WO2018123991A1 - Molten pig iron pretreatment method and method for producing ultra-low phosphorus steel - Google Patents

Molten pig iron pretreatment method and method for producing ultra-low phosphorus steel Download PDF

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Publication number
WO2018123991A1
WO2018123991A1 PCT/JP2017/046483 JP2017046483W WO2018123991A1 WO 2018123991 A1 WO2018123991 A1 WO 2018123991A1 JP 2017046483 W JP2017046483 W JP 2017046483W WO 2018123991 A1 WO2018123991 A1 WO 2018123991A1
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hot metal
pretreatment
iron oxide
concentration
dephosphorization
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PCT/JP2017/046483
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French (fr)
Japanese (ja)
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慎平 小野
公則 筈見
靖久 立入
進 工藤
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新日鐵住金株式会社
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Priority to CN201780059237.9A priority Critical patent/CN109790589A/en
Priority to JP2018559473A priority patent/JP6773131B2/en
Priority to KR1020197017742A priority patent/KR102189097B1/en
Publication of WO2018123991A1 publication Critical patent/WO2018123991A1/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/02—Dephosphorising or desulfurising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/04—Removing impurities other than carbon, phosphorus or sulfur
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the present invention relates to a pretreatment method for efficiently reducing the Si concentration and the P concentration of molten iron and a method for producing ultra-low phosphorus steel in a kneading vehicle.
  • hot metal pretreatment for removing silicon, phosphorus, sulfur and the like is performed.
  • the hot metal discharged from the blast furnace is still present in the ironing, decanting iron, or kneading vehicle
  • the hot metal as a refining agent, lime-based flux, oxidizer, and / or soda ash
  • a system flux or the like is blown with a carrier gas (for example, nitrogen or oxygen), or directly added from above, and silicon, phosphorus, sulfur, or the like is transferred to the slag to be removed.
  • converter type hot metal pretreatment a process using a converter for hot metal pretreatment (converter type hot metal pretreatment) has also been developed.
  • the converter type hot metal preliminary treatment is generally performed by a two-furnace system using a dephosphorization converter and a decarburization converter.
  • Patent Document 1 discloses that the converter is tilted after the dephosphorization process.
  • the method of patent document 1 has a great merit that it is a one-furnace system and a high heat tolerance by hot recycling of decarburized slag.
  • the concentration of the main slag source silicon (Si) in the molten iron becomes low, making intermediate exhaustion difficult. Become.
  • Si main slag source silicon
  • SiO 2 SiO 2 is newly added as a slag source.
  • an uneconomical process such as increasing the silicon concentration of the hot metal again is necessary.
  • the P concentration in the hot metal is sufficiently reduced by the hot metal pretreatment, or the molten steel that has been subjected to dephosphorization treatment in the converter is once removed and the total amount of dephosphorized slag is obtained. Is required to be discharged from the system and decarburized and dephosphorized again in the same converter.
  • the ultra-low phosphorus steel is a steel having a phosphorus content of 0.01% or less.
  • the dephosphorization reaction proceeds after completion of the desiliconization reaction. Therefore, when the P concentration of the hot metal is sufficiently reduced by the hot metal pretreatment as described above, it is necessary to reduce the Si concentration of the hot metal to substantially zero in the hot metal pretreatment.
  • Patent Document 2 discloses a method of simultaneously performing desiliconization and dephosphorization from molten iron by simultaneously blowing a flux mainly containing CaO and an oxygen source into the same position under the following conditions.
  • the method disclosed in Patent Document 2 is carried out using a flux containing fluorite.
  • [% Si] 0 initial [Si] concentration
  • fluorite CaF 2
  • fluorine (F) concentration of the formed slag In recent years, elution of fluorine into the environment from civil engineering and construction materials using slag as a raw material is regarded as a problem, and the Environment Agency has also established regulations on fluorine in slag. Further, it is preferable that fluorine in the slag does not affect the refractory of the container used for the pretreatment.
  • Patent Document 3 as a hot metal pretreatment method that does not use fluorite and performs desiliconization and dephosphorization, lime-based flux and an oxidizing agent are blown into hot metal in a refining vessel, and the desiliconization rate is 90%.
  • a method has been proposed in which the main amount of flux is added to the hot metal so that the final basicity of the slag is 1.2 to 2.5.
  • Patent Document 4 discloses that hot metal held in a hot metal holding container is added with an iron oxide source from above the bath surface, and degassed hot metal by blowing a solvent mainly composed of CaO below the bath surface. Disclosed is a method of treating and producing a low phosphorus hot metal.
  • the iron oxide source is arranged such that the charging area on the bath surface of the iron oxide source overlaps with 40% or more of the blowing area on the bath surface of the medium solvent in terms of area ratio. It is characterized by adding.
  • the method disclosed in Patent Document 4 can omit a solvent containing a fluorine source such as fluorite.
  • Patent Document 4 is a one-furnace system similar to the method of Patent Document 1 and involves an intermediate waste process. Patent Document 4 teaches that the generated slag is discharged after the silicon concentration of the hot metal is reduced to a predetermined level by desiliconization treatment in the hot metal ladle. The means for solving this problem is not specifically taught.
  • the slag having a high phosphorus concentration generated by the dephosphorization blowing cannot be completely removed by the intermediate waste removal process, and the slag remains after the intermediate waste removal process. For this reason, it is difficult to melt ultra-low phosphorus steel by the above-mentioned dephosphorization method using a single furnace method.
  • the present invention is based on the current state of the art, and in the hot metal preliminary treatment, before the hot metal treatment by the converter, the silicon concentration in the hot metal is left in the hot metal while leaving an intermediate concentration step in the converter.
  • An object of the present invention is to provide a pretreatment method and a method for melting ultra-low phosphorous steel that improve the efficiency of dephosphorization treatment and desiliconization treatment in the smelting process by reducing the P concentration of the steel.
  • Another object of the present invention is to efficiently reduce the P concentration and Si concentration of hot metal without using CaF 2 in the hot metal pretreatment.
  • the present inventors can proceed with desiliconization treatment and dephosphorization treatment at the same time to appropriately reduce the Si concentration and the P concentration of the hot metal. Based on the idea that efficiency will improve and the efficiency of the entire refining process will improve, we have intensively studied methods for solving the above problems.
  • the hot metal is pretreated so that the Si content is 0.05 to 0.30% by mass and the P content is 0.040 to 0.085% by mass. It has been found that the efficiency of the entire refining process is improved by combining with the intermediate waste process.
  • the present inventors diligently studied conditions for simultaneously performing desiliconization and dephosphorization of hot metal with lime and iron oxide fluxes in the hot metal pretreatment.
  • the change in the Si content and the P content of the hot metal before and after the pretreatment is more than 0.1. It has been found that it is preferable.
  • the composition can be adjusted to be suitable for the next refining process such as a process.
  • the present invention has been made on the basis of the above findings, and the gist thereof is as follows.
  • the preliminary treatment can be performed so as not to interfere with the intermediate waste process in the converter, by using the preliminary treatment method of the present invention, an extremely low phosphorus steel in the refining process by the converter. Can be efficiently melted.
  • the hot metal P concentration and Si concentration can be efficiently reduced without using CaF 2 in the hot metal pretreatment.
  • the hot metal pretreatment method of the present invention is a method of desiliconization by introducing iron oxide, gaseous oxygen, and lime-based flux into the hot metal in the refining vessel.
  • the hot metal pretreatment method for dephosphorization (I) While adding 25 kg / t or more of iron oxide in terms of iron oxide equivalent oxidizer basic unit, (Ii) At the time of the above charging, 60% or more of the iron oxide to be charged is charged from above the refining vessel, (Iii)
  • the hot metal has a Si content of 0.05 to 0.30 mass% and a P content of 0.040 to 0.085 mass%.
  • the hot metal targeted for the pretreatment method of the present invention is Si: 0.80 mass% or less and P: 1.200 mass% or less
  • the hot metal is not limited to a specific component composition, but is a hot metal having a normal component composition. Specifically, for example, hot metal discharged from a blast furnace and hot metal melted in an electric furnace can be used.
  • the container is not limited to a kneading vehicle, and may be a container (for example, a hot metal ladle or the like) for transporting hot metal to the next refining process and capable of performing preliminary refining.
  • FIG. 1 schematically shows an embodiment of hot metal pretreatment using a kneading vehicle as a refining vessel.
  • the lance 3 is immersed in the hot metal 4 from the opening 2 of the kneading wheel 1, and the lime-based flux 5 and / or the oxidizing agent 6 (iron oxide) is conveyed by the carrier gas 7 (gaseous oxygen). Then, blow into the hot metal 4 from the lance 3 for the required time.
  • the carrier gas 7 gaseous oxygen
  • Si and P in the hot metal 4 are oxidized and transferred to the slag 8, and the pretreatment (desiliconization and dephosphorization) of the hot metal 4 proceeds.
  • the pretreatment is interrupted, the kneading vehicle 1 is tilted, and the generated slag 8 is discharged out of the kneading vehicle 1.
  • the pretreatment is restarted with the lime-based flux 5 and the oxidizing agent 6.
  • iron oxide 6a of 60% or more of the iron oxide to be added is From the chute 9 disposed in the opening 2.
  • the iron oxide source examples include mill scale, sintered ore, iron ore, and sintered dust.
  • the lime-based flux may be CaO alone, or may be a mixture of calcium carbonate (CaCO 3 ) or a converter soot whose main component is CaO.
  • the method of the present invention 25 kg / t or more of iron oxide in terms of iron oxide-converted oxidant basic unit is charged into the hot metal, which will be described later.
  • the input amount of iron oxide is the total mass of iron oxide charged into the hot metal charged in the kneading vehicle.
  • the “oxidizing agent basic unit in terms of iron oxide” is a mass obtained by converting the total mass of oxygen supplied for pretreatment of hot metal 1t into FeO in the hot metal pretreatment process.
  • the present inventors diligently conducted quantitative investigations regarding the addition of iron oxide to hot metal, and the iron oxide equivalent oxidizer unit of iron oxide to be added to hot metal, and the iron oxide to be supplied from above the hot metal The percentage (%) was clarified.
  • FIG. 2 shows the ratio of iron oxide introduced from above the kneading vehicle: R FeO (%), the amount of change in P concentration (mass%) ⁇ P and the amount of change in Si concentration (mass%) ⁇ Si before and after the pretreatment. Ratio: A relationship of ⁇ P / ⁇ Si is shown.
  • FIG. 2 shows changes in ⁇ P / ⁇ Si when iron oxide is added to the hot metal, and 35 kg / t of oxidant basic unit converted to iron oxide, and 25 kg / t of oxidant basic unit converted to iron oxide is added. The change of ⁇ P / ⁇ Si in the case is shown.
  • ⁇ P / ⁇ Si increases as dephosphorization proceeds simultaneously with desiliconization.
  • ⁇ P / ⁇ Si is large.
  • the hot metal containing C: 4.50 to 4.70% by mass, Si: 0.50 to 0.60% by mass, and P: 0.100 to 0.120 is particularly preferred in the present invention. It is assumed that it will be the target of the preliminary processing method. In order to preliminarily treat such hot metal and reduce the Si content of the hot metal to 0.2 mass%, in order to produce ultra-low phosphorus steel in the converter process, ⁇ P / ⁇ Si> 0.1 is satisfied. preferable. Therefore, in the method of the present invention, ⁇ P / ⁇ Si> 0.1 was used as an evaluation criterion.
  • the condition necessary for simultaneously proceeding the desiliconization treatment and the dephosphorization treatment is R FeO ⁇ 60%, preferably R FeO ⁇ 70%.
  • the upper limit of R FeO is 100%, but if it exceeds 85%, it is preferable from the viewpoint of securing the required ⁇ P / ⁇ Si, but the reaction efficiency ⁇ 0 of the input oxygen defined by the following formula decreases, so this point is Considering this, R FeO is appropriately set.
  • ⁇ 0 ⁇ ( ⁇ P ⁇ 80/62 + ⁇ Si ⁇ 32/28) ⁇ 1/100 ⁇ / (iron oxide input basic unit ⁇ 1/1000 ⁇ C 0 )
  • iron oxide input basic unit iron oxide input (kg) / molten iron (t);
  • ⁇ P P concentration before pretreatment-P concentration after pretreatment;
  • ⁇ Si Si concentration before pretreatment-Si concentration after pretreatment;
  • C 0 Ratio of oxygen in iron oxide (oxygen mass in iron oxide / total iron oxide mass)
  • the reaction efficiency ⁇ 0 reflects the amount of oxygen reacted with Si and P in the input oxygen.
  • Most of the Si component and the P component in the converter slag are diphosphorus pentoxide (P 2 O 5 ) and silica (SiO 2 ).
  • the amount of oxygen reacted with Si and P in the input oxygen can be calculated from the changes in the P concentration and Si concentration before and after the pretreatment and the amount of iron oxide used in the pretreatment. Therefore, the reaction efficiency ⁇ 0 can be defined from ⁇ P, ⁇ S, and iron oxide input basic unit.
  • the oxidizer basic unit is 25 kg / t, ⁇ P / ⁇ Si decreases, and even when R FeO ⁇ 60%, ⁇ P / ⁇ Si ⁇ 0.1 may be obtained. This is because the oxidizer basic unit is insufficient with respect to the Si concentration of the hot metal, and T.O. It is considered that the Fe concentration was low and the dephosphorization process did not proceed simultaneously with the desiliconization process.
  • the iron oxide to be introduced into the molten iron be 30 kg / t or more in terms of the oxidant basic unit in terms of iron oxide. More preferably, it is 35 kg / t or more.
  • the upper limit of the iron oxide thrown into the hot metal is not particularly limited as long as it is not limited to the scale of equipment for carrying out the pretreatment method of the present invention. If it is a general torpedo car, the upper limit of the iron oxide thrown into the hot metal may be 80 kg / t.
  • the iron oxide to be added to the hot metal is preferably 25 kg / t or more in terms of the oxidizer unit in terms of iron oxide. Is 30 kg / t or more, more preferably 35 kg / t or more, and the ratio R FeO of iron oxide charged from above the hot metal is 60% or more, preferably 70% or more.
  • the ratio R FeO of iron oxide introduced from above the hot metal is preferably 80 to 100%. From the viewpoint of saving labor for the equipment for blowing from the lance 3 into the hot metal 4, the R FeO is preferably 80 to 100%.
  • the conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited.
  • the present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
  • the hot metal discharged from the blast furnace is desiliconized and dephosphorized in the pretreatment step, and then the hot metal in the pretreatment step is refined using a converter to further dephosphorize. .
  • the hot metal discharged from the blast furnace (Si: 0.54% by mass, P: 0.118% by mass, C: 4.6% by mass) is charged into the kneading car, and a lime-based flux and oxidant blowing device is installed. It was transported to a pretreatment plant equipped with it, and hot metal pretreatment (desiliconization treatment and dephosphorization treatment) was performed under various conditions.
  • iron oxide as an oxidizing agent and quicklime as a lime-based flux are blown into the hot metal with a carrier gas (oxygen) from a lance (see FIG. 1).
  • the flow rate is 600 to 800 Nm 3 / hour.
  • a required amount of iron oxide is introduced onto the hot metal from above the kneading vehicle (see FIG. 1).
  • oxygen carrier gas
  • Table 1 shows the results of the hot metal preliminary treatment (desiliconization treatment and dephosphorization treatment).
  • the reaction efficiency ⁇ o of oxygen that contributed to the desiliconization treatment and the dephosphorization treatment is one index for evaluating the efficiency of the hot metal pretreatment.
  • Invention Examples 1 to 6 are examples in which hot metal preliminary treatment (desiliconization treatment and dephosphorization treatment) was performed under the conditions of the present invention.
  • Inventive Examples 1 to 5 are examples in which iron oxide was added in an amount of 35 kg / t of oxidant basic unit in terms of iron oxide, and quick lime was input in an amount of 10 to 20 kg / t of quick lime basic unit.
  • the ratio of iron oxide charged from above the kneading vehicle: R FeO is 70 to 95%.
  • Inventive Examples 1 to 3 satisfy ⁇ P / ⁇ Si> 0.1, and the result of the preliminary treatment is good.
  • [Delta] P / [Delta] Si in Invention Example 3 is higher than [Delta] P / [Delta] Si in Invention Examples 1 and 2, but the efficiency of oxygen that contributes to the desiliconization treatment and the dephosphorization treatment: [eta] o is slightly lower. This is probably because R FeO of Invention Example 3 is as high as 95%, and thus the oxidizing agent blown into the hot metal was insufficient. This shows that R FeO is preferably 60 to 85%.
  • Invention Example 4 is an example in which the quicklime basic unit is changed to 20 kg / t
  • Invention Example 5 is an example in which the quicklime basic unit is changed to 10 kg / t.
  • inventive Example 4 has a higher slag basicity than Inventive Examples 1 to 3
  • Inventive Example 5 has a lower slag basicity than Inventive Examples 1 to 3, but in Inventive Examples 4 and 5, ⁇ P / ⁇ Si There is no major change.
  • the basicity of the inventive example and the comparative example is the mass in terms of SiO 2 of the total amount of silicon used for the hot metal treatment (preliminary treatment in the case of Table 1) and the silicon content contained in the hot metal to be treated.
  • the ratio of the amount of CaO (total (CaO)) used for the hot metal treatment to (total (SiO 2 )) ie, “total (CaO) / total (SiO 2 )”.
  • ⁇ P / Si is as low as 0.05, and a desirable hot metal component composition is not obtained. This is because R FeO is lower than the range of the present invention and the Fe concentration in the slag is low, and the desiliconization reaction proceeds, but the dephosphorization reaction hardly proceeds.
  • the conditions for efficiently carrying out the desiliconization process and the dephosphorization process to make the Si concentration and the P concentration in the hot metal suitable simultaneously are as follows. It was confirmed that the ratio of iron oxide added from above and t FeO was 60% or more. Further, it was confirmed that R FeO is preferably 80 to 100%.
  • Table 2 shows the P concentration after dephosphorization in the refining process using a converter.
  • the amount of gaseous oxygen introduced was 40 to 60 Nm 3 / t in terms of gaseous oxygen intensity.
  • Comparative Examples 1 to 3 are examples in which hot metal having a P content of less than 0.01% could not be produced (example in which “x” was shown in the item “evaluation” in Table 2). In Comparative Examples 1 to 3, the ⁇ P / ⁇ Si of the hot metal after the pretreatment was less than 0.1.
  • Comparative Examples 1 and 3 the P concentration of the hot metal after the pretreatment was more than 0.090 mass%, but the Si concentration of the hot metal after the pretreatment was set to the P concentration in the refining process using a converter. Insufficient to reduce. Therefore, in Comparative Examples 1 and 3, Si was added in a refining process using a converter in order to generate slag containing P in the hot metal. However, in Comparative Examples 1 and 3, since the P concentration of the hot metal after the preliminary treatment was too high, hot metal having a P content of less than 0.01% could not be produced by refining treatment using a converter.
  • the present invention in the hot metal pretreatment, CaF 2 is not used, and the P concentration and Si concentration in the hot metal are appropriately reduced to such an extent that the dephosphorization step after the pretreatment is not hindered. Therefore, ultra-low phosphorus steel can be efficiently melted in the refining process. Therefore, the present invention has high applicability in the steel industry.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
  • Carbon Steel Or Casting Steel Manufacturing (AREA)

Abstract

The present invention provides a molten pig iron pretreatment method for improving the efficiency of dephosphorization without hampering an intermediate slag discharging step in a converter furnace by performing appropriate desiliconization in the molten pig iron pretreatment. This molten pig iron pretreatment method that charges iron oxide, gaseous oxygen and lime-based flux in molten pig iron in a refining vessel to perform desiliconization and dephosphorization, is characterized in that: at least 25 kg/t of iron oxide in oxidizing agent source units calculated as iron oxide are charged and when charging, at least 60% of the charged iron oxide is charged from above the refining vessel; the Si content of the molten pig iron is 0.05–0.30 mass%; and the P content is adjusted to 0.040–0.085 mass%.

Description

溶銑の予備処理方法と極低燐鋼の製造方法Hot metal pretreatment method and ultra low phosphorus steel production method
　本発明は、混銑車において、溶銑のＳｉ濃度及びＰ濃度を効率良く低減する予備処理方法と極低燐鋼の製造方法に関する。 The present invention relates to a pretreatment method for efficiently reducing the Si concentration and the P concentration of molten iron and a method for producing ultra-low phosphorus steel in a kneading vehicle.
　溶銑を転炉で酸素吹錬して溶鋼とする際、転炉での吹錬負荷を低減するとともに、溶鋼を所望の成分組成に調整し易くするため、転炉に装入する溶銑から、予め、珪素、燐、硫黄等を除去する「溶銑予備処理」が、通常行われている。 When the hot metal is blown with oxygen in a converter to form molten steel, in order to reduce the blowing load in the converter and make it easier to adjust the molten steel to the desired component composition, from the hot metal charged in the converter, In general, “hot metal pretreatment” for removing silicon, phosphorus, sulfur and the like is performed.
　例えば、高炉から出銑された溶銑が、まだ、出銑樋、傾注樋、又は、混銑車内に存在する間に、溶銑に、精錬剤として、石灰系フラックス、酸化剤、及び／又は、ソーダ灰系フラックス等を、キャリアガス（例えば、窒素、酸素）で吹き込むか、又は、上方から、直接添加し、珪素、燐、硫黄等をスラグへ移行させて除去する。 For example, while the hot metal discharged from the blast furnace is still present in the ironing, decanting iron, or kneading vehicle, the hot metal, as a refining agent, lime-based flux, oxidizer, and / or soda ash A system flux or the like is blown with a carrier gas (for example, nitrogen or oxygen), or directly added from above, and silicon, phosphorus, sulfur, or the like is transferred to the slag to be removed.
　他方、溶銑予備処理に転炉を用いるプロセス（転炉型溶銑予備処理）も発展を遂げている。転炉型溶銑予備処理は、脱燐用転炉と脱炭用転炉を用いる２炉方式で行うのが一般的であるが、特許文献１には、脱燐処理後に転炉を傾動して脱燐スラグを排滓（中間排滓）し、続いて、脱炭処理を行い、排滓した脱炭スラグを、次の脱燐処理において脱燐剤として再使用する一連の処理工程を１炉で行う方法が提案されている。 On the other hand, a process using a converter for hot metal pretreatment (converter type hot metal pretreatment) has also been developed. The converter type hot metal preliminary treatment is generally performed by a two-furnace system using a dephosphorization converter and a decarburization converter. However, Patent Document 1 discloses that the converter is tilted after the dephosphorization process. A series of treatment steps in which the dephosphorization slag is discharged (intermediate discharge), followed by decarburization, and the decarburized slag is reused as a dephosphorizing agent in the next dephosphorization process in one furnace. The method to do is proposed.
　特許文献１の方法は、１炉方式であることと、脱炭スラグのホットリサイクルによる熱裕度の高さが大きなメリットである。しかし、脱珪・脱燐→中間排滓→脱炭というプロセスにおいて脱珪し過ぎると、主たるスラグ源である珪素（Ｓｉ）の溶銑中の濃度が乏しくなると、中間排滓を行うことが困難になる。このように、脱珪の程度によっては中間排滓が困難になり、中間排滓するために、脱珪が進んだ溶銑にＳｉを添加するか、或いはＳｉＯ２を新たにスラグ源として投入して、溶銑の珪素濃度を再び増加させる等の非経済的な工程が必要になる場合がある。 The method of patent document 1 has a great merit that it is a one-furnace system and a high heat tolerance by hot recycling of decarburized slag. However, if excessive desiliconization is performed in the process of desiliconization / dephosphorization → intermediate exhaustion → decarburization, the concentration of the main slag source silicon (Si) in the molten iron becomes low, making intermediate exhaustion difficult. Become. In this way, depending on the degree of desiliconization, intermediate waste becomes difficult, and in order to carry out intermediate waste, Si is added to the hot metal that has undergone desiliconization, or SiO 2 is newly added as a slag source. In some cases, an uneconomical process such as increasing the silicon concentration of the hot metal again is necessary.
　極低燐鋼を溶製するには、溶銑予備処理により、溶銑のＰ濃度を十分に低減するか、又は、転炉で脱燐処理を施した溶鋼を一旦出鋼し、脱燐スラグの全量を系外へ排出し、同一の転炉で、再度、脱炭及び脱燐吹錬を行うという処理が必要になる。尚、極低燐鋼とは、鋼中の燐含有量が０．０１％以下の鋼である。 In order to produce ultra-low phosphorus steel, the P concentration in the hot metal is sufficiently reduced by the hot metal pretreatment, or the molten steel that has been subjected to dephosphorization treatment in the converter is once removed and the total amount of dephosphorized slag is obtained. Is required to be discharged from the system and decarburized and dephosphorized again in the same converter. The ultra-low phosphorus steel is a steel having a phosphorus content of 0.01% or less.
　転炉にて脱燐処理を施した溶鋼を一旦出鋼し、脱燐スラグの全量を系外へ排出し、同一の転炉で、再度、脱炭及び脱燐吹錬を行う一連の処理は、工程が煩雑で、処理時間が大幅に延長してしまう。このように、特許文献１の方法で超低燐鋼を溶製する場合、工程上の課題が多い。 A series of processes in which molten steel that has been dephosphorized in a converter is once removed, the entire amount of dephosphorization slag is discharged out of the system, and decarburization and dephosphorization blowing are performed again in the same converter. The process is complicated and the processing time is greatly extended. Thus, when melting ultra-low phosphorus steel by the method of Patent Document 1, there are many problems in the process.
　熱力学的に、脱燐反応は、脱珪反応の終了後に進行する。そのため、前述したように溶銑予備処理により溶銑のＰ濃度を十分に低減する場合には、溶銑予備処理において溶銑のＳｉ濃度を略ゼロまで低減する必要がある。 Thermodynamically, the dephosphorization reaction proceeds after completion of the desiliconization reaction. Therefore, when the P concentration of the hot metal is sufficiently reduced by the hot metal pretreatment as described above, it is necessary to reduce the Si concentration of the hot metal to substantially zero in the hot metal pretreatment.
　それ故、従来技術では、極低燐鋼を溶製するため、溶銑予備処理の段階において、溶銑のＰ濃度を規格濃度（Ｐ含有量：０．０１％以下）付近まで低減する必要があった。しかし、極低燐鋼レベルまで脱燐するには、大量のスラグが発生する。トーピードカーにてそのような脱燐を行う場合、トーピードカーのフリーボード（溶銑上に形成される空間の炉口までの高さ）が少ないので、溶銑のＰ濃度を規格濃度付近まで低減することは困難である。 Therefore, in the prior art, it was necessary to reduce the P concentration of the hot metal to the standard concentration (P content: 0.01% or less) in the hot metal preliminary treatment stage in order to produce an extremely low phosphorous steel. . However, a large amount of slag is generated in order to dephosphorize to an extremely low phosphorus steel level. When performing such dephosphorization with a torpedo car, it is difficult to reduce the P concentration in the hot metal to near the standard concentration because the free board of the torpedo car (the height to the furnace opening of the space formed on the hot metal) is small. It is.
　また、従来技術では、混銑車における溶銑予備処理において、脱燐を行う際、形成されるスラグの塩基度が３．０以上となるように石灰系フラックスを吹き込み、かつ、ＣａＯの滓化を促進してフラックス量を減らすため、蛍石（ＣａＦ2）を添加する技術が多用されていた。この技術によれば、ＣａＯの融点が低下し、その滓化が容易になる。 In the prior art, when dephosphorization is performed in the hot metal pretreatment in a kneading vehicle, lime-based flux is blown so that the basicity of the formed slag becomes 3.0 or more, and the hatching of CaO is promoted. In order to reduce the amount of flux, a technique of adding fluorite (CaF 2 ) has been frequently used. According to this technique, the melting point of CaO is lowered and its hatching is facilitated.
　例えば、特許文献２は、以下の条件で、ＣａＯを主に含むフラックスと酸素源を同時に同位置に吹き込むことによって、溶銑からの脱珪と脱燐を同時に進行させる方法を開示する。特許文献２に開示された方法は、蛍石を含有するフラックスを用いて実施されている。
　総酸素供給速度ＶＯ２（Ｎｍ３／ｍｉｎ．Ｔ）≧２．２５［％Ｓｉ］０－０．０３
　但し、［％Ｓｉ］０＝初期［Ｓｉ］濃度 For example, Patent Document 2 discloses a method of simultaneously performing desiliconization and dephosphorization from molten iron by simultaneously blowing a flux mainly containing CaO and an oxygen source into the same position under the following conditions. The method disclosed in Patent Document 2 is carried out using a flux containing fluorite.
Total oxygen supply rate V O2 (Nm 3 /min.T)≧2.25 [% Si] 0 −0.03
However, [% Si] 0 = initial [Si] concentration
　しかし、蛍石（ＣａＦ2）の添加は、形成されるスラグの弗素（Ｆ）濃度を高めることになる。近年、スラグを原料とする土木、建設用資材等から環境への弗素の溶出が問題視されるに及び、環境庁は、スラグ中の弗素についても規制を設けている。また、スラグ中の弗素は、予備処理に使用する容器の耐火物に悪影響を及ぼすので、ない方が好ましい。 However, the addition of fluorite (CaF 2 ) increases the fluorine (F) concentration of the formed slag. In recent years, elution of fluorine into the environment from civil engineering and construction materials using slag as a raw material is regarded as a problem, and the Environment Agency has also established regulations on fluorine in slag. Further, it is preferable that fluorine in the slag does not affect the refractory of the container used for the pretreatment.
　特許文献３には、蛍石を用いず、かつ、脱珪・脱燐を行う溶銑の予備処理方法として、精錬容器内の溶銑に、石灰系フラックス及び酸化剤を吹き込み、脱珪率が９０％になるまでの間に、フラックスの主たる量を溶銑に添加し、スラグの最終塩基度を１．２～２．５にする方法が提案されている。 In Patent Document 3, as a hot metal pretreatment method that does not use fluorite and performs desiliconization and dephosphorization, lime-based flux and an oxidizing agent are blown into hot metal in a refining vessel, and the desiliconization rate is 90%. In the meantime, a method has been proposed in which the main amount of flux is added to the hot metal so that the final basicity of the slag is 1.2 to 2.5.
　しかし、特許文献３の方法では、酸化鉄の添加方法がインジェクション方式であるため、トップスラグのＴ．Ｆｅ（Ｔｏｔａｌ　Ｆｅ）濃度が上昇し難く、脱珪と脱燐が同時に進まず、処理後の溶銑のＳｉ濃度が略ゼロとなるうえ、スラグ量も膨大になってしまう。 However, in the method of Patent Document 3, since the addition method of iron oxide is an injection method, T.S. Fe (Total Fe) concentration is difficult to increase, desiliconization and dephosphorization do not proceed at the same time, the Si concentration in the hot metal after processing becomes substantially zero, and the amount of slag also becomes enormous.
　また、特許文献４は、溶銑保持容器内に保持された溶銑に、その浴面上方から酸化鉄源を添加するとともに、浴面下にＣａＯを主体とする媒溶剤を吹き込むことで溶銑を脱燐処理し、低燐溶銑を製造する方法を開示する。特許文献４に開示された前記方法は、前記酸化鉄源の浴面における投入領域が、面積率で前記媒溶剤の浴面での吹き出し領域の４０％以上とラップするように、前記酸化鉄源を添加することを特徴としている。特許文献４に開示された前記方法は、蛍石等のフッ素源を含む媒溶剤を省略できる。 Patent Document 4 discloses that hot metal held in a hot metal holding container is added with an iron oxide source from above the bath surface, and degassed hot metal by blowing a solvent mainly composed of CaO below the bath surface. Disclosed is a method of treating and producing a low phosphorus hot metal. In the method disclosed in Patent Document 4, the iron oxide source is arranged such that the charging area on the bath surface of the iron oxide source overlaps with 40% or more of the blowing area on the bath surface of the medium solvent in terms of area ratio. It is characterized by adding. The method disclosed in Patent Document 4 can omit a solvent containing a fluorine source such as fluorite.
　特許文献４は、特許文献１の方法と同様に１炉方式であり、中間排滓工程を伴う。特許文献４は、溶銑鍋での脱珪処理により溶銑の珪素濃度を所定のレベルまで低下させた後、生成スラグを排滓することを教示するが、前述した中間排滓工程上の技術的課題を解決する手段を具体的に教示しない。 Patent Document 4 is a one-furnace system similar to the method of Patent Document 1 and involves an intermediate waste process. Patent Document 4 teaches that the generated slag is discharged after the silicon concentration of the hot metal is reduced to a predetermined level by desiliconization treatment in the hot metal ladle. The means for solving this problem is not specifically taught.
特開平０５－２４７５１１号公報Japanese Patent Laid-Open No. 05-247511 特開平０２－９３０１１号公報Japanese Patent Laid-Open No. 02-93011 特開２００１－１５２２２６号公報JP 2001-152226 A 特開２００１－２８８５０７号公報JP 2001-288507 A
　溶銑予備処理を行い、次いで中間排滓を行う場合、特に、特許文献１に開示された１炉方式による脱燐方法を行う場合、脱珪し過ぎると、溶銑中の珪素濃度が乏しくなって中間排滓が困難になるという技術的課題がある。 When hot metal preliminary treatment is performed, and then intermediate waste is performed, particularly when the dephosphorization method using the single furnace method disclosed in Patent Document 1 is performed, if the silicon is excessively desiliconized, the silicon concentration in the hot metal becomes low and intermediate. There is a technical issue that makes it difficult to eliminate.
　また、中間排滓工程を含む溶銑処理方法の場合、脱燐吹錬によって生じた燐濃度の高いスラグを中間排滓工程によって除去しきれずに、前記スラグが中間排滓工程後に残留する。そのため、前述した１炉方式による脱燐方法では、極低燐鋼を溶製することが困難である。 Further, in the case of the hot metal treatment method including the intermediate waste removal process, the slag having a high phosphorus concentration generated by the dephosphorization blowing cannot be completely removed by the intermediate waste removal process, and the slag remains after the intermediate waste removal process. For this reason, it is difficult to melt ultra-low phosphorus steel by the above-mentioned dephosphorization method using a single furnace method.
　そこで、本発明は、従来技術の現状を踏まえ、溶銑の予備処理において、転炉による溶銑処理前に、転炉における中間排滓工程を実施できる程度の珪素濃度を溶銑中に残しつつ、溶銑中のＰ濃度を減らすことによって、製錬工程の脱燐処理及び脱珪処理の効率を向上する予備処理方法と極低燐鋼の溶製方法を提供することを目的とする。 Therefore, the present invention is based on the current state of the art, and in the hot metal preliminary treatment, before the hot metal treatment by the converter, the silicon concentration in the hot metal is left in the hot metal while leaving an intermediate concentration step in the converter. An object of the present invention is to provide a pretreatment method and a method for melting ultra-low phosphorous steel that improve the efficiency of dephosphorization treatment and desiliconization treatment in the smelting process by reducing the P concentration of the steel.
　また、本発明は、溶銑の予備処理において、ＣａＦ2を用いること無く、溶銑のＰ濃度及びＳｉ濃度を効率良く低減することを目的とする。 Another object of the present invention is to efficiently reduce the P concentration and Si concentration of hot metal without using CaF 2 in the hot metal pretreatment.
　本発明者らは、溶銑の予備処理において、脱珪処理及び脱燐処理を同時に進めて溶銑のＳｉ濃度及びＰ濃度を適度に低減できれば、その後の転炉精錬において極低燐鋼の溶製の効率が向上し、精錬工程全体の効率が向上するとの発想のもとで、上記課題を解決する手法について鋭意研究した。 In the hot metal preliminary treatment, the present inventors can proceed with desiliconization treatment and dephosphorization treatment at the same time to appropriately reduce the Si concentration and the P concentration of the hot metal. Based on the idea that efficiency will improve and the efficiency of the entire refining process will improve, we have intensively studied methods for solving the above problems.
　その結果、Ｓｉ含有量が０．０５～０．３０質量％であり、且つＰ含有量が０．０４０～０．０８５質量％になるように溶銑を予備処理することによって、更に転炉等における中間排滓工程と組み合わせることによって、精錬工程全体の効率が向上することが見出された。 As a result, the hot metal is pretreated so that the Si content is 0.05 to 0.30% by mass and the P content is 0.040 to 0.085% by mass. It has been found that the efficiency of the entire refining process is improved by combining with the intermediate waste process.
　また、本発明者らは、溶銑の予備処理において、石灰及び酸化鉄系フラックスによって溶銑の脱珪処理と脱燐処理を同時に行なう際の条件について鋭意研究した。 In addition, the present inventors diligently studied conditions for simultaneously performing desiliconization and dephosphorization of hot metal with lime and iron oxide fluxes in the hot metal pretreatment.
　その結果、予備処理後の溶銑のＳｉ含有量及びＰ含有量を上記範囲にするために、予備処理前後の溶銑のＳｉ含有量及びＰ含有量の変化(ΔP/ΔSi)を０．１超とすることが好ましいことを見出した。 As a result, in order to keep the Si content and the P content of the hot metal after the pretreatment within the above range, the change in the Si content and the P content of the hot metal before and after the pretreatment (ΔP / ΔSi) is more than 0.1. It has been found that it is preferable.
　このように、精錬容器内の溶銑の予備処理において、酸化鉄の投入量、及び、酸化鉄の投入方法を適正化すれば、予備処理後の溶銑のＳｉ濃度及びＰ濃度を、転炉による精錬工程等の次の精錬工程に好適な成分組成に調整できることを見いだした。 In this way, in the pretreatment of the hot metal in the refining vessel, if the amount of iron oxide input and the iron oxide injection method are optimized, the Si concentration and P concentration of the hot metal after the pretreatment are refined by a converter. It has been found that the composition can be adjusted to be suitable for the next refining process such as a process.
　本発明は、上記知見に基づいてなされたもので、その要旨は、次のとおりである。 The present invention has been made on the basis of the above findings, and the gist thereof is as follows.
　（１）精錬容器内の溶銑に、酸化鉄、気体酸素、及び、石灰系フラックスを投入して、脱珪処理と脱燐処理を施す溶銑の予備処理方法において、
　酸化鉄換算の酸化剤原単位で酸化鉄を２５ｋｇ／ｔ以上投入するとともに、
　上記投入の際、投入する酸化鉄の６０％以上を精錬容器の上方から投入して、
　前記溶銑のＳｉ含有量を０．０５～０．３０質量％とし、且つＰ含有量を０．０４０～０．０８５質量％に調整することを特徴とする溶銑の予備処理方法。
　（２）精錬容器内に投入される酸化鉄の全量のうち８０～１００％を精錬容器の上方から投入することを特徴とする（１）に記載の溶銑の予備処理方法。
　（３）予備処理前後のＰ濃度及び予備処理前後のＳｉ濃度が、下記式１を満たすことを特徴とする（１）又は（２）に記載の溶銑の予備処理方法。
　ΔＰ／ΔＳｉ＞０．１・・・（式１）
　但し、ΔＰ：予備処理前Ｐ濃度と予備処理後Ｐ濃度との差、ΔＳｉ：予備処理前Ｓｉ濃度と予備処理後Ｓｉ濃度との差
　（４）石灰系フラックスは、ＣａＦ2を含有しないことを特徴とする（１）～（３）のうちいずれかに記載の溶銑の予備処理方法。
　（５）前記精錬容器が混銑車であることを特徴とする（１）～（４）のうちいずれかに記載の溶銑の予備処理方法。
　（６）（１）～（５）のうちいずれかに記載の予備処理方法後に、転炉での中間排滓を行うことを特徴とする極低燐鋼の製造方法。 (1) In the hot metal pretreatment method in which iron oxide, gaseous oxygen, and lime-based flux are introduced into the hot metal in the refining vessel, and desiliconization treatment and dephosphorization treatment are performed.
In addition to adding 25 kg / t or more of iron oxide in terms of oxidant unit in terms of iron oxide,
At the time of the above charging, 60% or more of the iron oxide to be charged is charged from above the refining vessel,
A hot metal preliminary treatment method, wherein the Si content of the hot metal is adjusted to 0.05 to 0.30 mass% and the P content is adjusted to 0.040 to 0.085 mass%.
(2) The hot metal preliminary treatment method according to (1), wherein 80 to 100% of the total amount of iron oxide charged into the refining vessel is charged from above the refining vessel.
(3) The hot metal pretreatment method according to (1) or (2), wherein the P concentration before and after the pretreatment and the Si concentration before and after the pretreatment satisfy the following formula 1.
ΔP / ΔSi> 0.1 (Expression 1)
However, ΔP: difference between P concentration before pretreatment and P concentration after pretreatment, ΔSi: difference between Si concentration before pretreatment and Si concentration after pretreatment (4) The lime-based flux does not contain CaF 2 The hot metal pretreatment method according to any one of (1) to (3), which is characterized in that
(5) The hot metal pretreatment method according to any one of (1) to (4), wherein the smelting vessel is a chaotic vehicle.
(6) A method for producing ultra-low phosphorus steel, characterized in that after the pretreatment method according to any one of (1) to (5), intermediate waste in a converter is performed.
　本発明によれば、転炉での中間排滓工程を妨げないように予備処理を行うことができるので、本発明の予備処理方法を利用することによって、転炉による精錬工程において極低燐鋼を効率良く溶製できる。 According to the present invention, since the preliminary treatment can be performed so as not to interfere with the intermediate waste process in the converter, by using the preliminary treatment method of the present invention, an extremely low phosphorus steel in the refining process by the converter. Can be efficiently melted.
　また、本発明によれば、溶銑の予備処理において、ＣａＦ2を用いること無く、溶銑のＰ濃度及びＳｉ濃度を効率良く低減することができる。 According to the present invention, the hot metal P concentration and Si concentration can be efficiently reduced without using CaF 2 in the hot metal pretreatment.
混銑車を精錬容器として使用する溶銑の予備処理の一態様を模式的に示す図である。It is a figure which shows typically the one aspect | mode of the hot metal pre-processing which uses a kneading vehicle as a refining container. 混銑車の上方から投入する酸化鉄の割合：ＲFeO（％）と、予備処理前後でのＰ濃度の変化量（質量％）ΔＰとＳｉ濃度の変化量（質量％）ΔＳｉの比：ΔＰ／ΔＳｉの関係を示す図である。Ratio of iron oxide thrown from above the kneading wheel: R FeO (%), and ratio of change in P concentration (mass%) ΔP and change in Si concentration (mass%) ΔSi before and after the pretreatment: ΔP / It is a figure which shows the relationship of (DELTA) Si.
　本発明の溶銑の予備処理方法（以下「本発明方法」ということがある。）は、精錬容器内の溶銑に、酸化鉄、気体酸素、及び、石灰系フラックスを投入して、脱珪処理と脱燐処理を施す溶銑の予備処理方法において、
　（ｉ）酸化鉄を、酸化鉄換算の酸化剤原単位で２５ｋｇ／ｔ以上を投入するとともに、
　（ii）上記投入の際、投入する酸化鉄の６０％以上を精錬容器の上方から投入し、
　（iii）溶銑のＳｉ含有量を０．０５～０．３０質量％とし、且つＰ含有量を０．０４０～０．０８５質量％に調整する
ことを特徴とする。 The hot metal pretreatment method of the present invention (hereinafter also referred to as “the present invention method”) is a method of desiliconization by introducing iron oxide, gaseous oxygen, and lime-based flux into the hot metal in the refining vessel. In the hot metal pretreatment method for dephosphorization,
(I) While adding 25 kg / t or more of iron oxide in terms of iron oxide equivalent oxidizer basic unit,
(Ii) At the time of the above charging, 60% or more of the iron oxide to be charged is charged from above the refining vessel,
(Iii) The hot metal has a Si content of 0.05 to 0.30 mass% and a P content of 0.040 to 0.085 mass%.
　以下、本発明方法について説明する。 Hereinafter, the method of the present invention will be described.
　本発明の予備処理方法の対象とする溶銑は、Ｓｉ：０．８０質量％以下、Ｐ：１．２００質量％以下であれば、特定の成分組成に限定されず、通常の成分組成の溶銑である具体的には、例えば、高炉から出銑した溶銑や、電気炉で溶解した溶銑が挙げられる。 As long as the hot metal targeted for the pretreatment method of the present invention is Si: 0.80 mass% or less and P: 1.200 mass% or less, the hot metal is not limited to a specific component composition, but is a hot metal having a normal component composition. Specifically, for example, hot metal discharged from a blast furnace and hot metal melted in an electric furnace can be used.
　溶銑の予備処理は、溶銑を精錬工程へ搬送するのに主として使用する混銑車を精錬容器として使用して行うので、混銑車を精錬容器として使用する溶銑の予備処理について説明するが、精錬容器は、混銑車に限らず、溶銑を、次の精錬工程へ搬送するための容器（例えば、溶銑鍋等）であって、予備精錬を行うことが可能な容器であればよい。 Since the hot metal pretreatment is performed using a kneading vehicle mainly used to transport the hot metal to the refining process as a refining vessel, the pretreatment of hot metal using the kneading vehicle as a refining vessel will be described. The container is not limited to a kneading vehicle, and may be a container (for example, a hot metal ladle or the like) for transporting hot metal to the next refining process and capable of performing preliminary refining.
　図１に、混銑車を精錬容器として使用する溶銑の予備処理の一態様を模式的に示す。図１に示すように、混銑車１の開口部２からランス３を溶銑４中に浸漬し、石灰系フラックス５及び／又は酸化剤６（酸化鉄）を、キャリアガス７（気体酸素）で搬送し、所要の時間、ランス３から溶銑４中に吹き込む。 FIG. 1 schematically shows an embodiment of hot metal pretreatment using a kneading vehicle as a refining vessel. As shown in FIG. 1, the lance 3 is immersed in the hot metal 4 from the opening 2 of the kneading wheel 1, and the lime-based flux 5 and / or the oxidizing agent 6 (iron oxide) is conveyed by the carrier gas 7 (gaseous oxygen). Then, blow into the hot metal 4 from the lance 3 for the required time.
　溶銑４中のＳｉ及びＰは、酸化されてスラグ８に移行し、溶銑４の予備処理（脱珪処理と脱燐処理）が進行する。例えば、溶銑のＳｉ濃度が、０．０５～０．３０質量％に達した時、予備処理を中断して混銑車１を傾転し、生成したスラグ８を混銑車１外へ排出する。次いで、石灰系フラックス５と酸化剤６で予備処理を再開する。 Si and P in the hot metal 4 are oxidized and transferred to the slag 8, and the pretreatment (desiliconization and dephosphorization) of the hot metal 4 proceeds. For example, when the Si concentration of the hot metal reaches 0.05 to 0.30 mass%, the pretreatment is interrupted, the kneading vehicle 1 is tilted, and the generated slag 8 is discharged out of the kneading vehicle 1. Next, the pretreatment is restarted with the lime-based flux 5 and the oxidizing agent 6.
　本発明方法は、溶銑の予備処理（脱珪処理と脱燐処理）において、酸化剤として酸化鉄を溶銑に投入する際、投入する酸化鉄の６０％以上の酸化鉄６ａを、混銑車の上方から、即ち、開口部２に配置したシュート９から溶銑４に投入する。 In the method of the present invention, when iron oxide is added as an oxidizing agent to hot metal in the hot metal pretreatment (desiliconization treatment and dephosphorization treatment), iron oxide 6a of 60% or more of the iron oxide to be added is From the chute 9 disposed in the opening 2.
　酸化鉄源は、例えば、ミルスケール、焼結鉱、鉄鉱石、焼結ダスト等である。石灰系フラックスは、ＣａＯ単独でもよく、主成分をＣａＯとする、炭酸カルシウム（ＣａＣＯ3）や、転炉滓等の混合物でもよい。但し、前述したように、外部環境及び予備処理に使用する容器の耐火物への悪影響を考慮して、蛍石を用いないことが好ましい。 Examples of the iron oxide source include mill scale, sintered ore, iron ore, and sintered dust. The lime-based flux may be CaO alone, or may be a mixture of calcium carbonate (CaCO 3 ) or a converter soot whose main component is CaO. However, as described above, it is preferable not to use fluorite in consideration of the adverse effect on the refractory of the container used for the external environment and pretreatment.
　本発明方法において、酸化鉄を、酸化鉄換算の酸化剤原単位で２５ｋｇ／ｔ以上を、溶銑に投入するが、この点については後述する。なお、酸化鉄の投入量は、混銑車に装入した溶銑に投入した酸化鉄の合計質量である。また、「酸化鉄換算の酸化剤原単位」とは、溶銑予備処理工程において、溶銑１ｔを予備処理するために投入した酸素の全質量を、ＦｅＯに換算した質量である。 In the method of the present invention, 25 kg / t or more of iron oxide in terms of iron oxide-converted oxidant basic unit is charged into the hot metal, which will be described later. The input amount of iron oxide is the total mass of iron oxide charged into the hot metal charged in the kneading vehicle. In addition, the “oxidizing agent basic unit in terms of iron oxide” is a mass obtained by converting the total mass of oxygen supplied for pretreatment of hot metal 1t into FeO in the hot metal pretreatment process.
　脱珪反応と同時に脱燐反応を進めるためには、溶銑のＳｉ活量を下げつつ、溶銑とスラグの反応界面における酸素ポテンシャルを高める必要がある。酸化鉄を、上方から投入することで、スラグのＦｅ濃度を高く保つことができると考えられるが、上方添加は、溶銑への直接吹込みに比べて反応効率が低いので、単に、酸化鉄の全量を上方添加しても、反応効率が低下するばかりで、脱珪処理も脱燐処理も不十分になってしまう。 To advance the dephosphorization reaction simultaneously with the desiliconization reaction, it is necessary to increase the oxygen potential at the reaction interface between the hot metal and the slag while lowering the Si activity of the hot metal. It is thought that the Fe concentration in the slag can be kept high by adding iron oxide from above, but since the addition efficiency of the upward addition is lower than direct blowing into the hot metal, Even if the total amount is added upward, the reaction efficiency is lowered, and the desiliconization treatment and the dephosphorization treatment become insufficient.
　したがって、溶銑の予備処理において、脱珪効率と脱燐効率をともに最大化するためには、酸化鉄を、酸化剤原単位でどの程度投入し、また、どの程度の割合で上方添加すべきかを明らかにする必要があるが、従来、溶銑への酸化鉄の投入に関する定量的な検討、考察はなされておらず、当然に、定量的な指針は示されていない。 Therefore, in order to maximize both the desiliconization efficiency and the dephosphorization efficiency in the hot metal pretreatment, how much iron oxide should be added in terms of the oxidizer basic unit and at what rate should be added upward. Although it is necessary to clarify, conventionally, quantitative examination and consideration regarding the input of iron oxide into hot metal have not been made, and naturally no quantitative guideline has been shown.
　本発明者らは、溶銑への酸化鉄の投入に関し、定量的な検討を鋭意行い、溶銑に投入する酸化鉄の酸化鉄換算の酸化剤原単位、及び、溶銑の上方から投入すべき酸化鉄の割合（％）を明らかにした。 The present inventors diligently conducted quantitative investigations regarding the addition of iron oxide to hot metal, and the iron oxide equivalent oxidizer unit of iron oxide to be added to hot metal, and the iron oxide to be supplied from above the hot metal The percentage (%) was clarified.
　図２に、混銑車の上方から投入する酸化鉄の割合：ＲFeO（％）と、予備処理前後でのＰ濃度の変化量（質量％）ΔＰとＳｉ濃度の変化量（質量％）ΔＳｉの比：ΔＰ／ΔＳｉの関係を示す。図２には、溶銑に酸化鉄を、酸化鉄換算の酸化剤原単位で３５ｋｇ／ｔを投入した場合のΔＰ／ΔＳｉの変化と、酸化鉄換算の酸化剤原単位で２５ｋｇ／ｔを投入した場合のΔＰ／ΔＳｉの変化を示す。 FIG. 2 shows the ratio of iron oxide introduced from above the kneading vehicle: R FeO (%), the amount of change in P concentration (mass%) ΔP and the amount of change in Si concentration (mass%) ΔSi before and after the pretreatment. Ratio: A relationship of ΔP / ΔSi is shown. FIG. 2 shows changes in ΔP / ΔSi when iron oxide is added to the hot metal, and 35 kg / t of oxidant basic unit converted to iron oxide, and 25 kg / t of oxidant basic unit converted to iron oxide is added. The change of ΔP / ΔSi in the case is shown.
　脱珪と同時に脱燐が進行するほど、ΔＰ／ΔＳｉは大きくなる。転炉工程にて極低燐鋼を溶製するには、Ｓｉをある程度残しつつ、Ｐをできるだけ除去することが望ましいため、ΔＰ／ΔＳｉが大きい方が好ましい。 ΔP / ΔSi increases as dephosphorization proceeds simultaneously with desiliconization. In order to melt the ultra-low phosphor steel in the converter process, it is desirable to remove P as much as possible while leaving a certain amount of Si. Therefore, it is preferable that ΔP / ΔSi is large.
　前述した溶銑のうち、Ｃ：４．５０～４．７０質量％、Ｓｉ：０．５０～０．６０質量％、Ｐ：０．１００～０．１２０を含有する溶銑が、特に、本発明の予備処理方法の対象になると想定される。このような溶銑を予備処理して当該溶銑のＳｉ含有量を０．２質量％まで低減した後、転炉工程にて極低燐鋼を溶製するには、ΔＰ／ΔＳｉ＞０．１が好ましい。そこで、本発明方法では、ΔＰ／ΔＳｉ＞０．１を評価基準とした。 Among the aforementioned hot metal, the hot metal containing C: 4.50 to 4.70% by mass, Si: 0.50 to 0.60% by mass, and P: 0.100 to 0.120 is particularly preferred in the present invention. It is assumed that it will be the target of the preliminary processing method. In order to preliminarily treat such hot metal and reduce the Si content of the hot metal to 0.2 mass%, in order to produce ultra-low phosphorus steel in the converter process, ΔP / ΔSi> 0.1 is satisfied. preferable. Therefore, in the method of the present invention, ΔP / ΔSi> 0.1 was used as an evaluation criterion.
　ＲFeO（％）の増加に伴い、ΔＰ／ΔＳｉも増加し、酸化剤原単位が３５ｋｇ／ｔの場合、ＲFeO＝６０％で、ΔＰ／ΔＳｉ＞０．１となり、ＲFeO≧７０％では、RFeOが増加し、ΔＰ／ΔＳｉは０．１４～０．１８である。 As R FeO (%) increases, ΔP / ΔSi also increases. When the oxidizer basic unit is 35 kg / t, R FeO = 60%, ΔP / ΔSi> 0.1, and R FeO ≧ 70%. R FeO increases, and ΔP / ΔSi is 0.14 to 0.18.
　このことから、脱珪処理と脱燐処理を同時に進めるのに必要な条件は、ＲFeO≧６０％であり、好ましくはＲFeO≧７０％である。ＲFeOの上限は１００％であるが、８５％を超えると、所要のΔＰ／ΔＳｉの確保の点で好ましいが、下記式で定義する投入酸素の反応効率η0が低下するので、この点を考慮して、ＲFeOを適宜設定する。 For this reason, the condition necessary for simultaneously proceeding the desiliconization treatment and the dephosphorization treatment is R FeO ≧ 60%, preferably R FeO ≧ 70%. The upper limit of R FeO is 100%, but if it exceeds 85%, it is preferable from the viewpoint of securing the required ΔP / ΔSi, but the reaction efficiency η 0 of the input oxygen defined by the following formula decreases, so this point is Considering this, R FeO is appropriately set.
　　η0＝｛（ΔＰ×80／62＋ΔＳｉ×32／28）×1/100｝／（酸化鉄投入量原単位×1/1000×Ｃ0）
　ここで、酸化鉄投入量原単位：酸化鉄投入量（ｋｇ）／溶銑量（ｔ）；
　　　　　ΔＰ：予備処理前Ｐ濃度－予備処理後Ｐ濃度；
　　　　　ΔＳｉ：予備処理前Ｓｉ濃度－予備処理後Ｓｉ濃度；
　　　　　Ｃ0：酸化鉄中の酸素の割合（酸化鉄中の酸素質量／酸化鉄総質量） η 0 = {(ΔP × 80/62 + ΔSi × 32/28) × 1/100} / (iron oxide input basic unit × 1/1000 × C 0 )
Here, iron oxide input basic unit: iron oxide input (kg) / molten iron (t);
ΔP: P concentration before pretreatment-P concentration after pretreatment;
ΔSi: Si concentration before pretreatment-Si concentration after pretreatment;
C 0 : Ratio of oxygen in iron oxide (oxygen mass in iron oxide / total iron oxide mass)
　前記反応効率η0は、投入酸素のうちＳｉ及びＰと反応した酸素量を反映する。転炉スラグ中のＳｉ成分及びＰ成分は、殆どが、五酸化二燐（Ｐ２Ｏ５）及びシリカ（ＳｉＯ２）である。投入酸素のうちＳｉ及びＰと反応した酸素量は、予備処理前後のＰ濃度及びＳｉ濃度の変化と、予備処理に使用された酸化鉄量から算出することができる。従って、前記反応効率η0は、ΔＰ、ΔＳ及び酸化鉄投入量原単位から定義することができる。 The reaction efficiency η 0 reflects the amount of oxygen reacted with Si and P in the input oxygen. Most of the Si component and the P component in the converter slag are diphosphorus pentoxide (P 2 O 5 ) and silica (SiO 2 ). The amount of oxygen reacted with Si and P in the input oxygen can be calculated from the changes in the P concentration and Si concentration before and after the pretreatment and the amount of iron oxide used in the pretreatment. Therefore, the reaction efficiency η 0 can be defined from ΔP, ΔS, and iron oxide input basic unit.
　酸化剤原単位が２５ｋｇ／ｔの場合、ΔＰ／ΔＳｉは低下し、ＲFeO≧６０％でも、ΔＰ／ΔＳｉ＜０．１となる場合がある。これは、溶銑のＳｉ濃度に対して酸化剤原単位が不足し、余剰酸素源のスラグ中のＴ．Ｆｅの濃度が低位となり、脱珪処理と同時に脱燐処理が進行しなかったと考えられる。 When the oxidizer basic unit is 25 kg / t, ΔP / ΔSi decreases, and even when R FeO ≧ 60%, ΔP / ΔSi <0.1 may be obtained. This is because the oxidizer basic unit is insufficient with respect to the Si concentration of the hot metal, and T.O. It is considered that the Fe concentration was low and the dephosphorization process did not proceed simultaneously with the desiliconization process.
　本発明方法では、図２に示す結果を踏まえ、溶銑に投入する酸化鉄は、酸化鉄換算の酸化剤原単位で３０ｋｇ／ｔ以上とすることが好ましい。更に好ましくは３５ｋｇ／ｔ以上である。尚、溶銑に投入する酸化鉄の上限は、本発明の予備処理方法を実施するための設備の規模に制限されない限り、特に限定されない。一般的なトーピードカーであれば、溶銑に投入する酸化鉄の上限を８０ｋｇ／ｔとしても良い。 In the method of the present invention, based on the result shown in FIG. 2, it is preferable that the iron oxide to be introduced into the molten iron be 30 kg / t or more in terms of the oxidant basic unit in terms of iron oxide. More preferably, it is 35 kg / t or more. In addition, the upper limit of the iron oxide thrown into the hot metal is not particularly limited as long as it is not limited to the scale of equipment for carrying out the pretreatment method of the present invention. If it is a general torpedo car, the upper limit of the iron oxide thrown into the hot metal may be 80 kg / t.
　このように、溶銑の予備処理において、脱珪処理と脱燐処理を同時に効率良く進めるための条件は、溶銑に投入する酸化鉄が、酸化鉄換算の酸化剤原単位で２５ｋｇ／ｔ以上、好ましくは３０ｋｇ／ｔ以上、更に好ましくは３５ｋｇ／ｔ以上で、かつ、溶銑の上方から投入する酸化鉄の割合ＲFeOが６０％以上、好ましくは７０％以上である。 As described above, in the hot metal pretreatment, the conditions for efficiently proceeding with the desiliconization treatment and the dephosphorization treatment are as follows. The iron oxide to be added to the hot metal is preferably 25 kg / t or more in terms of the oxidizer unit in terms of iron oxide. Is 30 kg / t or more, more preferably 35 kg / t or more, and the ratio R FeO of iron oxide charged from above the hot metal is 60% or more, preferably 70% or more.
　特に、溶銑の上方から投入する酸化鉄の割合ＲFeOは、８０～１００％であることが好ましい。ランス３から溶銑４中に吹き込むための設備を省力化する観点からも、前記ＲFeOを８０～１００％とすることが好ましい。 In particular, the ratio R FeO of iron oxide introduced from above the hot metal is preferably 80 to 100%. From the viewpoint of saving labor for the equipment for blowing from the lance 3 into the hot metal 4, the R FeO is preferably 80 to 100%.
　次に、本発明の実施例について説明するが、実施例での条件は、本発明の実施可能性及び効果を確認するために採用した一条件例であり、本発明は、この一条件例に限定されるものではない。本発明は、本発明の要旨を逸脱せず、本発明の目的を達成する限りにおいて、種々の条件を採用し得るものである。尚、以下の実施例では、高炉から出銑した溶銑を予備処理工程にて脱珪及び脱燐し、次いで、転炉を用いて予備処理工程の溶銑を精錬して更に脱燐を行っている。 Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention. In the following examples, the hot metal discharged from the blast furnace is desiliconized and dephosphorized in the pretreatment step, and then the hot metal in the pretreatment step is refined using a converter to further dephosphorize. .
［溶銑の予備処理工程］
　高炉から出銑した溶銑（Ｓｉ：０．５４質量％、Ｐ：０．１１８質量％、Ｃ：４．６質量％）を混銑車に装入し、石灰系フラックスと酸化剤の吹込み装置を備える予備処理場へ搬送し、種々の条件の下で、溶銑の予備処理（脱珪処理と脱燐処理）を実施した。 [Pretreatment process of hot metal]
The hot metal discharged from the blast furnace (Si: 0.54% by mass, P: 0.118% by mass, C: 4.6% by mass) is charged into the kneading car, and a lime-based flux and oxidant blowing device is installed. It was transported to a pretreatment plant equipped with it, and hot metal pretreatment (desiliconization treatment and dephosphorization treatment) was performed under various conditions.
　それぞれの条件で５チャージ実施し、平均値を算出した。１チャージで、混銑車に装入した溶銑は２６０～２８０トンである。予備処理（脱珪処理と脱燐処理）の手順は以下のとおりである。 * 5 charges were carried out under each condition, and the average value was calculated. The hot metal charged in the chaotic car with one charge is 260-280 tons. The procedure of preliminary treatment (desiliconization treatment and dephosphorization treatment) is as follows.
　まず、溶銑中へ、ランスから、酸化剤としての酸化鉄と石灰系フラックスとしての生石灰をキャリアガス（酸素）で吹き込む（図１、参照）。その流量は６００～８００Ｎｍ3／時間である。吹込みと同時に、混銑車の上方から、溶銑上に、所要量の酸化鉄を投入する（図１、参照）。混銑車の上方から酸化鉄を投入した後、酸化鉄及び生石灰の吹込み、及び、酸素（キャリアガス）の吹込みを継続して、溶銑を撹拌し、２０～３０分経過後に予備処理を終了する。 First, iron oxide as an oxidizing agent and quicklime as a lime-based flux are blown into the hot metal with a carrier gas (oxygen) from a lance (see FIG. 1). The flow rate is 600 to 800 Nm 3 / hour. Simultaneously with the blowing, a required amount of iron oxide is introduced onto the hot metal from above the kneading vehicle (see FIG. 1). After iron oxide is added from above the kneading car, iron oxide and quicklime are blown in, and oxygen (carrier gas) is blown in continuously to agitate the hot metal, and the pretreatment is completed after 20 to 30 minutes. To do.
　表１に、溶銑の予備処理（脱珪処理と脱燐処理）の結果を示す。表１中、脱珪処理と脱燐処理に寄与した酸素の反応効率ηo（上記定義式、参照）は、溶銑の予備処理の効率を評価する一つの指標である。 Table 1 shows the results of the hot metal preliminary treatment (desiliconization treatment and dephosphorization treatment). In Table 1, the reaction efficiency ηo of oxygen that contributed to the desiliconization treatment and the dephosphorization treatment (see the above-mentioned definition formula) is one index for evaluating the efficiency of the hot metal pretreatment.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　発明例１～６は、本発明の条件で、溶銑の予備処理（脱珪処理と脱燐処理）を実施した例である。発明例１～５は、酸化鉄を、酸化鉄換算の酸化剤原単位で３５ｋｇ／ｔ、生石灰を、生石灰原単位で１０～２０ｋｇ／ｔ投入した例である。発明例１～５において、混銑車の上方から投入した酸化鉄の割合：ＲFeOは７０～９５％である。 Invention Examples 1 to 6 are examples in which hot metal preliminary treatment (desiliconization treatment and dephosphorization treatment) was performed under the conditions of the present invention. Inventive Examples 1 to 5 are examples in which iron oxide was added in an amount of 35 kg / t of oxidant basic unit in terms of iron oxide, and quick lime was input in an amount of 10 to 20 kg / t of quick lime basic unit. In Invention Examples 1 to 5, the ratio of iron oxide charged from above the kneading vehicle: R FeO is 70 to 95%.
　発明例１～３は、ΔＰ／ΔＳｉ＞０．１を満足していて、予備処理の結果は良好である。発明例３のΔＰ／ΔＳｉは、発明例１及び２のΔＰ／ΔＳｉより高位であるが、脱珪処理と脱燐処理に寄与した酸素の効率：ηoがやや低位である。これは、発明例３のＲFeOが９５％と高位であるため、溶銑中に吹き込まれる酸化剤が不足したためと考えられる。このことから、ＲFeOは、６０～８５％が好ましいことが分かる。 Inventive Examples 1 to 3 satisfy ΔP / ΔSi> 0.1, and the result of the preliminary treatment is good. [Delta] P / [Delta] Si in Invention Example 3 is higher than [Delta] P / [Delta] Si in Invention Examples 1 and 2, but the efficiency of oxygen that contributes to the desiliconization treatment and the dephosphorization treatment: [eta] o is slightly lower. This is probably because R FeO of Invention Example 3 is as high as 95%, and thus the oxidizing agent blown into the hot metal was insufficient. This shows that R FeO is preferably 60 to 85%.
　発明例４は、生石灰原単位を２０ｋｇ／ｔに変更した例であり、発明例５は、生石灰原単位を１０ｋｇ／ｔに変更した例である。発明例４は、スラグの塩基度が発明例１～３より高く、発明例５は、スラグの塩基度が発明例１～３より低いが、発明例４及び発明例５において、ΔＰ／ΔＳｉに大きな変化はみられない。尚、発明例及び比較例の塩基度は、溶銑の処理（表１の場合、予備処理）のために使用した珪素量及び処理対象の溶銑に含有される珪素量の合計のＳｉＯ２換算の質量（ｔｏｔａｌ（ＳｉＯ２））に対する、溶銑の処理のために使用したＣａＯ量（ｔｏｔａｌ（ＣａＯ））の割合（すなわち、「ｔｏｔａｌ（ＣａＯ）／ｔｏｔａｌ（ＳｉＯ２）」である。 Invention Example 4 is an example in which the quicklime basic unit is changed to 20 kg / t, and Invention Example 5 is an example in which the quicklime basic unit is changed to 10 kg / t. Inventive Example 4 has a higher slag basicity than Inventive Examples 1 to 3, and Inventive Example 5 has a lower slag basicity than Inventive Examples 1 to 3, but in Inventive Examples 4 and 5, ΔP / ΔSi There is no major change. The basicity of the inventive example and the comparative example is the mass in terms of SiO 2 of the total amount of silicon used for the hot metal treatment (preliminary treatment in the case of Table 1) and the silicon content contained in the hot metal to be treated. The ratio of the amount of CaO (total (CaO)) used for the hot metal treatment to (total (SiO 2 )) (ie, “total (CaO) / total (SiO 2 )”).
　発明例６は、酸化鉄換算の酸化剤原単位は３１ｋｇ／ｔ、生石灰原単位は１５ｋｇ／ｔ、上方から投入した酸化鉄の割合：ＲFeOは６５％の例である。ΔＰ／ΔＳｉ＝０．１３で、ΔＰ／ΔＳｉ＞０．１を満足しており、予備処理の結果は良好である。 Invention Example 6 is an example in which the oxidizer unit in terms of iron oxide is 31 kg / t, the quicklime unit is 15 kg / t, and the ratio of iron oxide charged from above: R FeO is 65%. ΔP / ΔSi = 0.13 and ΔP / ΔSi> 0.1 are satisfied, and the result of the preliminary treatment is good.
　比較例１は、ＲFeO＝３０％、酸化剤原単位４３ｋｇ／ｔ、生石灰原単位１５ｋｇ／ｔの条件で予備処理を実施した例である。ΔＰ／Ｓｉが０．０５と低く、望ましい溶銑の成分組成が得られていない。これは、ＲFeOが本発明の範囲より低くて、スラグのＦｅ濃度が低く、脱珪反応は進行したが、脱燐反応は殆ど進行しなかったためである。 Comparative Example 1 is an example in which pretreatment was performed under the conditions of R FeO = 30%, oxidizer basic unit 43 kg / t, and quicklime basic unit 15 kg / t. ΔP / Si is as low as 0.05, and a desirable hot metal component composition is not obtained. This is because R FeO is lower than the range of the present invention and the Fe concentration in the slag is low, and the desiliconization reaction proceeds, but the dephosphorization reaction hardly proceeds.
　比較例２は、ＲFeO＝６５％、酸化剤原単位２５ｋｇ／ｔ、生石灰原単位１５ｋｇ／ｔの例である。ΔＰ／ΔＳｉは０．０９で、比較例１より高位であるが、発明例に比べ低位である。これは、溶銑のＳｉ濃度に対して酸化剤原単位が不足し、余剰酸素源のスラグ中のＴ．Ｆｅ（全鉄）の濃度が低位で、脱珪処理と同時に脱燐処理が進行しなかったと考えられる。 Comparative Example 2 is an example in which R FeO = 65%, oxidizer basic unit 25 kg / t, and quicklime basic unit 15 kg / t. ΔP / ΔSi is 0.09, which is higher than that of Comparative Example 1, but lower than that of the inventive example. This is because the oxidizer basic unit is insufficient with respect to the Si concentration of the hot metal, and T.O. It is considered that the concentration of Fe (total iron) was low and the dephosphorization process did not proceed simultaneously with the desiliconization process.
　以上、溶銑の予備処理において、溶銑中のＳｉ濃度及びＰ濃度を適切にする脱珪処理と脱燐処理を、同時に、効率良く進めるための条件は、酸化鉄換算の酸化剤原単位が２５ｋｇ／ｔ以上、かつ、上方から投入する酸化鉄の割合：ＲFeOが６０％以上であることを確認できた。また、ＲFeOは、８０～１００％が好ましいことを確認できた。 As described above, in the pretreatment of hot metal, the conditions for efficiently carrying out the desiliconization process and the dephosphorization process to make the Si concentration and the P concentration in the hot metal suitable simultaneously are as follows. It was confirmed that the ratio of iron oxide added from above and t FeO was 60% or more. Further, it was confirmed that R FeO is preferably 80 to 100%.
［転炉を用いた精錬工程］
　前述の予備処理後、発明例１～９及び比較例１～３の溶銑のそれぞれの溶銑を表２の条件にて精錬して、極低燐鋼の製造を試みた。 [Refining process using a converter]
After the preliminary treatment described above, the hot metal of Invention Examples 1 to 9 and Comparative Examples 1 to 3 was refined under the conditions shown in Table 2 to try to produce ultra-low phosphorus steel.
　まず、発明例１～９及び比較例１～３の各溶銑に、表２の条件にて石灰系フラックスとして生石灰をキャリアガス（窒素ガス）とともに転炉の底吹きノズルから転炉内の溶銑中に吹き込み、気体酸素を溶銑の液面に吹き付けた。 First, in each hot metal of Invention Examples 1 to 9 and Comparative Examples 1 to 3, quick lime was added as a lime-based flux under the conditions shown in Table 2 together with a carrier gas (nitrogen gas) from the bottom blowing nozzle of the converter into the hot metal in the converter. Then, gaseous oxygen was blown onto the liquid surface of the hot metal.
　前記石灰系フラックスを転炉内に投入後、中間排滓を行ってスラグを廃棄した。中間排滓前の脱燐吹錬時のスラグの塩基度は、１．５～２．０であった。その後、更に、気体酸素を溶銑中に吹き込み、溶銑を撹拌し、１５～２０分経過後に転炉を用いた精錬工程を終了した。中間排滓後の脱炭素吹錬時のスラグの塩基度は、３．０～３．５であった。 After putting the lime-based flux into the converter, intermediate slag was performed and slag was discarded. The basicity of the slag at the time of dephosphorization before intermediate waste was 1.5 to 2.0. Thereafter, gaseous oxygen was further blown into the hot metal, and the hot metal was stirred. After 15 to 20 minutes, the refining process using the converter was completed. The basicity of the slag at the time of decarbonization blowing after the intermediate evacuation was 3.0 to 3.5.
　転炉を用いた精錬工程において、脱燐後のＰ濃度を表２に示す。尚、気体酸素の投入量は、気体酸素原単位で４０～６０Nm3/tであった。 Table 2 shows the P concentration after dephosphorization in the refining process using a converter. The amount of gaseous oxygen introduced was 40 to 60 Nm 3 / t in terms of gaseous oxygen intensity.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　極低燐鋼を製造できた例を合格の実施例とした（表２の項目「評価」において“○”又は“△”が示された例）。特に、前記合格の実施例のうち、Ｓｉ添加が不要な例を“○”で示した。発明例１～９において、Ｐ含有量が０．０１％未満の溶銑を製造できた。 An example in which ultra-low phosphorus steel could be manufactured was regarded as a passing example (example in which “◯” or “Δ” was indicated in the item “evaluation” in Table 2). In particular, among the examples that passed the test, examples where Si addition is unnecessary are indicated by “◯”. In Invention Examples 1 to 9, hot metal having a P content of less than 0.01% could be produced.
　但し、発明例８において、予備処理後の溶銑のＳｉ濃度及びＰ濃度が高かったため、発明例１～７に比較して、転炉処理後Ｐ濃度が高くなった。また、発明例９において、予備処理後の溶銑のＳｉ濃度は、転炉を用いた精錬工程において中間排滓をするには不十分であった。そのため、発明例９において、スラグを生成するために、転炉を用いた精錬工程においてＳｉが添加された。しかし、中間排滓をするに最低限のスラグ生成量であるため、発明例１～７に比較して、転炉処理後Ｐ濃度が高くなった。 However, in Invention Example 8, since the Si concentration and the P concentration of the hot metal after the preliminary treatment were high, the P concentration after the converter treatment was higher than those of Invention Examples 1 to 7. In Invention Example 9, the Si concentration in the hot metal after the preliminary treatment was insufficient for intermediate waste in the refining process using the converter. Therefore, in Invention Example 9, Si was added in a refining process using a converter to generate slag. However, since the amount of slag generated is minimum for intermediate waste, the P concentration after the converter treatment was higher than those of Invention Examples 1-7.
　比較例１～３は、Ｐ含有量が０．０１％未満の溶銑を製造できなかった例である（表２の項目「評価」において “×”が示された例）。比較例１～３において、予備処理後の溶銑のΔP／ΔSiは、０．１未満であった。 Comparative Examples 1 to 3 are examples in which hot metal having a P content of less than 0.01% could not be produced (example in which “x” was shown in the item “evaluation” in Table 2). In Comparative Examples 1 to 3, the ΔP / ΔSi of the hot metal after the pretreatment was less than 0.1.
　また、比較例１、３において、予備処理後の溶銑のＰ濃度は０．０９０質量％超であったが、予備処理後の溶銑のＳｉ濃度は、転炉を用いた精錬工程においてＰ濃度を低減するには不十分であった。そのため、比較例１、３において、溶銑中のＰを含有させるスラグを生成するために、転炉を用いた精錬工程においてＳｉが添加された。しかし、比較例１、３において、予備処理後の溶銑のＰ濃度が高過ぎたため、転炉による精錬処理によってＰ含有量が０．０１％未満の溶銑を製造できなかった。 Further, in Comparative Examples 1 and 3, the P concentration of the hot metal after the pretreatment was more than 0.090 mass%, but the Si concentration of the hot metal after the pretreatment was set to the P concentration in the refining process using a converter. Insufficient to reduce. Therefore, in Comparative Examples 1 and 3, Si was added in a refining process using a converter in order to generate slag containing P in the hot metal. However, in Comparative Examples 1 and 3, since the P concentration of the hot metal after the preliminary treatment was too high, hot metal having a P content of less than 0.01% could not be produced by refining treatment using a converter.
　比較例２において、予備処理後の溶銑のＳｉ濃度が十分に高かったので、転炉を用いた精錬工程においてＳｉを添加する必要はなかった。しかし、予備処理後の溶銑のＳｉ濃度及びＰ濃度が高かったため、転炉を用いた精錬工程におけるスラグ形成によるＰ濃度の低減処理が不十分になった。 In Comparative Example 2, since the Si concentration in the hot metal after the preliminary treatment was sufficiently high, it was not necessary to add Si in the refining process using a converter. However, since the Si concentration and the P concentration of the hot metal after the preliminary treatment were high, the P concentration reduction treatment due to slag formation in the refining process using the converter became insufficient.
　前述したように、本発明によれば、溶銑の予備処理において、ＣａＦ2を用いること無く、予備処理後の脱燐工程を妨げない程度に、溶銑中のＰ濃度及びＳｉ濃度を適度に低減しており、精錬工程で効率良く極低燐鋼を溶製できる。よって、本発明は、鉄鋼産業において利用可能性が高いものである。 As described above, according to the present invention, in the hot metal pretreatment, CaF 2 is not used, and the P concentration and Si concentration in the hot metal are appropriately reduced to such an extent that the dephosphorization step after the pretreatment is not hindered. Therefore, ultra-low phosphorus steel can be efficiently melted in the refining process. Therefore, the present invention has high applicability in the steel industry.
　１　　混銑車
　２　　開口部
　３　　ランス
　４　　溶銑
　５　　石灰系フラックス
　６　　酸化剤６
　６ａ　　酸化鉄
　７　　キャリアガス
　８　　スラグ
　９　　シュート 1 Chaos Wheel 2 Opening 3 Lance 4 Hot Metal 5 Lime-Based Flux 6 Oxidizing Agent 6
6a Iron oxide 7 Carrier gas 8 Slag 9 Chute

Claims (6)

  1. 　精錬容器内の溶銑に、酸化鉄、気体酸素、及び、石灰系フラックスを投入して、脱珪処理と脱燐処理を施す溶銑の予備処理方法において、
    　酸化鉄を酸化鉄換算の酸化剤原単位で２５ｋｇ／ｔ以上を投入するとともに、
    　上記投入の際、投入する酸化鉄の６０％以上を精錬容器の上方から投入して、
    　前記溶銑のＳｉ含有量を０．０５～０．３０質量％とし、且つＰ含有量を０．０４０～０．０８５質量％に調整することを特徴とする溶銑の予備処理方法。     In the hot metal pretreatment method in which iron oxide, gaseous oxygen, and lime-based flux are added to the hot metal in the refining vessel, and desiliconization treatment and dephosphorization treatment are performed.
    In addition to adding 25 kg / t or more of iron oxide in terms of iron oxide equivalent oxidant unit,
    At the time of the above charging, 60% or more of the iron oxide to be charged is charged from above the refining vessel,
    A hot metal preliminary treatment method, wherein the Si content of the hot metal is adjusted to 0.05 to 0.30 mass% and the P content is adjusted to 0.040 to 0.085 mass%.
  2. 　精錬容器内に投入される酸化鉄の全量のうち８０～１００％を精錬容器の上方から投入することを特徴とする請求項１に記載の溶銑の予備処理方法。 The hot metal pretreatment method according to claim 1, wherein 80 to 100% of the total amount of iron oxide charged into the smelting vessel is introduced from above the smelting vessel.
  3. 　予備処理前後のＰ濃度及び予備処理前後のＳｉ濃度が、下記式１を満たすことを特徴とする請求項１又は２に記載の溶銑の予備処理方法。
    　ΔＰ／ΔＳｉ＞０．１・・・（式１）
    　但し、ΔＰ：予備処理前Ｐ濃度と予備処理後Ｐ濃度との差、ΔＳｉ：予備処理前Ｓｉ濃度と予備処理後Ｓｉ濃度との差     The hot metal pretreatment method according to claim 1 or 2, wherein the P concentration before and after the pretreatment and the Si concentration before and after the pretreatment satisfy the following formula 1.
    ΔP / ΔSi> 0.1 (Expression 1)
    However, ΔP: difference between P concentration before pretreatment and P concentration after pretreatment, ΔSi: difference between Si concentration before pretreatment and Si concentration after pretreatment
  4. 　石灰系フラックスは、ＣａＦ2を含有しないことを特徴とする請求項１～３のうちいずれか１項に記載の溶銑の予備処理方法。 The hot metal pretreatment method according to any one of claims 1 to 3, wherein the lime-based flux does not contain CaF 2 .
  5. 　前記精錬容器が混銑車であることを特徴とする請求項１～４のうちいずれか１項に記載の溶銑の予備処理方法。 The hot metal pretreatment method according to any one of claims 1 to 4, wherein the smelting vessel is a chaotic vehicle.
  6. 　請求項１～５のうちいずれかに記載の予備処理方法後に、転炉での中間排滓を行うことを特徴とする極低燐鋼の製造方法。 6. A method for producing ultra-low phosphorus steel, characterized in that after the pretreatment method according to any one of claims 1 to 5, intermediate waste in a converter is performed.
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