gas is blown into the molten iron from the low blowing nozzle 3.

In the conventional dephosphorization treatment, adding CaF ₂ (fluorite) was essential in order to promote CaO goods, but in consideration of the recent impact of F on the environment, it is required to suppress the use of CaF ₂ even in steel refining. It is becoming. In this respect, the present method does not substantially add CaF ₂ (that is, does not add CaF ₂ other than that contained as an unavoidable impurity in the refining agent) or adds a small amount of CaF ₂ to achieve high dephosphorization efficiency. You can get it. Therefore, even when CaF ₂ is added in order to promote the goods of CaO, the amount of addition is preferably 2 kg / melting tonne or less, preferably 1 kg / melting tonne or less. In addition, as described later, in the present invention, the effect of significantly reducing the amount of slag lost after treatment can be obtained as compared with the conventional method. However, by not adding CaF ₂ or suppressing the amount of slag added in a very small amount, Since fluidity can be made lower, the said effect can be heightened more.

Usually, the P content of the molten iron before dephosphorization is 0.10% by mass or more, but in the present invention, the P content required for the crude steel, that is, the steel component specification value or less (usually 0.020% by mass or less), preferably dephosphorized to 0.010% by mass or less It is preferable to refine. As a result, in continuous converter smelting, by performing only practical decarburization and refining without substantially loading crude materials, decarburization and refining can be extremely simplified, and refining time can be shortened. It is possible to effectively reduce the amount of slag generated in the process, and (3) Since substantially no crude materials are used in the decarburization and refining process, when the manganese ore is added as a manganese source, very high Mn production can be obtained.

EMBODIMENT OF THE INVENTION Hereinafter, some preferable embodiment of the method of this invention is described. By implementing this invention method in embodiment as described below, it becomes possible to further improve the dephosphorization reaction efficiency.

In the first embodiment of the present invention, the feed rate B (kg / min / melting ton) in terms of CaO of the refining agent blown into the molten iron bath surface, and the feed rate A (Nm ³ / min /) of gaseous oxygen injected into the molten iron bath surface. The molten iron ton is dephosphorized to satisfy the following formula (1).

0.3? A / B? (One)

In addition, in order to obtain higher dephosphorization reaction efficiency, the feed rate B (kg / min / melting ton) of the CaO conversion of the refining agent blown into the molten iron bath surface, and the feed rate A (Nm ³ / It is preferable to perform dephosphorization treatment so that min / melting ton) may satisfy following formula (2).

1.2? A / B? (2)

As a result of the investigation by the present inventors, in the method of injecting gaseous oxygen and a refining agent into the molten iron bath surface, the dephosphorization reaction changes according to the supply rate of gaseous oxygen and the CaO (refining agent), specifically, gaseous oxygen FeO was generated in the molten iron bath area supplied with, but it was confirmed that a desirable feed rate of CaO was found to match the amount produced. Here, if the gas oxygen feed rate is too small in the ratio of the gas oxygen feed rate to the CaO feed rate, FeO is not generated in the molten iron bath area in which the gas oxygen is supplied. The goods (creation of CaO-FeO-based fusion) do not proceed, and CaO remains unrefined and does not act effectively on dephosphorization. On the other hand, if the feed rate of gaseous oxygen is too large, CaO necessary for dephosphorization is insufficient with respect to the oxygen supply amount, and in this case, CaO-FeO-based melts are not sufficiently produced. For this reason, in either case, the dephosphorization of the molten iron by the dephosphorization reaction mechanism described above becomes an unfavorable condition, and there is a tendency that a high dephosphorization rate cannot be obtained. In addition, when the supply rate of gaseous oxygen is too large, the amount of reactive oxygen other than oxygen necessary for dephosphorization increases, and since it is consumed in decarburization or the like, a heat source is insufficient in a later step, resulting in a significant increase in operating cost in decarburization.

Here, when the A / B is less than 0.3, the amount of CaO supplied is excessive with respect to the amount of gaseous oxygen supplied, so that FeO in an amount corresponding to the amount of CaO is not generated in the molten iron bath surface region in which gaseous oxygen is supplied. For this reason, since the supply of the CaO supplied (creation of CaO-FeO type | mold melt | fusion) does not fully advance and CaO remains unreacted and does not act effectively on dephosphorization, dephosphorization rate tends to fall. On the other hand, when A / B exceeds 7, the CaO necessary for dephosphorization is insufficient with respect to the amount of gaseous oxygen supply, and in this case, the dephosphorization rate tends to decrease because CaO-FeO-based melts are not sufficiently produced. In addition, by setting the A / B in the range of 1.2 to 2.5, the balance between the amount of FeO produced by the supply of gaseous oxygen and the amount of CaO supplied can be further optimized, and a particularly high dephosphorization reaction efficiency can be obtained.

A second embodiment of the present invention is a dephosphorization treatment performed using a ladle type or topidoca type container, and in the dephosphorization treatment using a ladle type or topidoca type refining vessel, gaseous oxygen and at least part of the dephosphorization process are carried out through a top lance. In addition to blowing the scouring agent into the molten iron bath surface, the gas containing the powder is blown into the molten iron through an immersion lance or / and blowing nozzle.

The inventors of the present invention have examined the method of performing the molten metal dehydration using the ladle type or topidoka type refining vessel more efficiently.As a result of injecting gaseous oxygen and a refining agent into the molten iron bath surface through the upper lance, It was confirmed that the method of blowing the gas containing the powder into the molten iron was very effective.

In this second embodiment, it is preferable that the amount of gaseous oxygen (conveyed amount, amount) blown into the molten iron bath surface from the upper suction lance is 0.7 Nm ³ / min / molten iron or less. If the amount of acid from the upper lance is excessive, there is a fear that slag overflow occurs from the refining vessel by slag forming. Slag forming is suppressed by setting the amount of feed from the upper lance to be 0.7 Nm ³ / min / melting ton or less, thereby enabling stable operation.

Also in this second embodiment, the refining agent may be added to the molten iron bath surface by blowing into the molten iron bath or bath, in addition to blowing into the molten iron bath surface by the upper blowing lance. It is preferable that the quantity of the refiner to make shall be 80 mass% or more of the whole refiner. If the ratio of the refiner added by blowing into the molten iron bath surface by upper lance is less than 80 mass% of the whole, there exists a tendency for the effect of the dephosphorization reaction promotion by blowing a refinery agent into a molten iron bath surface with gaseous oxygen to fall.

Figure 4 shows the relationship between the ratio of the amount of refining agent added to the total amount of refining agent and the amount of required lime based on the test results performed by the inventors. ) With a P content of 0.10 to 0.11% by mass and Si content of 0.07% by mass or less, using a gaseous oxygen (4.5 to 5.ONm ³ / melting ton) as a carrier gas, lime powder having a particle diameter of 1 mm or less as a refining agent. The dephosphorization treatment (treatment time: 15 minutes) was performed by blowing (0-6 kg / molten ton) from the upper lance to the molten iron bath surface and blowing the powder through the immersion lance. The amount of powder blown through the immersion lance was kept constant at 90 kg / min. The remainder of the necessary lime powder was used for part or all of this powder, and dust (dust, Fe content 40 mass%) or coke powder was used for the insufficient powder. In this dephosphorization treatment, CaF ₂ was not added to the refining agent, and the amount of slag after the treatment was set to 20 kg / mol ton or less. The ratio A / B between the feed rate B of lime blown into the molten iron bath surface (kg / min / melting ton) and the feed rate A of gaseous oxygen blown into the molten iron bath surface (Nm ³ / min / melting ton) was 2.0. The amount of lime added was within the range of the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined by the formulas (5) and (6) described later. In addition, the depth L (L value defined by Formula (7) mentioned later) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. On the other hand, the molten iron temperature before and after dephosphorization treatment was 1300-1320 degreeC. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag. 4 shows the amount of lime necessary for the P content in the molten iron after the treatment to be 0,02% by mass or less.

According to Fig. 4, the amount of required lime decreases as the ratio of the amount of the refinery supplied through the upper lance to the total amount of refinery is increased, and the amount of required lime is particularly reduced when the ratio is 80% by mass or more. .

There are no particular restrictions on the type of powder blown into the molten iron together with the gas, and for example, a part of the refining agent such as lime powder, a powder mainly made of carbon sources such as dust, coke powder, etc. generated in steel mills such as converter dust, etc. One kind or two or more kinds of powders such as iron oxide such as powder and mill scale, CaCO ₃ , Ca (OH) ₂ , and CaMg (CO ₃ ) ₂ can be used.

Among them, when a refining agent such as lime powder is used as the powder, the refining agent blown in the middle of the surface of the molten iron is heated to promote melting of slag when floating on the molten iron bath surface.

In addition, the use of dust generated in steel mills makes effective use of waste. That is, since dusts are powdery, in order to reuse them, it is necessary to process such as briquette in view of easy handling, but in the present embodiment, briquetization is performed. It can be reused as a powder without the effort and expense. In addition, the powder mainly composed of a carbon source becomes an effective heat source in the next step by calcining molten iron. In addition, powders such as CaCO ₃ , Ca (OH) ₂ , and CaMg (CO ₃ ) ₂ are pyrolyzed in molten iron to generate gases (CO ₂ , H ₂ 0), which contribute to agitation of the bath. At the same time, CaO generated by pyrolysis functions as a refining agent. In addition, the powder of iron oxide becomes a part of an oxygen source in a bath.

There is no particular limitation on the kind of gas (carrier gas) blown into the molten iron together with the powder, and inert gas such as gaseous oxygen (oxygen gas or oxygen-containing gas), N ₂ or Ar, and the like can be used. Among these, when the refining agent is blown in by gaseous oxygen, the effect of promoting the reaction can be expected by the so-called transient reaction when the molten iron floats. However, since oxygen gas is supplied from the immersion lance or the blowing nozzle, FeO is generated at the lance or the tip of the nozzle, and the life of the lance and the nozzle is a problem. In contrast, in the case of using an inert gas such as N ₂ or Ar, the effect on the reaction surface cannot be expected, but the life of the lance and the nozzle is longer than in the case of using gaseous oxygen. Therefore, the type of gas to be used may be selected in consideration of the total cost including the lance and the life of the nozzle.

As the means for blowing the refiner into the molten iron, a blowing nozzle provided in the immersion lance or the refining vessel, or both thereof can be used. As a blow nozzle, an arbitrary type of thing, such as a bottom blowing nozzle and a horizontal blowing nozzle, can be used.

In addition, in this 2nd Embodiment, when substantially the whole quantity of a refiner | purifier is added by blowing into the molten iron bath surface through an upper suction lance, and blowing into the molten iron through an immersion lance or / and a blowing nozzle, It is preferable to make the addition amount of the refiner | purifier through a deodorization lance 20-80 mass% of the total addition amount of a refiner | purifier. When the ratio of the refiner blown into the molten iron bath surface through the upper bleeding lance exceeds 80% by mass of the total amount of the refiner, it is difficult to obtain the stirring power required for the dephosphorization reaction because the stirring effect of the molten iron due to the blowing of the refiner into the molten iron is small. On the other hand, if it is less than 20 mass%, the above-mentioned goods promotion effect by blowing a refiner into a molten iron bath surface cannot fully be obtained.

Fig. 5 is a deodorization based on the test results performed by the inventors for the case where the entire amount of the refining agent is added by blowing into the molten iron bath surface through the upper blowing lance and blowing into the molten iron through the immersion lance or / and the blowing nozzle. The relationship between the ratio of the amount of refining agent added through the lance to the amount of refining of the refining agent and the dephosphorization efficiency is shown. In this test, the P content in the ladle-type container (150 tons): 0.10 to 0.11 mass% and the Si content: 0.07 mass% For the following molten iron, lime gas (0 to ⁶ kg / melting ton) having a particle diameter of 1 mm or less, which is a refining agent, is blown into the molten iron bath surface using gaseous oxygen (4.5 to 5.ONm ³ / molten ton) as a carrier gas. The dephosphorization treatment (treatment time: 15 minutes) was performed by blowing the rest of the required lime powder (0 to 6 kg / melting ton) through the immersion lance. In this dephosphorization treatment, CaF ₂ was not added to the refining agent, and the amount of slag after the treatment was set to 20 kg / mol ton or less. The ratio A / B between the feed rate B of lime blown into the molten iron bath surface (kg / min / melting ton) and the feed rate A of gaseous oxygen blown into the molten iron bath surface (Nm ³ / min / melting ton) was 2.0. The amount of lime added was within the range of the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined by the formulas (5) and (6) described later. In addition, the depth L (L value defined by Formula (7) mentioned later) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. On the other hand, the molten iron temperature before and after dephosphorization treatment was 1300-1320 degreeC. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag.

According to Fig. 5, the dephosphorization efficiency is greatly reduced in the region where the ratio of the amount of refinery addition added to the refinery addition amount through the upper lance is less than 20% by mass and more than 80% by mass.

Fig. 6 shows an example in which the present embodiment is applied when the molten iron dephosphorization treatment is performed in the blast furnace ladle dephosphorization equipment. Depending on the Si content in the molten iron drawn out from the blast furnace, if necessary, degreasing treatment such as columnar degreasing is performed before dephosphorization. In the dephosphorization treatment, molten iron is poured into the blast furnace 4, the lime powder (refining agent) is injected from the lance 5 immersed in the molten iron, and the lime powder (refining agent) is melted together with gaseous oxygen from the upper lance 2. Blow into sleep. At this time, the supply rate of the lime powder to be sprayed is such that the molten iron is sufficiently stirred.

In the third embodiment of the present invention, the dephosphorization treatment is performed so that the supply rate of the refiner injected into the molten iron bath surface and the supply rate of gaseous oxygen satisfy the conditions of the following formulas (3) and (4).

(C1 / D1)> (C2 / D2)... (3)

C1> C2... (4)

However, C1: Average value of refining agent supply rate in terms of CaO in the dephosphorization treatment (kg / min / melting ton)

   C2: Average value of refining agent feed rate in terms of CaO in the latter stage of dephosphorization (kg / min / melting ton)

D1: Average value of gaseous oxygen feed rate in dephosphorization (Nm ³ / min / melting ton)

D2: Average value of gaseous oxygen supply rate in the late dephosphorization treatment (Nm ³ / min / melting ton)

Since the dephosphorization treatment has a high P content in the molten iron, the greater the dephosphorization rate is, the higher the P content in the molten iron becomes. The P content of is lowered, so that the movement of [P] in the metal of the reaction site is at a rate, so that the proportion of the refining agent which contributes more effectively to the dephosphorization effect than the dephosphorization treatment is reduced. Therefore, the supply rate ratio (refining agent supply rate / gas oxygen supply rate) of the refiner and gaseous oxygen supplied to the molten iron bath surface in the specific form as described above, and the supply rate of the refining agent are reduced in the latter stage of dephosphorization treatment for the first time of dephosphorization treatment. As a result, an efficient dephosphorization treatment can be performed at a smaller amount of refiner addition.

In the method of the present invention, the reactivity of the refining agent can be effectively increased for the reasons described above, so that the effective dephosphorization treatment can be performed while adding the minimum necessary refining agent in the latter stage of the dephosphorization treatment.

FIG. 7 shows that in a converter-type dephosphorization refining furnace (300 tons), without adding CaF ₂ , dephosphorization treatment is carried out under the conditions (1) and (2) below so that the P content in the molten iron after dephosphorization treatment is 0.012% by mass. The relationship between CaO raw unit and dephosphorization efficiency is investigated.

① The feed rate C (kg / min / melting ton) of the refiner injected into the molten iron bath surface is made constant throughout the treatment period, and the feed rate C of the refiner and the feed rate D of gaseous oxygen D (Nm ³ / The dephosphorization process was performed by making the ratio C / D to min / molton) constant throughout the process.

② C1: Average value of refining agent supply rate in terms of CaO conversion (kg / min / melting ton) in the preceding dephosphorization treatment, C2: Average value of refining agent supply rate in terms of CaO conversion in the late dephosphorization treatment (kg / min / melting chart) ton), D1: mean value of gaseous oxygen supply rate (Nm ³ / min / molten iron ton) in the dephosphorization treatment electricity, D2: mean value of gaseous oxygen supply rate in the late dephosphorization treatment (Nm ³ / min / melt ton) In this case, dephosphorization treatment was performed under the conditions of (C1 / D1)> (C2 / D2) and C1> C2.

Meanwhile, the dephosphorization efficiency η _cao is defined by the following equation as the removal of the deionized gyubun and 2CaO SiO _2,.

η _cao = [{([% P] _i -[% P] _f ) / (31 × 2)} × 56 × 3 × 10] / [W _cao -{([% Si] _i -[% Si] _f ) / 28} × 56 × 2 × 10]

However, W _cao : CaO raw material cost (kg / molton)

[% P] _i : P content (mass%) in molten iron | metal before dephosphorization treatment

[% P] _f : P content (mass%) in molten iron after dephosphorization treatment

[% Si] _i : Si content (mass%) in molten iron | metal before dephosphorization treatment

[% Si] _f : Si content (mass%) in molten iron after dephosphorization treatment

In this test, the blast furnace molten iron was degreased in columnar and molten iron ladle as needed, and then desulfurized in molten iron ladle, and the molten iron was transferred to a converter type container for dephosphorization treatment. P content in the molten iron | metal before dephosphorization was 0.10 to 0.11 mass%, and Si content was 0.07 mass% or less. As the refining agent, only calcined lime of CaO principal without CaF ₂ was used. In addition, gaseous oxygen was mainly used as an oxygen source, and this was added by blowing into a molten iron bath surface from a top lance, and the addition of the solid acid source (iron ore) was used together for some. The refining feed amount was set to 4.6-9.0 kg / melting ton, and the gaseous oxygen supply amount was set to 8.6-13.6 Nm ³ / melting ton. Further, ① for the dephosphorization process, C / D were 0.50~0.69kg / Nm ³ a. In the dephosphorization treatment of ②, C1 is 0.88 to 1.00 kg / min / melting ton, C2 is 0.30 to 0.39 kg / min / melting ton, C1 / D1 is 0.60 to 0.83 kg / Nm ³ , and C2 / D2 is 0.38 to 0.48. It set to kg / Nm <^3> and set it to (C1 / Dl) * 56-72% = (C2 / D2). In addition, the amount of slag after processing was made into 20 kg / molten iron or less. The amount of lime added was within the range of the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined by the formulas (5) and (6) described later. In addition, the depth L (L value defined by Formula (7) mentioned later) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. On the other hand, the molten iron temperature before and after dephosphorization treatment was 1300-1320 degreeC. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag.

According to FIG. 7, it turns out that in the dephosphorization process of (2), compared with the case of (1), CaO unit is small and dephosphorization efficiency is high. This is because in the case of (2), sufficient dephosphorization was performed without adding extra refining agent in the later stage of refining, and thus high dephosphorization efficiency was obtained.

In this third embodiment, the desired effects can be obtained by setting the refining agent feed rate and the gaseous oxygen feed rate to (C1 / D1)> (C2 / D2) and C1> C2, but in particular, these are (C1 / D1). It is preferable to set it as the range of (x) x30 to 80% = (C2 / D2) and C1x30 to 80% = C2. At (C1 / D1) × 30%> (C2 / D2) and Cl × 30%> C2, the dephosphorization rate tends to decrease because the supply amount of the refining agent is insufficient, while (C1 / D1) × 80% < In (C2 / D2) and C1 x 80% <C2, since the excess amount of refining agent supplied in the late dephosphorization treatment increases, the dephosphorization efficiency tends to decrease.

In this third embodiment, the refining agent and the gaseous oxygen may be supplied in accordance with the above conditions during the dephosphorization treatment period (previous and late stage of the dephosphorization treatment). Therefore, the form of changing the refining agent supply rate and gaseous oxygen supply rate is It is optional and can be changed continuously or stepwise or both.

In the fourth embodiment of the present invention, the molten iron having a Si content of 0.15% by mass or less is blown off with a gaseous oxygen and at least a part of a refining agent into the molten iron bath surface through a top lance, and the dephosphorization treatment is carried out. In the refining agent, the total amount of lime W _cao _P (kg / melting ton) obtained by the following formula (5) and the amount of lime W _cao _Si (kg / melting ton) obtained by the following formula (6) are added. Lime is added.

W _cao _P = (melting line [P]-target [P]) x (10/62) x 56 x 3 / η _cao . (5)

However, molten iron [P]: P content in molten iron before dephosphorization (mass%)

    Target [P]: P content (mass%) in molten iron | metal after target dephosphorization treatment.

η _cao (lime efficiency) = 0.5 to 1

W _cao _Si = molten iron [Si] x (10/28) x 56 x 2. (6)

However, molten iron [Si]: Si content (mass%) in molten iron before dephosphorization treatment

As described above, in the conventional dephosphorization treatment, a slag volume is determined in response to phosphorus distribution Lp on the premise of maintaining the slag in a uniform liquid state. The amount of refining agent required was greater than the amount of refining necessary to fix it. In the present invention, on the other hand, the present invention employs a mechanism called direct dephosphorization reaction in the molten iron bathing area centered on a hot spot and the fixation of P by slag of a solid main body in the outer region. The minimum required amount of refining agent, such as dephosphorization reaction can be efficiently generated.

In fact, the amount of lime consumed to fix P and Si in the molten iron can be calculated by the following equation. In the following equation, W _cao _P _0, the lime amount (kg / hot metal ton) to be consumed in order to secure the P in the hot metal, W _cao _Si _0, the lime amount to be consumed in order to hold the Si in the molten iron ( kg per ton.

W _cao P ₀ = (melting line [P]-target [P]) × (10/62) × 56 × 3

However, molten iron [P]: P content (mass%) in molten iron before dephosphorization treatment

    Target [P]: P content (mass%) in molten iron | metal after target dephosphorization treatment.

W _cao Si ₀ = molten iron [Si] × (10/28) × 56 × 2

However, molten iron [Si]: Si content (mass%) in molten iron before dephosphorization treatment

Here, when the total amount of lime added is Total CaO (kg / melting ton), the efficiency η _cao of the lime contributed to dephosphorization can be calculated as shown in the following formula.

η _cao = W _cao _P ₀ / (Tota1 CaO-W _cao _Si ₀ )

In this embodiment, first, this lime efficiency (eta) _cao was prescribed | regulated to 0.5-1. The lower limit of η _cao is defined from the viewpoint of not causing useless lime addition and appropriately generating a dephosphorization reaction for the purpose of the present invention. In other words, when η _cao is less than 0.5, practically useless lime addition is carried out, and the effect of the present invention that the effective dephosphorization treatment is performed with a small amount of refining agent is lost, and a predetermined oxygen source unit is used. Since the addition amount of lime becomes excessive with respect to FeO produced | generated in the following, CaO which cannot be rehydrated exists in a large quantity, and such non-reactable CaO inhibits the progress of the dephosphorization reaction mentioned above.

In this embodiment, to 5 lime amount to be calculated by the formula W _cao _P (kg / hot metal ton) and to 6 lime amount to be calculated by the formula W _cao _Si total amounts of the (kg / hot metal ton) Lime is added to dephosphorization treatment.

W _cao _P = (melting line [P]-target [P]) x (10/62) x 56 x 3 / η _cao . (5)

However, molten iron [P]: P content (mass%) in molten iron before dephosphorization treatment

    Target [P]: P content (mass%) in molten iron | metal after target dephosphorization treatment.

η _cao (lime efficiency) = 0.5 to 1

W _cao _Si = molten iron [Si] x (10/28) x 56 x 2. (6)

However, molten iron [Si]: Si content (mass%) in molten iron before dephosphorization treatment

W _cao _P is the amount of lime required to fix P in molten iron as 3CaO.P ₂ 0 ₅ when η _cao = 0.5 to 1, and W _cao _Si is Si in the molten iron. Is the amount of lime required to fix as 2CaOSiO ₂ .

FIG. 8 shows, as an example, the amount of lime added in response to the Si content in the molten iron in the present embodiment, in the case where the molten iron having a P content of 0.11% by mass is dephosphorized to a P content of 0.015% by mass. It is shown in comparison with the amount of lime added in the dephosphorization treatment, W _cao _Si is the amount of lime necessary for fixing Si, and W _cao _P ₁ is necessary for fixing P (de-P) in the case of η _cao = 1. lime amount, W _cao _P _0.5 is the case of η = 0.5 _cao lime amount required for the fixing of the stand P, W is the amount of lime to be added in the conventional method. As shown in the figure, since the amount of lime required in the conventional method is determined by the phosphorus distribution Lp and the required slag amount, the amount of lime in W is required regardless of the Si concentration in the molten iron. In the embodiment, the amount of lime added is sufficient as [W _cao _Si + W _cao _P ₁ ] to [W _cao _Si + W _cao _P _0.5 ], and the amount of lime added can be greatly reduced as compared with the conventional method.

9 shows the necessary lime amount for de-P and lime efficiency η _cao in the present embodiment and the conventional method in relation to the P content in molten iron after dephosphorization treatment. The required lime amount of the dragon indicates [Ｗ-W _cao _Si] in FIG. 8. According to FIG. 9, it turns out that this embodiment performs dephosphorization treatment with high lime efficiency using very little deliming lime compared with the conventional method.

In this embodiment of the claim 4, it is preferred that at least 80% by weight of lime in the lime amount W _cao _P (η _cao = 1 W _cao _P, or less equal to that obtained in) to blow the hot metal bath surface through the sangchwi lances . 10 is the relationship between the lime amount inventors conducted blown, the molten iron bath surface from sangchwi lance based on the test result X and the lime amount W _cao _P with non-X / W _cao _P and dephosphorization processing molten iron of the P content after In this test, gaseous oxygen (10-15 Nm ³ / melting ton) was applied to molten iron having a P content of 0.095 to 0.135% by mass and a Si content of 0.02 to 0.10% by mass in the converter-type container (340 tons). ) As a carrier gas and dephosphorization treatment (treatment time: 10-14 minutes) by blowing lime powder (4-10 kg / melting ton) having a particle diameter of 1 mm or less into the molten iron bath surface from the upper suction lance, and then turning the molten iron into a decarburization converter. It was charged in and decarburized. In the dephosphorization treatment, the CaF ₂ addition amount was 1 kg / melting tonne or less, and the slag amount after treatment was 30 kg / melting tonne or less. The ratio A / B between the feed rate B of lime blown into the molten iron bath surface (kg / min / melting ton) and the feed rate A of gaseous oxygen injected into the molten iron bath surface (Nm ³ / min / melting ton) was 1.7. Moreover, the depth L (L value defined by Formula (7) mentioned later) formed in the molten iron bath surface by blowing the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. In addition, the molten iron temperature before and after dephosphorization treatment was 1300-1320 degreeC. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag.

According to FIG. 10, when the ratio of the said amount of lime X in lime amount W _{cao_P} becomes less than 80 mass%, there exists a tendency for the dephosphorization rate to fall slightly. This is considered to be because it is relatively difficult to obtain a high reaction efficiency as described above by directly injecting a refining agent into a hot spot serving as a reaction site or a gaseous oxygen supply region in the vicinity thereof.

Since Si is more likely to burn than C or Fe, it can be stably present as SiO ₂ in molten iron during blowing, and therefore it is not necessary to react with lime in hot spots. Therefore, the lime member corresponding to the amount of lime W _cao _Si for fixing the generated SiO ₂ is not limited to slaked lime, but may be a material containing unreacted lime. Therefore, as the refining agent corresponding to the amount of lime W _cao _Si, one or more kinds selected from a steel slag containing lime powder, calcined lime, calcareous lime and unreacted CaO can be used. As the steel slag, for example, converter slag generated in the decarburization process (basicity of about 3 to 4), ladle slag, or the like can also be used.

In this fourth embodiment, the Si content of the molten iron to be dephosphorized is 0.15% by mass or less, and preferably 0.07% by mass, in order to obtain a high dephosphorization efficiency for the reason described above and with a small amount of refiner addition. Hereinafter, More preferably, you may be 0.03 mass% or less. When Si content of a molten iron exceeds 0.1 mass%, the effect of reducing the addition amount of the refiner | purifier in this embodiment becomes small.

In the fifth embodiment of the present invention, it is defined by the following formula (7). The depth L of the concave portion formed in the molten iron bath surface by blowing of gaseous oxygen or blowing of a gaseous oxygen as a carrier gas is set to 200 to 500 mm. To control.

L = L ₀ × exp {(-0.78 × L _H ) / L ₀ } … (7)

L ₀ = 63 × {(F ₀₂ / n) / d _t } ^2/3

However, L _H : Lance height of upper lance (mm)

F ₀₂ ： Gas oxygen supply rate from upper lance (Nm ³ / hr)

    n: Nozzle Air Lift

d _t : Nozzle bore diameter (mm) of uptake lance (However, if the nozzle diameter of a plurality of nozzle holes is different, average nozzle diameter of all nozzle holes)

In order to obtain a high dephosphorization efficiency with a small refiner addition amount by the dephosphorization reaction target which this invention aims at, in particular, the method of supplying gaseous oxygen to the hot spot which is a reaction site, specifically, gaseous oxygen or gas It has been found that it is desirable to control the depth of the recesses (theoretical recess depth calculated from the gas oxygen supply rate and the composition of the upper lance and the conditions of use) by the injection of oxygen and the refining agent in the optimum range.

Here, if the depth of the recess formed in the molten iron bath surface by the gaseous oxygen or the gaseous oxygen and the refining agent is too small, that is, when the gaseous oxygen or the gaseous oxygen and the refining agent is too weak, the slag is formed outside the hot spot. This occurs and the foamed slag obstructs the flow of the gaseous oxygen jet, so that the supply of gaseous oxygen to the hot spot is lowered, which is a disadvantageous condition for improving the dephosphorization efficiency. In addition, since the supply of oxygen to the hot spot becomes unstable, oxygen necessary for dephosphorization is not stably supplied, the variation in dephosphorization efficiency increases, and 3CaO · P ₂ 0 ₅ decomposes, and It occurs.

On the other hand, if the depth of the concave portion formed in the molten iron bath surface by the gaseous oxygen or the gaseous oxygen and the refining agent is too large, that is, when the gaseous oxygen or the gaseous oxygen and the refining agent is too strong, the oxygen density in the hot spot becomes excessively high. P corresponding to FeO to be made is not sufficiently supplied from the metal. As a result, decarburization advances with the excess amount of FeO, and this case also becomes an unfavorable condition for improving the dephosphorization efficiency.

The depth L of the recessed portion formed in the molten iron bath surface by blowing of gaseous oxygen or blowing of a refining agent containing gaseous oxygen as a carrier gas can be defined by the following formula (7).

L = L ₀ × exp {(-0.78 × L _H ) / L ₀ }... (7)

L ₀ = 63 × {(F ₀₂ / n) / d _t } ^2/3

However, L _H : Lance height of upper lance (mm)

F ₀₂ : Gas Oxygen Supply Rate from Upper Lance (Nm ³ / hr)

    n: Nozzle Air Lift

d _t : Nozzle bore diameter (mm) of uptake lance (However, if the nozzle diameter of a plurality of nozzle holes is different, average nozzle diameter of all nozzle holes)

In this embodiment, the depth L of the said recessed part in a molten metal bath surface is controlled to 200-500 mm, and dephosphorization process is performed. Fig. 11 shows the relationship between the depth L of the recessed portion of the molten iron bath surface and the P content in the molten iron after dephosphorization treatment based on the test results performed by the present inventors. With respect to molten iron having a P content of 0.195 mass% and a Si content of 0.02 mass% to 0.15 mass%, lime powder having a particle diameter of 1 mm or less, which is a refining agent, is made of gaseous oxygen (10 to ¹⁵ Nm ³ / melting ton) as a carrier gas. After dephosphorization treatment (treatment time: 10-14 minutes) by blowing 4-10 kg / melting ton from the upper lance to the molten iron bath surface, the molten iron is charged into a decarburization converter and decarburization is carried out. It is done. In this dephosphorization treatment, the CaF ₂ addition amount was 1 kg / melting tonne or less, and the slag amount after treatment was 30 kg / melting tonne or less. The ratio A / B between the feed rate B of lime blown into the molten iron bath surface (kg / min / melting ton) and the feed rate A of gaseous oxygen injected into the molten iron bath surface (Nm ³ / min / melting ton) was 1.7. The amount of lime added was within the range of the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined by the formulas (5) and (6). On the other hand, the molten iron temperature before and after dephosphorization treatment was 1300-1320 degreeC. The amount of slag after the treatment was calculated from the mass balance of CaO concentration of the added lime and the slag analysis value.

According to Figs. 11 (a) and 11 (b), in the range of less than 200 mm and more than 500 mm, the dephosphorization efficiency is lowered for the reasons described above, compared to the range of 200 to 500 mm, and the molten iron after the treatment P content tends to increase.

In the sixth embodiment of the present invention, the content of CaF ₂ is set to 1 kg / molten ton with respect to molten iron having a Si content of 0.15% by mass or less, preferably 0.07% by mass or less, and more preferably 0.03% by mass or less. The gaseous oxygen and at least a part of the refiner are blown into the molten iron bath through a odor lance under the condition that substantially no CaF ₂ is added (ie, no CaF ₂ other than that contained as an unavoidable impurity in the refiner). By performing the dephosphorization treatment, the molten iron temperature at the end of the dephosphorization treatment is set to 1360 ° C to 1450 ° C.

Since the dephosphorization reaction is an oxidation reaction of P, conventionally, it has become common knowledge that the melting temperature is advantageous at a lower temperature, and in the related art, it is thought that the treatment of slag to metal is generated when the treatment is performed at a high melting temperature. there was. For this reason, it has conventionally been thought that it is difficult to lower P content in molten iron | metal to a low level even if it carries out dephosphorization treatment in the high temperature area of 1360 degreeC or more. On the other hand, the inventors of the present invention, if the content of Si in the molten iron to be dephosphorized in the present invention method is sufficiently low, and the dephosphorization treatment is carried out under the condition that the content of CaF ₂ is low or no addition, from the slag to the metal even if the high temperature treatment is performed. It was confirmed that there is almost no compound of, and high dephosphorization reaction efficiency can be obtained. Thus, even if the high temperature treatment is performed, the compounding speed can be reduced because the refiner is supplied to the molten iron bath area in which a large amount of FeO is generated by gaseous oxygen, and thus, CaO is added to the loading method of calcareous ash. The area where the (refining agent) comes into contact with FeO is significantly larger, which increases the efficiency and speed at which P ₂ 0 ₅ oxidized with FeO reacts with CaO, thereby shortening the melting time of the CaO-FeO melt. I think it is. In short, it is thought that the dephosphorization reaction can be completed in a very short time and the subsequent melting time of the slag is short, so that the compounding speed can also be reduced.

12 is a dephosphorization treatment of molten iron under the condition that CaF ₂ is not added in the converter-type container 300ton, and the molten iron temperature (melting temperature at the end of the dephosphorization treatment) and the dephosphorization treatment before dephosphorization treatment The effect of Si content in molten iron is compared. On the other hand, also referred to as dephosphorization lime efficiency shown in Fig. 12 also has a ratio of lime contributed to the dephosphorization of the former lime (calcium hydroxide) was added as a refiner, phosphate is stoichiometric with the assumption that fixed as 3CaO and P ₂ 0 ₅ It is derived from rain.

In this test, the blast furnace molten iron was degreased in the columnar and the molten ladle as needed, and then desulfurized in the molten iron ladle, and the molten iron was transferred to a converter type vessel for dephosphorization. Si content and the molten iron temperature after treatment were varied. P content of molten iron before dephosphorization was 0.10 to 0.11 mass%, Si content was 0.15 mass% or less, and P content in molten iron was 0.02 mass% or less by dephosphorization treatment.

As the refining agent, only calcined lime of CaO principal without CaF ₂ was used. In addition, gaseous oxygen was mainly used as an oxygen source, and this was added by blowing into a molten iron bath surface from a top lance, and the addition of the solid acid source (iron ore) was used together for some. The deoxygenated oxygen content was controlled in the range of 10 to ¹¹ Nm ³ / melt ton. The dephosphorization treatment time was 10 to 11 minutes, the molten iron temperature before scraping treatment and the amount of scrap addition were adjusted, and the molten iron temperature after dephosphorization treatment was controlled. The slag amount after the treatment was 30 kg / molten tonne or less.

In Fig. 12, ○ shows the addition of lime by the loading of the lettuce and the test example (a) in which the molten iron temperature at the end of the dephosphorization treatment was 1260-1350 ° C, and ▲ the lime (lime powder having a particle diameter of 1 mm or less). It is the test example (b) which blows oxygen into a molten iron bath surface using a carrier gas, and sets molten iron temperature at the time of completion | finish of dephosphorization treatment to 1360-1450 degreeC. The amount of lime added was changed in the range of 5 to 10 kg / melting ton depending on the Si content in the molten iron. In Test Example (b), the ratio A between the feed rate B of lime blown into the molten iron bath surface (kg / min / melting ton) and the feed rate A of gaseous oxygen injected into the molten iron bath surface (Nm ³ / min / melting ton) / B is 1.7, and the amount of lime added is the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined in the above formulas (5) and (6). It was made into the total range. In addition, the depth L (L value defined by Formula (7) mentioned above) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. The amount of slag after the treatment was calculated from the mass balance of CaO concentration of the added lime and the slag analysis value.

According to FIG. 12, regardless of the lime supply method or the molten iron temperature at the end of the dephosphorization treatment, the lower the Si content in the molten iron is, the lower the CaO consumption rate is due to 2CaOSiO ₂ . , When lime is added to the molten iron bath with gaseous oxygen as compared to the case where the molten iron temperature at the end of dephosphorization treatment is 1260-1350 ° C. (Test Example (a)) by adding lime by means of the loading of lettuce. When the molten iron temperature at the time of completion | finish was 1360-1450 degreeC (test example (b)), the demineralization efficiency improved. This effect is more remarkable as the content of Si in the molten iron decreases. On the average, the dephosphorization reaction is advantageously at a lower temperature. However, the result of FIG. 12 is considered to be because, in the test example (b), the ablation rate was reduced due to slag melting and immobilization of the dephosphorization product.

FIG. 13 illustrates the effect of CaF ₂ addition on the dephosphorization efficiency (demineralization efficiency) in the method of blowing the refiner into the molten iron bath surface together with gaseous oxygen, using a converter container as in the test of FIG. 12. , Addition type, addition amount, treatment time and the like of the refining agent and the oxygen source were the same as in Example (b) of FIG. 13. The molten iron temperature at the end of the dephosphorization treatment was in the range of 1360 to 1450 ° C. On the other hand, CaF ₂ was added all at once at the beginning of blown-in by the loading of lettuce. The slag amount after the treatment was 30 kg / molten tonne or less.

According to FIG. 13, when the amount of CaF ₂ added is 1 kg / molton or less, dephosphorization efficiency is improved. CaF ₂ has a function of promoting the melting of CaO, and the liquidus rate of slag increases by adding CaF ₂ . However, in the case where the treatment temperature (melting temperature) is 1360 ° C or higher, when CaF ₂ is added to increase the liquid phase rate of the slag, the recovery rate from the slag to the metal increases, so that the deliming lime efficiency deteriorates easily. I think it is. Thus, to the treatment temperature (temperature of molten iron) to improve the dephosphorization efficiency as more than 1360 ℃ is, the amount of CaF _2, it is necessary to minimize (1kg / ton molten iron less than or substantially additive-free).

When the molten iron temperature at the end of the dephosphorization treatment exceeds 1450 ° C, the effect of increasing the P concentration value in the molten iron which is in equilibrium with the slag is greater than the effect of melting the CaO with the molten iron at a high temperature. For this reason, the molten iron temperature at the end of dephosphorization treatment needs to be 1450 degrees C or less.

From the above results, the amount of CaF ₂ added is 1 kg / melting ton or CaF ₂ substantially in a molten iron having a Si content of 0.15% by mass or less, preferably 0.07% by mass or less, particularly preferably 0.03% by mass or less. By carrying out dephosphorization on the conditions which do not add, it turns out that dephosphorization treatment can be performed with high dephosphorization efficiency even if the molten iron temperature at the end of dephosphorization treatment is 1360-1450 degreeC high temperature.

As described above, in the present embodiment, since the high molten iron temperature can be ensured at the end of the dephosphorization treatment, the heat margin in the subsequent step can be sufficiently secured. In addition, since the molten iron temperature after the treatment is high, the T.Fe in the slag can be suppressed low, and the dephosphorized iron production is also improved.

Generally, the molten iron temperature before dephosphorization is about 1250 to 1350 ° C. However, as a method of adjusting the molten iron temperature at the end of dephosphorization treatment, in the case of dephosphorization using a converter-type dephosphorization refinery for dissolving scraps, the amount of scrap input The method of suppressing this is mentioned. Moreover, in the case of dephosphorization treatment using ladle-type containers, such as molten iron ladle, and topidoka, the method of adjusting the input amount of solid oxygen sources, such as a sintered powder, etc. are mentioned. Therefore, the molten iron temperature at the end of the treatment may be adjusted in the range of 1360 to 1450 ° C in such a manner.

As a specific control method of the molten iron temperature at the end of the dephosphorization treatment, the molten iron temperature during the dephosphorization treatment is calculated from the gas composition analysis value and the exhaust gas temperature generated by the dephosphorization treatment, and the method of controlling the molten iron temperature based on this is the easiest. Do. That is, in this method, the exhaust gas is analyzed for gas composition to obtain CO and CO ₂ concentrations, and the amount of gas produced is calculated from the exhaust gas temperature. From these, the calorific value in the furnace can be calculated, and the molten iron temperature can be calculated based on this.

In the seventh embodiment of the present invention, a substance that absorbs heat of molten iron by chemical reaction and / or pyrolysis reaction is supplied to the molten iron bath surface region to which gaseous oxygen is supplied.

The molten iron bath surface area in which gaseous oxygen is blown is a very advantageous condition for promoting the refining of the refiner because a large amount of iron oxide is produced by the gaseous oxygen impinging on the bath surface. On the other hand, high temperature fields are formed in the bathing area (especially hot spots) where gaseous oxygen collides by an oxidation reaction, and this hot field generation is advantageous in terms of melting lime, but it is dephosphorus equilibrium. In view of the disadvantages will work.

With respect to such a problem, the present inventors have examined the measures that can make the molten iron bath area supplied with gaseous oxygen a temperature condition favorable for dephosphorization reaction, and as a result, the chemical reaction is carried out in the molten iron bath area supplied with gaseous oxygen. Or / and by supplying a material that absorbs heat of the molten iron by the pyrolysis reaction, it is possible to appropriately suppress the temperature rise in the molten iron bath area to which gaseous oxygen is supplied without inhibiting the regeneration of the refining agent by gaseous oxygen. It was found that higher dephosphorization reaction efficiency can be obtained.

The addition (supply) to the molten iron bath surface of a substance that absorbs the heat of the molten iron by chemical reaction and / or pyrolysis reaction (hereinafter referred to as the "heat absorbing substance") is the molten iron by the heat generated by the gas oxygen supplied to the molten iron bath surface In order to suppress an excessive rise in temperature, it is necessary to supply the endothermic substance to the molten iron bath surface area | region to which gaseous oxygen was supplied. Moreover, it is preferable to supply to the area | region called the "hot spot" which arises in a molten metal bath especially in the molten metal bath surface area | region to which gaseous oxygen is supplied. This is the molten iron bath surface area which becomes the highest temperature by which the oxidation reaction by the gaseous oxygen (the reaction of FeO formation) is concentrated and the area is stirred by the gaseous oxygen gas jet, so the effect by the addition of endothermic material is most remarkable. I can say that it is an area that can be obtained easily.

Here, the endothermic material is not particularly limited as long as it is a substance that deprives the heat of the molten iron by chemical reaction or thermal decomposition reaction when the molten iron is added to the molten iron, or both reactions thereof. Therefore, this endothermic substance may be either gas or solid.

As the base which can be used as a heat absorbing material, for example, there may be mentioned carbon dioxide, water vapor, nitrogen oxides (NO _x), etc., may be used those of one or more thereof. These gas endothermic substances react with Fe mainly by being supplied to the molten iron bath surface (for example, CO ₂ + Fe → FeO + CO, H ₂ 0 + Fe → FeO + H ₂ ), and at that time, Do it. As a result, for the heat generation by Fe oxidation (Fe + 1/20 _2- &gt; FeO) by gaseous oxygen, the heat is absorbed or the amount of heat generated is greatly reduced. Among the gas endothermic substances, carbon dioxide and water vapor generated in a large amount in the steel mill are particularly suitable because they are easily available and have a large thermal effect. In addition, even if the purity is somewhat low due to the incorporation of nitrogen or the like into these gases, the dephosphorization treatment is not a problem since it is not the final steelmaking step. In addition, CO and H ₂ generated by reducing the supplied carbon dioxide and water vapor are recovered as a part of the exhaust gas during the dephosphorization treatment, which also has the effect of improving the exhaust gas calories.

Moreover, as a solid which can be used as an endothermic substance, metal carbonate, metal hydroxide, Especially preferably, alkali metal, alkaline earth metal carbonate, hydroxide can be mentioned, One or more of these can be used. These solid endothermic substances mainly produce thermal decomposition reactions by being supplied to the molten iron bath surface, and at the same time endotherm the molten iron, and generate CO ₂ or H ₂ 0 by thermal decomposition, and this CO ₂ or H ₂ Since 0 functions further as an endothermic substance as mentioned above, especially a high endothermic effect can be obtained. The Examples of such metal _{carbonate, CaCO 3, CaMg (CO 3} ) 2, MgCO 3, NaCO 3, FeCO 3, MnCO 3, NaHCO 3 and the like (sodium hydrogen carbonate), and as the hydroxide of the metal Ca (OH ) ₂ , Mg (OH) ₂ , Ba (OH) ₂ , A1 (OH) ₃ , Fe (OH) ₂ , Mn (OH) _n , Ni (OH) _n , and the like. Can be used.

Among these solid endothermic substances, CaCO ₃ , Ca (OH) ₂ and CaMg (CO ₃ ) ₂ are not only easily available, but also CaO is formed by the thermal decomposition, and this CaO functions as a refining agent. It is especially preferable because there is an advantage. Usually, these solid endothermic materials are added in the form of unbaked or semi-baked limestone, dolomite.

The solid endothermic material is preferably a powder having an average particle diameter of 5 mm or less because thermal decomposition does not proceed rapidly if its particle size is too large.

The gas endothermic substance mentioned above and a solid endothermic substance may be used together, and a gas endothermic substance may be used as a part or all part of the carrier gas at the time of supplying a solid endothermic substance to a molten iron bath surface.

There is no particular limitation on the method of adding the endothermic substance (gas or / and solid), and the injection into the molten iron bath surface by the upper lance or other lance, the filling of the moistener (the charge using a shooter in the case of the solid endothermic substance), etc. The endothermic substance may be added to the molten iron bath surface to which gaseous oxygen is supplied (especially "hot spot") to reliably supply the endothermic material. It is preferable to supply to a molten iron bath surface especially by a fresh lance.

In addition, in the case of supplying the endothermic material to the molten iron bath surface by the upper lance, (1) the endothermic material is mixed with gaseous oxygen (in the case of the solid endothermic material, gaseous oxygen is used as the carrier gas) and supplied from the same lance to the molten iron bath surface. Method 2) A method of supplying endothermic material and gaseous oxygen into a lance through separate gas supply lines, and supplying them to the molten iron bath surface from separate lances. Carrier gas may be used).

The method of ① is more preferable from the viewpoint of reliably supplying the endothermic material to the molten iron bath surface area to which gaseous oxygen is supplied, but the method of ② also uses the other end of the endothermic material supplied through a predetermined lance hole. The gas can be supplied to the molten iron bath surface area supplied with oxygen. Specifically, for example, the gas endothermic material is supplied from the central lance hole at the top of the upper lance, or the endothermic material is supplied using a gas other than gaseous oxygen as a carrier gas, and the gas is supplied from another lance hole around the central lance hole. The form of supplying oxygen is preferable. An inert gas such as N ₂ or Ar is suitable as the carrier gas, and as described later, a gas endothermic material (for example, CO ₂ ) may be used as the carrier gas.

In the method of ① above, gaseous oxygen obtained by mixing only gaseous oxygen from some of the lances and endothermic material (and, in some cases, a refining agent) from the other lances, is applied to the molten iron bath surface. You can also supply.

Further, in any of the above methods (1) and (2), the refining agent may be supplied to the molten iron bath surface alone or in combination with the endothermic material (gas or / and solid) to a carrier gas or a gas endothermic material other than gaseous oxygen or gaseous oxygen. It may be.

In order to supply the endothermic material (gas or / and solid) or the endothermic material and the refining agent with gaseous oxygen to the molten iron bath through the upper lance, for example, the oxygen supply line (header, piping, lance of the upper lance) The endothermic material may be supplied to a part or all of the gaseous oxygen flow paths inside) and mixed with gaseous oxygen.

The endothermic material (gas or / and solid), or the endothermic material and the refining agent may be supplied to the molten iron bath surface using a supply means other than the upper lance (for example, another lance). The lances other than the upper lance may be ones capable of supplying a powder to a predetermined position in the furnace like the upper lance, and are usually used in sub-lances used for sampling, temperature measurement, or the like. sub-lances and the like can also be used if there is no problem with the cooling capacity in the furnace. In addition, even if the device is an injection device such as a shooter or an injection device, it may be used as long as there is no problem in the solvent resistance at high temperature or the accuracy of the injection position.

Further, as described above, the refiner is blown (projected) into the molten bath surface area (particularly, the region of the "hot spot" mentioned above) to which gaseous oxygen is supplied using gaseous oxygen or another carrier gas, and further into this area. By supplying the endothermic substance directly, the dephosphorization reaction can be most effectively promoted, in this case, the molten iron bath surface in the state of mixing gaseous oxygen, a refining agent, and an endothermic substance (gas or / and solid) from the lance hole of the upper lance. Although it is possible to adopt a method of blowing into, in addition to the above, for example, out of a plurality of lances of the upper lance, only gaseous oxygen from some lances, and from other lances, other than gaseous oxygen or gaseous oxygen as needed. May be supplied to the molten iron bath surface by using a gas (for example, an inert gas such as nitrogen or Ar) as a carrier gas, and a refining agent and a heat absorbing substance (gas or / and solid), respectively. In this case, a main lance having a main lance and a plurality of secondary lances in the center of the lance tip, and gaseous oxygen from the lance, It is particularly preferable to supply a refining agent and a heat absorbing substance (gas or / and a solid) to the molten iron bath surface, respectively, from the ball, if necessary, using gaseous oxygen or a gas other than the above-described gaseous oxygen as a carrier gas. The blowing and refining of the refining agent and the endothermic material may be carried out using another upper lance, but in any case, as described above, the refining agent and the endothermic material (gas or / And solid) is particularly preferably blown into the molten iron bath surface with gaseous oxygen.

14 (a) to 14 (e) show some examples of supply forms of gaseous oxygen, a refining agent, and an endothermic material to the molten iron bath surface using the upper lance. Among these, FIG. 14 (a) is a form in which gaseous oxygen, a refining agent, and an endothermic substance (gas or / and solid) are mixed and supplied from a lance hole (blown into a molten iron bath surface). FIG. In the form of supplying gaseous oxygen and a refining agent from the lance hole and gaseous oxygen and endothermic material (gas or / and solid) from the other lance, respectively (blown into the molten iron bath surface), FIG. 14C shows a part of the lance hole. The carrier gas and the refining agent other than gaseous oxygen are supplied from the other lance, and the gaseous oxygen and the endothermic substance (gas or / and solid) are respectively supplied (blown into the molten iron bath surface). In the form of supplying gas endothermic material and refining agent from the lance hole and gaseous oxygen and endothermic material (gas or / and solid) from the other lance hole (blown into the molten iron bath surface), FIG. Endothermic gaseous oxygen and refiner from the ball, and endothermic gas from other lances It is for supplying quality or gas absorbing material and the solid absorbing material, respectively (that taken into the molten iron bath surface) shape. However, the form of supply of the gaseous oxygen, the refining agent and the endothermic material to the molten iron bath surface is not limited to these.

As described above, CaCO ₃ , Ca (OH) ₂ and CaMg (CO ₃ ) _{2 form} CaO by pyrolysis, and the CaO functions as a refining agent in the solid endothermic material. The solid endothermic material may be supplied in place of part or all of the refining agent (mainly quicklime), and dephosphorization treatment may be performed using CaO generated from this material as a substantial refining agent. That is, in this case, instead of a part or all of the CaO refining agent, in the molten iron bath area to which gaseous oxygen is supplied, it is a refiner generating material and a substance which absorbs heat of molten iron by chemical reaction and / or pyrolysis reaction, One or more selected from CaCO ₃ , Ca (OH) ₂ and CaMg (CO ₃ ) ₂ (hereinafter referred to as “refining agent generation / heat absorbing substance”) are supplied.

According to this method, the by in generating said refiner supplied to the molten iron bath surface and a heat absorbing material thermal decomposition at the same time that the heat absorption of the molten iron, CO ₂ or H ₂ O which the CaO and the heat absorbing material is a refiner by the pyrolysis is generated, This CO ₂ or H ₂ O reacts with Fe to further endotherm the molten iron, and at the same time, the same effect as supplying a CaO-based refiner and an endothermic material together in the molten iron bath area where gaseous oxygen is supplied. Can be obtained, and as a result, high dephosphorization reaction efficiency can be obtained.

In this case as well, for the same reason as described above, it is preferable that the above-mentioned refining agent generating / heat absorbing substance is supplied to a region called “hot spot” generated by the feeding by the upper lance, even in the molten iron bath area to which gaseous oxygen is supplied. .

The refining agent generating / heat absorbing substance is usually added in the form of unbaked or semi-baked limestone or roadmite. If the particle size of the refining agent / heat absorbing substance is too large, pyrolysis or the like does not proceed quickly, and therefore it is preferable that the refining agent is a powder having an average particle diameter of 5 mm or less.

In addition, the above-mentioned refiner production | generation endothermic substance may be used together with the gas endothermic substance mentioned above, and a gas endothermic substance is used as a part or all part of the carrier gas at the time of supplying a refiner production | generation endothermic substance to a molten iron bath surface. You may also do it.

There is no particular restriction on the method of adding the refining agent and the endothermic material, but it is possible to add the refining agent and the endothermic material by blowing into the molten iron bath surface by a squeezing lance or other lances, or by loading the moistener (loading with a shooter or the like). In order to reliably supply to the molten iron bath surface area (especially "hot spot") supplied with oxygen, and to obtain an effect as described above, the molten iron bath surface is supplied to the molten iron bath surface by a lance, in particular, to the molten iron bath surface by a top lance. It is preferable to supply.

In addition, in the case of supplying the refining material and the heat absorbing material to the molten iron bath surface by the squeezing lance, (1) The refiner generating and absorbing material is mixed with gaseous oxygen (with gas oxygen as the carrier gas) and supplied from the same lance to the molten iron bath surface. Method 2) A method for producing refiner and endothermic material and gaseous oxygen into a lance through separate gas supply lines, and supplying them to the molten iron bath surface from separate lances. Gas may be used).

The method of (1) above is more preferable from the viewpoint of reliably supplying the refiner production / heat absorbing material to the molten iron bath area supplied with gaseous oxygen. However, the method of (2) above also provides a refiner production / heat absorbing material supplied through a predetermined lance hole. It can be supplied to the molten iron bath surface area | region to which gaseous oxygen was supplied through another lance hole. Specifically, for example, a gas other than gaseous oxygen is used as a carrier gas from the central lance hole at the tip of the upper lance to supply the refiner generation and endothermic material, and gaseous oxygen is supplied from other lances around the central lance hole. Etc. are preferable. An inert gas such as N ₂ or Ar is suitable as the carrier gas, and as described later, a gas endothermic substance (for example, CO ₂ ) may be used as the carrier gas.

Moreover, in the method of ①, gaseous oxygen obtained by mixing only gaseous oxygen from some of the lances and from other lances and refining / heat absorbing substance can be supplied to the molten iron bath surface, respectively.

In order to supply the refining agent generation and endothermic material with gaseous oxygen to the molten iron bath through the upper lance, for example, part of the oxygen supply line (header, piping, gas oxygen passage in the lance, etc.) of the upper lance or It is good to supply a refiner production | generation and an endothermic substance to all, and to mix with gaseous oxygen.

In addition, the refiner generation / heat absorbing substance may be supplied to the molten iron bath surface using a supply means other than the upper lance (for example, another lance). As a lance other than the upper lance, the powder may be supplied to a predetermined position in the furnace like the upper lance, and sub-lances used for sampling, temperature measurement, and the like can also be used if the cooling capacity in the furnace is not a problem. . In addition, even if the device is an injection device such as a shooter or an injection device, it may be used as long as there is no problem in the contents at high temperature, the precision of the injection position, or the like.

The gaseous oxygen used to generate the refinery and supply the endothermic material may be either pure oxygen gas or oxygen-containing gas.

The first to seventh embodiments of the present invention described above may be performed alone, respectively, and the conditions of two or more embodiments (however, the second embodiment is a ladle type or topidoca type container as a refining container). (Limited to the case of using the above) may be performed in combination, but it goes without saying that the more the conditions to be combined, the more the effect of the method of the present invention can be enhanced.

As described above, according to the method of the present invention, the dephosphorization treatment can be efficiently performed with the minimum amount of refiner added. However, as a further effect, the properties of the slag to be produced are those of the solid phase, so that the slag at the time of tapping after treatment There is a big advantage that the loss can be properly prevented.

If the dephosphorization reaction efficiency is improved in the dephosphorization treatment, the phosphorus concentration in the slag increases, so that the slag together with the metal during tapping after dephosphorization treatment (particularly when tapping from a refining vessel having a tapping outlet such as a converter type container) is used. It is important that no spills occur. That is, when phosphorus distribution Lp = 200 dephosphorization treatment is carried out, and P content of 0.015 mass% (standard value: 0.020 mass%) in molten iron | metal after treatment is carried out, when slag about 5 kg / melting | molding | molten iron ton flows out, phosphorus will be 0.015. Since it is carried in the mass% content and the decarburization converter, the lime for dephosphorization is required also in the decarburization converter. In this way, however, the original purpose of the charter preliminary treatment cannot be achieved. Therefore, prevention of slag outflow to the next process of dephosphorized slag becomes important.

Conventionally, as a method for minimizing slag outflow to the next step after dephosphorization treatment using a converter vessel, (1) slag cut technique during tapping from the converter vessel, and (2) slag after treatment There are a method of reducing the fluidity of the slag by controlling the composition, (3) a method of removing slag from the ladle after tapping, and the like.

However, these conventional methods are not able to stably prevent the loss of slag, are expensive because of the use of consumables, and because the work takes time, the molten iron temperature is lowered, and iron production is reduced with slag removal. There is a problem.

On the other hand, according to the present invention method, as described above, the slag generated in the molten iron bathing area centered on the hot spot and sequentially pushed out of the outside becomes a stable solid body, and thus, at the end of the dephosphorization treatment. The slag has a very low fluidity compared to slag produced by the conventional dephosphorization treatment. As a result, slag outflow during tapping after completion of dephosphorization treatment (particularly, when tapping from a refining vessel having a tapping outlet such as a converter type container) is obtained. Can be effectively prevented. Also, as previously described, the effect by the amount of or no added CaF ₂ or CaF ₂ to 1kg / ton molten iron or less, there can be more enhanced by suppressing an increase in the fluidity of the slag.

Hereinafter, the slag produced by the method of the present invention will be described in comparison with the slag produced by the conventional method in which the slag outflow is prevented at the time of tapping. Fig. 15 shows the state of slag / metal at the start of tapping in the converter-type container. In the conventional method shown in Fig. 15 (a), by lowering the slag basicity or adding a large amount of CaF ₂ . Since the slag is actively melted, the slag is forming and the slag thickness is increasing. For this reason, when a furnace is tilted at the time of tapping, since slag will initially pass through a tap opening, slag outflow will inevitably generate | occur | produce. On the other hand, in the case of the present invention method shown in Fig. 15 (b), the slag thickness is extremely thin because the slag exists in the state of the solid body, and the slag outflow occurring at the start of tapping is negligible.

Fig. 16 shows the state of slag / metal near the tapping port at the end of tapping. Immediately before the end of tapping, the metal depth becomes shallow and vortices of the metal are generated. However, in the conventional method shown in Fig. 6 (a), the molten slag of the metal is rolled out and flowed out. On the other hand, in the case of the present invention method shown in Fig. 16 (b), since the slag is a solid main body, the slags interfere with and coalesce on the vortex of the metal, and therefore the slag is hardly curled into the vortex of the metal.

1 is a graph showing the relationship between the slag content after dephosphorization and P content in molten iron.

2 is a graph showing the relationship between the Si content in the molten iron before the dephosphorization treatment and the slag amount after the dephosphorization treatment.

3 is an explanatory diagram showing an embodiment of the present invention method using a converter container.

4 is a graph showing the relationship between the ratio of the amount of refining agent added to the refining agent total amount and the amount of necessary lime in the second embodiment of the present invention method.

Fig. 5 shows the second embodiment of the method of the present invention, in which the entire amount of the refining agent is added by blowing into the molten iron bath surface through the upper blowing lance and blowing into the molten iron through the immersion lance or / and the blowing nozzle. , The graph showing the relationship between the ratio of the amount of refiner added to the amount of refiner added and the dephosphorization rate through the squeezing lance.

6 is an explanatory diagram showing an example of an embodiment of the second embodiment of the present invention method.

FIG. 7 is a graph showing the relationship between the CaO raw unit and the dephosphorization efficiency required for the P content in the molten iron after the dephosphorization treatment to be 0.012 mass% in the third embodiment and the conventional method of the present invention method.

8 is a graph showing the relationship between the Si content in molten iron and the amount of required lime in the fourth embodiment and the conventional method of the present invention.

Fig. 9 is a graph showing the relationship between the required lime amount for dephosphorization and the lime efficiency η _{cao for the} molten iron after dephosphorization treatment and the P content in the molten iron after the fourth embodiment of the present invention and the conventional method.

Fig. 10 shows the ratio X / W _cao _P of the lime amount X injected to the molten iron bath surface from the upper lance and the lime amount W _cao _P for de-P in the molten iron after dephosphorization treatment in the fourth embodiment of the present invention method. It is a graph showing the relationship with P content.

Fig. 11 shows the depth L and the dephosphorization efficiency and the P content in the molten iron after the dephosphorization treatment in the fifth embodiment of the method of the present invention, in which the depression of the molten iron formed on the molten iron bath surface by blowing of a gaseous oxygen or a gaseous oxygen refining agent into the carrier gas This graph shows the relationship between

12 is a graph showing the relationship between the Si content in molten iron and the molten iron temperature after the dephosphorization treatment and the dephosphorizing lime efficiency in the dephosphorization treatment without CaF _{2 addition} in the sixth embodiment of the present invention method.

FIG. 13 is a graph showing the relationship between CaF ₂ addition amount and demineralization efficiency in the dephosphorization treatment at a molten iron temperature of 1360 ° C. to 1450 ° C. after the dephosphorization treatment in the sixth embodiment of the present invention method.

FIG. 14: is explanatory drawing which shows the example of the supply form to the molten iron bath surface of gaseous oxygen, a refining agent, and an endothermic substance in 7th Embodiment of this invention method.

15 is an explanatory view schematically showing a state of slag / metal at the start of tapping in the conventional method using the converter-type container and the present invention method.

FIG. 16: is explanatory drawing which shows typically the state of the slag / metal in the tapping opening vicinity of the end of tapping in the conventional method and this invention method using a converter container.

Fig. 17 shows the relationship between the ratio A / B of the gas supply rate A and the gas supply rate B of the CaO refining agent in the example of the first embodiment of the present invention and the P content in the molten iron after dephosphorization treatment. A graph representing.

Example 1

The molten iron drawn from the blast furnace is subjected to de-silification in the ladle according to the columnar and the need, and desulfurization in the molten ladle using mechanical stirring. After the yellowing treatment, dephosphorization treatment was performed in a converter-type container (300 tons). The molten iron component was C: 4.5-4.7 mass%, Si: 0.01-10.2 mass%, Mn: 0.15-0.25 mass%, P: 0.1-10 mass%, S: 0.001-0.003 mass%. Lime powder having a particle size of 1 mm or less was used as a dephosphorizing refiner, and this was blown into a bath surface of the molten iron with oxygen as a carrier gas through a lance. CaF ₂ was not added in the refiner. Blowing time was made constant for 10 minutes, and nitrogen gas was supplied from 0.05 to 0.15 Nm <^3> / min / melting | tonton in order to stir molten metal from a furnace. The raw units of lime and oxygen change depending on the Si content in the molten iron, but the values of all lime and oxygen except desulfurization (dicalcium silicate: stoichiometry of 2CaO and SiO ₂ ) are 3.5 kg / It was a constant charter ton, 9Nm ³ / charter ton. The ratio A / B between the feed rate B of lime blown into the molten iron bath surface (kg / min / melting ton) and the feed rate A of gaseous oxygen injected into the molten iron bath surface (Nm ³ / min / melting ton) was 1.7. The amount of lime added was within the range of the sum of the amounts of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined in the above formulas (5) and (6). In addition, the depth L (L value defined by Formula (7) mentioned above) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. In addition, the molten iron temperature before and behind dephosphorization treatment was 1250-1350 degreeC. The amount of slag after the treatment was calculated from the mass balance between the amount of added lime and the CaO concentration (slag analysis value) in the slag.

The results of each example are shown in Table 1 together with the dephosphorization treatment conditions. In addition, each average value shown in Table 1 is 5 kg / molten iron-10 kg / molten iron ton, 10 kg / molten iron ton-20 kg / molten iron ton, 20 kg / molten iron ton-30 kg / molten iron ton, 30 kg / molten iron ton-40 kg / The value of dephosphorization treatment of 6-72 ch is averaged for the range of slag amount after each treatment of molten iron ton and 40 kg / molten ton more than 50 kg / molten ton.                 

Example 2

The molten iron drawn out from the blast furnace was subjected to desilification in the molten iron ladle in accordance with the columnar and the necessity, and then desulfurized in the molten iron ladle using mechanical stirring, and then dephosphorized in the converter vessel (300 tons). P content of molten iron before dephosphorization was 0.10 to 0.11 mass%, and Si content was 0.15 mass% or less. The molten iron temperature before and after this dephosphorization treatment shall be 1250-1350 degreeC, and as a dephosphorizing refiner, it is the CaO main body slaked lime and the thing extracted below the particle size 200 mesh is used, and the raw unit of CaO is used. Was 5 to 15 kg / melting ton depending on the Si content in the molten iron.

In this dephosphorization treatment, the refiner and the oxygen source were supplied to the bath surface by gaseous oxygen as a carrier gas through a top blowing lance (flushing time: 10 minutes). The operation was performed under various conditions in which the ratio A / B of the supply rate A of oxygen (Nm ³ / min / melting ton) and the refining agent supply rate B (kg / min / melting ton) was different. In addition, nitrogen gas was blown into the molten iron from a bottom blowing nozzle at a flow rate of 0.05 to 0.15 Nm ³ / min / melting ton as a gas for stirring. CaF ₂ was not added to the refining agent, and the amount of slag after the treatment was 30 kg / mol ton or less. The amount of lime added was within the range of the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined in the above formulas (5) and (6). In addition, the depth L (L value defined by Formula (7) mentioned above) formed in the molten metal bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag.

17 shows the relationship between the ratio A / B of the gas supply rate A (Nm ³ / min / melting ton) and the refining agent supply rate B (kg / min / melting ton) to the P content in the molten iron after dephosphorization treatment. It was. According to the present invention, the A / B of the present invention is in the region of 0.3 to 7 and the content of P in the molten iron after dephosphorization is 0.015 mass% or less, which is the target [P] concentration. In particular, the content of Si in the molten iron before dephosphorization is 0.10 mass. In the case of% or less, [P] <0.010 mass% which is a low P standard is achieved stably. In addition, the fact that A / B is in the region of 1.2 to 2.5 is particularly low in the [P], and it can be seen that the highest dephosphorization reaction efficiency can be obtained in this region.

On the other hand, in the area where A / B is less than 0.3 and more than 7, the P content in molten iron after dephosphorization does not reach 0.015 mass% or less which is a target [P] concentration.

Example 3

After degreasing the molten iron drawn from the blast furnace on the columnar, it is repaired in the molten iron ladle, desulfurized in the molten iron ladle, discharged, and then the molten iron ladle is dephosphorized. station) and dephosphorization was carried out.

In the dephosphorization treatment, lime powder (refining agent) was blown into the molten iron bath surface using gaseous oxygen as a carrier gas through a top blowing lance, and lime powder was blown into the molten iron through an immersed lance. In the comparative example, the lime powder was blown into the molten iron through the immersion lance, without blowing the lime powder by the upper lance. In all cases, the treatment time was 20 minutes. The amount of slag after the treatment was set to 20 kg / molten iron or less. In the example of the present invention, the amount of lime added is the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined by the formulas (5) and (6) described above. It was to be in a range. In addition, the depth L (L value defined by Formula (7) mentioned above) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. In addition, the molten iron temperature before and after dephosphorization treatment was 1300-1320 degreeC. The amount of slag after the treatment was calculated from the mass balance of the CaO concentration between the amount of lime addition and the CaO concentration (slag analysis value) in the slag.

The results of each example are shown in Table 2 together with the dephosphorization treatment conditions.                 

Example 4

The molten iron drawn out from the blast furnace was subjected to de-silification in the molten iron ladle in accordance with the columnar and the necessity, desulfurized in the molten iron ladle using mechanical stirring, and then dephosphorized in the converter vessel (300 tons). In this dephosphorization treatment, the molten iron temperature before and after the treatment is set at 1250 to 1350 ° C, the gaseous oxygen is blown into the molten iron bath surface through the upper blowing lance, and (1) the lime powder having a particle diameter of 1 mm or less (refining agent) using the gaseous oxygen as a carrier gas. ) Was added to the molten iron bath surface, or (2) The refiner was added by any of the methods of loading the lime (refining agent) having a particle size of 1 to 3 mm. Nitrogen gas was blown from the furnace of the converter-type vessel at a feed amount of 0.05 to 0.15 Nm ³ / min / melting ton, followed by 9 minutes of dephosphorization while stirring the molten iron. The slag amount after the treatment was 30 kg / molten tonne or less. In the example of the present invention, the amount of lime added is the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined by the formulas (5) and (6) described above. It was to be in a range. In addition, the depth L (L value defined by Formula (7) mentioned above) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag.

The result of each Example is shown in Table 3 with dephosphorization treatment conditions.                 

Example 5

After degreasing the molten iron from the blast furnace in the columnar, it was repaired in the molten iron ladle to de-silicate in the molten iron ladle, and after discharging, the molten iron was charged into a converter vessel (300 tons).

In the dephosphorization treatment, a lime powder (refining agent) is blown into the molten iron bath surface using oxygen gas as a carrier gas using a wicking lance, and in some embodiments, the filling of the bulk lime is carried out. top-charging) was performed together. In addition, in the comparative example, the bulk lime was added by the charging of the lettuce without blowing the lime powder through the upper lance. In each of the examples, nitrogen gas was blown from the furnace of the converter-type vessel at a feed amount of 0.07 to 0.12 Nm ³ / min / melting ton, and dephosphorization was performed for 8 to 14 minutes. In this dephosphorization treatment, the molten iron temperature before and after the treatment was 1250 to 1350 ° C., and the slag amount after the treatment was 30 kg / molten iron or less. In the present invention, the ratio A / B of the feed rate B of lime blown into the molten iron bath surface (kg / min / melting ton) and the feed rate A of gaseous oxygen blown into the molten iron bath surface (Nm ³ / min / melting ton) Was set to 1.7. In addition, the molten iron temperature before and behind dephosphorization treatment was 1250-1350 degreeC. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag.

The result of each Example is shown to Tables 4-7 with dephosphorization treatment conditions.                 

Example 6

After degreasing the molten iron from the blast furnace at the columnar, it is repaired in the molten iron ladle, de-siliculated in the molten iron ladle, and after discharging, the molten iron is charged into a converter vessel (300 tons) and dephosphorized. It was. In this dephosphorization treatment, gaseous oxygen is blown into the molten iron bath surface through a top blowing lance, and ① lime gas (refining agent) having a particle size of 3 mm or less is blown into the molten iron bath surface using the gaseous oxygen as a carrier gas, or ② calcined lime (refining agent). Refining agent was added by any method of the method of charging. Nitrogen gas was blown from the furnace of the converter-type vessel at a supply amount of 0.1 Nm ³ / min / melting ton, and the dephosphorization treatment was performed for 10 to 11 minutes while stirring the molten iron. In addition, the molten iron temperature and the amount of scrap added before the dephosphorization treatment were adjusted, and the molten iron temperature at the end of the dephosphorization treatment was controlled. The slag amount after the treatment was 30 kg / molten tonne or less. In the example of the present invention, the amount of lime added is the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined by the formulas (5) and (6) described above. It was to be in a range. Moreover, the depth L (L value defined by Formula (7) mentioned above) formed in the molten iron bath surface by blowing the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. The amount of slag after the treatment was calculated from the mass balance of CaO concentration of the added lime and the slag analysis value.

The results of each example are shown in Table 8 together with the dephosphorization treatment conditions.

Example 7

After degreasing the molten iron from the blast furnace in the column, it is repaired in the molten iron ladle, de-silified in the molten iron ladle, and after discharging, the molten iron is charged into a converter vessel (300 tons) for dephosphorization treatment. The dephosphorization treatment was performed. In this dephosphorization treatment, a lime powder (refining agent) and an endothermic substance having a particle diameter of 1 mm or less were blown into the molten iron bath surface using gaseous oxygen as a carrier gas through a top blowing lance. As the endothermic material, CaCO ₃ or Ca (OH) ₂ (all of which have a particle diameter of 1 mm or less) was used and mixed in advance to a predetermined ratio with lime. Nitrogen gas was blown from the furnace of the converter-type vessel at a supply amount of 0.1 Nm ³ / min / melting ton, and the dephosphorization treatment was performed for 10 to 11 minutes while stirring the molten iron. In addition, the molten iron temperature before dephosphorization and the amount of scrap addition were adjusted, and the molten iron temperature at the end of dephosphorization was controlled. The slag amount after the treatment was 30 kg / molten tonne or less. In the example of the present invention, the amount of lime added is the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined by the formulas (5) and (6) described above. It was to be in a range. In addition, the depth L (L value defined by Formula (7) mentioned above) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. The amount of slag after the treatment was calculated from the mass balance of CaO concentration of the added lime and the slag analysis value.

The results of each example are shown in Table 9 together with the dephosphorization treatment conditions.                 

Example 8

After removing the molten iron from the blast furnace in the molten iron ladle, after discharging, the molten iron was charged to a converter-type container (300 tons) and dephosphorized. In this dephosphorization treatment, a stirring gas (nitrogen) of about 0.1 Nm ³ / min / melting ton is blown from the bottom of the converter-type vessel, the molten iron is stirred, and a gaseous oxygen, lime powder ( CaO-based refiner) and a gas endothermic material were supplied to the molten iron bath surface. In addition, CaF ₂ was not added during scouring. The slag amount after the treatment was 30 kg / molten tonne or less. The ratio A / B between the feed rate B of lime blown into the molten iron bath surface (kg / min / melting ton) and the feed rate A of gaseous oxygen injected into the molten iron bath surface (Nm ³ / min / melting ton) was 1.7. The amount of lime added was within the range of the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined in the above formulas (5) and (6). In addition, the depth L (L value defined by Formula (7) mentioned above) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. In addition, the molten iron temperature before and behind dephosphorization treatment was 1250-1350 degreeC. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag.

As the top blowing oxygen-feed lance, one having a central hole and three peripheral holes was used as the lance hole.

Lime powder has a particle diameter of 3 mm or less, and this is cut out using gaseous oxygen as a carrier gas from an extraction device, and the inside of the pipe is conveyed to the upper lance and supplied to the molten iron bath with gaseous oxygen from the central hole. To be supplied. On the other hand, gas oxygen was supplied to the upper lance through the other piping line, and was supplied to the molten iron bath surface from the surrounding hole. The total delivery amount was 1.5 Nm ³ / min / melting ton.

Gas endothermic material was added to both gaseous oxygen lines so as to have a predetermined concentration. Carbon dioxide and water vapor were used as this gas endothermic substance, and the mixing ratio with respect to gaseous oxygen was 10-40 volume% (outer water with respect to oxygen gas 100).

In the comparative example, gaseous oxygen was supplied to the molten iron bath surface from the wicking lance, and lump lime (CaO-based refining agent) was loaded at the same time.

The result of each Example is shown in Table 10 with dephosphorization treatment conditions.

Example 9

The blast furnace pig iron was subjected to de-silification in the ladle, then excreted and subsequently dephosphorized in the ladle. In this dephosphorization treatment, 3Nm ³ of nitrogen is injected into the molten iron from one immersion lance every minute to stir the molten iron, and gaseous oxygen, lime powder (CaO-based refiner), and endothermic substance are separated from the bath surface by using the upper lance. It was supplied in any form of ④. In addition, CaF ₂ was not added during scouring. The slag amount after the treatment was 30 kg / molten tonne or less. The ratio A / B between the feed rate B of lime blown into the molten iron bath surface (kg / min / melting ton) and the feed rate A of gaseous oxygen injected into the molten iron bath surface (Nm ³ / min / melting ton) was 1.7. The amount of lime added was within the range of the sum of the amount of lime W _cao _P (kg / melting ton) and the amount of lime W _cao _Si (kg / melting ton) defined in the above formulas (5) and (6). In addition, the depth L (L value defined by Formula (7) mentioned above) formed in the molten iron bath surface by blowing of the refiner which uses gaseous oxygen as a carrier gas was controlled in the range of 200-500 mm. On the other hand, the molten iron temperature before and after dephosphorization treatment was 1250-1350 degreeC. The amount of slag after the treatment was calculated from the mass balance between the amount of lime added and the CaO concentration (slag analysis value) in the slag.

① Example of the Invention: Gas oxygen, lime powder and CO ₂ are supplied in the upper lance.

② Example of the Invention: Gas gas, lime powder, CaCO ₃ (limestone) or Ca (OH) ₂ (lime lime) are supplied in the upper lance.

③ Example of the Invention: The gaseous oxygen, lime powder, CO ₂ , CaCO ₃ (limestone) are supplied in the upper lance.

④ Example of the Invention: The gaseous oxygen, CaCO ₃ (limestone) or Ca (OH) ₂ (limestone) is fed in the upper lance.

Lime powder, CaCO ₃ (limestone) and Ca (OH) ₂ are those having a particle diameter of 1 mm or less, and they are cut out using a gaseous oxygen as a carrier gas from the cutting device to convey the inside of the pipe, and at the same time, other pipes are removed from the upper lance inlet. It was combined with the gaseous oxygen supplied through it, and it supplied to the bath surface with gaseous oxygen fractionation from three lance holes of a top lance tip. Total delivery volume was set to 6000 Nm ³ every hour.

In CO ₂ , the mixing ratio to gaseous oxygen was 25% by volume (external water to gaseous oxygen 100). Further, seokhoebun, CaCO ₃ (limestone), Ca (OH) ₂ was added so as to have minute (每分) 70~80kg in an amount in terms of CaO.

In addition, in the comparative example, while supplying gaseous oxygen to the molten iron bath surface through the upper lance, lime powder was injected into the molten iron through the immersion lance.

The results of each example are shown in Table 11 together with the dephosphorization treatment conditions.                 

The present invention is used to produce molten iron having a low phosphorus content in an intermediate step of steel production.

Claims (33)

Low phosphorus vessels are obtained by adding an oxygen source and a refining agent, which is a CaO source, into a vessel having a molten iron and performing dephosphorization treatment, which is a molten iron preliminary treatment. In the method of manufacturing i) Degassing is carried out by blowing gaseous oxygen and at least some of the refining agent into the hot spots on the bath surface of the molten iron by blowing gaseous oxygen through a top blowing lance. When performing, the slag amount after treatment is set to 30 kg / melting ton or less with respect to molten iron whose Si content is 0.15 mass% or less. delete delete delete delete delete delete delete delete The method of claim 1, The feed rate B (kg / min / melting ton) of CaO of the refiner blown into the molten iron bath surface, and the feed rate A (Nm ³ / min / melting ton) of gaseous oxygen injected into the molten iron bath surface are represented by the following formula (1) The method of producing a low citation ship, characterized in that to satisfy. 0.3? A / B? (One) The method of claim 10, The feed rate B (kg / min / melting ton) of CaO of the refinery blown into the molten iron bath surface, and the feed rate A (Nm ³ / min / melting ton) of gaseous oxygen injected into the molten iron bath surface are represented by the following formula (2) The method of producing a low citation ship, characterized in that to satisfy. 1.2? A / B? (2) Ladle or topedo-car type vessels are used as vessels to hold the molten iron, and immersed into the molten iron bath by blowing gaseous oxygen and at least a portion of the refiner into the molten iron bath through an upper lance. The amount of gaseous oxygen blown into the molten iron bath surface through the upper lance is 0.7 Nm ³ / when blowing gas containing at least a portion of the powder which is at least partially refined through the lance or blowing nozzle into the molten iron. The method for producing a low citation vessel, characterized in that it is less than min / melting ton and the addition amount of the refining agent through the top blowing lance is 20 to 80% by mass of the total amount of the refining agent. delete delete delete delete The method according to claim 1 or 12, wherein A process for producing a low-phosphorus vessel characterized by performing a dephosphorization treatment so that the supply rate of the refiner blown into the molten iron bath surface and the gas oxygen supply rate satisfy the following formulas (3) and (4). (C1 / D1)> (C2 / D2)... (3) C1> C2... (4)     However, C1: Average value of refining agent supply rate in terms of CaO in the dephosphorization treatment (kg / min / melting ton)          C2: Average value of refining agent feed rate in terms of CaO in the latter stage of dephosphorization (kg / min / melting ton) D1: Average value of gaseous oxygen feed rate in dephosphorization (Nm ³ / min / melting ton) D2: Average value of gaseous oxygen supply rate in the late dephosphorization treatment (Nm ³ / min / melting ton) The method of claim 17, A method for producing a low citation vessel, characterized in that during the dephosphorization treatment, the refining feed rate and the gaseous oxygen feed rate in terms of CaO are changed continuously or stepwise. The method according to claim 1 or 12, wherein Through sangchwi lance and oxygen gas at the same time as performing the dephosphorization treatment with at least blowing a portion refiner to the molten iron bath surface, in the art dephosphorization process, a refiner, to 5 lime amount to be calculated by the formula W _cao _P (kg / molten iron A method for producing a low citation vessel, characterized by adding a lime in an amount obtained by adding ton) and the amount of lime W _cao _Si (kg / melting ton) obtained by the following formula (6). W _cao _P = (melting line [P]-target [P]) x (10/62) x 56 x 3 / η _cao . (5) However, molten iron [P]: P concentration (mass%) in molten iron before dephosphorization treatment     Target [P]: P concentration (mass%) in molten iron | metal after target dephosphorization treatment η _cao (lime efficiency) = 0.5 to 1 W _cao _Si = molten iron [Si] x (10/28) x 56 x 2. (6) However, molten iron [Si]: Si concentration (mass%) in molten iron before dephosphorization treatment The method of claim 19, Lime amount W _cao _P that cited manufacturing method of the line that at least 80% by weight of lime, characterized in that the blown in the molten iron bath surface through the lance sangchwi (where, η = 1 W _{cao cao} _P which is obtained in). The method of claim 19, As a refining agent corresponding to the amount of lime W _cao _Si, at least one selected from iron slag containing lime powder, calcined lime, calcareous stone, and unreacted CaO. Method for producing a low citation ship, characterized in that using. The method according to claim 1 or 12, wherein The depth L of the recessed portion formed in the molten iron bath surface by the blowing of gaseous oxygen or blowing of a gaseous oxygen carrier gas as defined by the following formula (7) is controlled to 200 to 500 mm. Manufacturing method. L = L ₀ × exp {(-0.78 × L _H ) / L ₀ }... (7) L ₀ = 63 × {(F ₀₂ / n) / d _t } ^2/3 However, L _H : Lance height of upper lance (mm) F ₀₂ : Gas Oxygen Supply Rate from Upper Lance (Nm ³ / hr)     n: Nozzle air of the upper lance d _t : Nozzle diameter of nozzle lance (nozzle 孔徑, mm) (However, if the nozzle diameters of a plurality of nozzle holes are different, average nozzle diameter of all nozzle holes) delete The method according to claim 1 or 12, wherein Melting temperature at the end of dephosphorization treatment at the end of dephosphorization treatment by degassing gaseous oxygen and at least a portion of the refiner into the molten iron bath surface under a condition of not adding CaF ₂ other than that contained as an unavoidable impurity. The manufacturing method of the low citation ship characterized by setting it as 1360 degreeC-1450 degreeC. The method according to claim 1 or 12, wherein A method for producing a low citation vessel, characterized by supplying a substance that absorbs heat of the molten iron by a chemical reaction or a pyrolysis reaction to a molten iron bath surface region to which gaseous oxygen is supplied. The method of claim 25, A method for producing a low citation vessel, characterized by supplying at least a portion of a material that absorbs heat of the molten iron by a chemical reaction or a pyrolysis reaction to a hot spot generated in the molten iron bath surface by blowing gaseous oxygen. delete delete delete delete delete delete delete

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