WO2017122536A1 - 転炉吹錬方法 - Google Patents
転炉吹錬方法 Download PDFInfo
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- WO2017122536A1 WO2017122536A1 PCT/JP2016/088880 JP2016088880W WO2017122536A1 WO 2017122536 A1 WO2017122536 A1 WO 2017122536A1 JP 2016088880 W JP2016088880 W JP 2016088880W WO 2017122536 A1 WO2017122536 A1 WO 2017122536A1
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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
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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
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
- C21C5/30—Regulating or controlling the blowing
- C21C5/34—Blowing through the bath
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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
- C21C1/025—Agents used for dephosphorising or desulfurising
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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
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
-
- 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
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
- C21C5/36—Processes yielding slags of special composition
Definitions
- the present invention is a top-bottom converter, which removes phosphorus with a low Si concentration with a small amount of slag and performs a series of blowing from the hot metal without discharging the slag produced by the dephosphorization.
- the present invention relates to a converter blowing method for melting steel.
- Patent Document 1 discloses a method of using two converters, dephosphorizing the hot metal in one converter, and then decarburizing and blowing in the other converter. Yes.
- Patent Document 2 As a method for performing hot metal dephosphorization with a small amount of quicklime without using fluorite, a method of spraying a mixed powder of CaO powder, Al 2 O 3 powder, and Fe 2 O 3 powder together with oxygen gas onto hot metal is disclosed in Patent Document 2. Is disclosed. In this method, CaO powder, which is a main dephosphorizing agent, is sprayed onto a hot spot having a high temperature of 2000 ° C. or higher where the top blown oxygen and hot metal come into contact, and CaO having a high melting point is hatched relatively quickly. At this time, the hatching of CaO is further accelerated by mixing CaO and Al 2 O 3 that generates a low melting point compound.
- CaO powder which is a main dephosphorizing agent
- the slag produced by this method focuses only on the viewpoint of improving the dephosphorization efficiency at the hot metal stage, and as a series of blowing from the hot metal without discharging the slag produced by the dephosphorization, the decarburization blown It is unclear whether molten steel with a high C concentration and a low P concentration can be produced even if smelting is continued.
- Patent Document 3 discloses a method of producing molten steel having a low C concentration and a C concentration of 0.20 to 0.25% by mass by blowing up and blowing CaO powder together with top blowing oxygen gas in a converter. Is disclosed. However, in this method, since iron oxide is not blown up together with oxygen gas, the FeO concentration of the CaO—FeO-based melt in the slag generated at the fire point is low and the temperature of the fire point is high. Dephosphorization utilization efficiency as high as the method described in 1) cannot be obtained. Moreover, it is unclear whether the P concentration can be sufficiently reduced even when the C concentration is difficult to dephosphorize is 0.3 mass% or more.
- Patent Document 4 discloses a method for smelting high carbon molten steel in which lime powder is blown and sprayed for 70% or more of the blowing time.
- this method it is necessary to reduce the P concentration of the hot metal to 0.05% by mass or less in advance by a dephosphorization process that is separately performed, and the dephosphorization process and the decarburization process cannot be performed in a series of blowing processes. .
- the present invention has been made in view of the above-described problems, and an object thereof is to provide a converter blowing method for producing molten steel having a high C concentration and a low P concentration without interrupting blowing from the hot metal stage with a small amount of slag.
- the gist of the present invention is as follows. (1) A hot metal having a Si concentration of 0.15% by mass or less and a P concentration of 0.09% by mass or more is charged into the top-bottom blowing converter, and is a mixed powder of CaO powder and Fe 2 O 3 powder. A mixed powder in which the mass ratio of CaO and Fe 2 O 3 is 9: 1 to 6: 4 and the total of CaO, CaCO 3 , FeO, and Fe 2 O 3 is 95% by mass or more.
- molten steel having a high C concentration and a low P concentration can be produced with high efficiency without interrupting blowing from hot metal having a P concentration of 0.09 mass% or more with a small amount of slag.
- the molten steel having a high C concentration refers to a molten steel having a C concentration of 0.3 to 1.0% by mass
- the molten steel having a low P concentration refers to a molten steel having a P concentration of 0.02% by mass or less.
- molten iron having a Si concentration of 0.15% by mass or less (P concentration of 0.09% by mass or more) is charged into an upper bottom blowing converter, and CaO powder and Fe 2 are added.
- the CaO powder is mainly powdered lime, limestone or the like, and is mainly CaO or CaCO 3 .
- Fe 2 O 3 powder is mainly powdered iron ore and mainly composed of Fe 2 O 3 , but may contain FeO or crystal water.
- the CaO content is calculated by (CaO mass + CaCO 3 mass ⁇ 0.56).
- Fe 2 O 3 minutes is regarded as Fe 2 O 3 minutes including FeO.
- a mixed powder of CaO powder and Fe 2 O 3 powder is blown up onto the hot metal bath surface together with O 2 gas, and high basicity slag is generated at a fire point of 2000 ° C. or higher.
- a slag having a high basicity and a high FeO concentration is formed in the hot spot region, and reacts with P in the molten iron, so that a very high dephosphorization efficiency can be realized.
- the maximum particle size of the mixed powder is preferably set to 0.15 mm or less in consideration of the conveyance with O 2 gas and the ease of slag formation at the fire point.
- the activity of P in molten iron increases as the C concentration in molten iron increases. That is, the higher the C concentration in the molten iron, the easier the dephosphorization reaction proceeds. Therefore, when the relationship between the C concentration in the molten iron and the dephosphorization rate at the time of completion of blowing the mixed powder of CaO powder and Fe 2 O 3 powder was investigated, the C concentration in the molten iron was 2.5% by mass or more. the mixed powder of CaO powder and Fe 2 O 3 powder were blown upward together with O 2 gas while there, then, when the O 2 gas alone was blown on to the decarburization blowing, readily low high P concentration C concentration It has been found that molten steel can be produced.
- FeO in the slag is reduced by C in the molten iron, and as the FeO concentration in the slag decreases, a high melting point 2CaO.SiO 2 -3CaO.P 2 O 5 solid solution or 3CaO is contained in the molten slag.
- ⁇ P 2 O 5 solid phase crystallizes out.
- the remaining FeO in the liquid phase is further reduced, the melting point of the liquid phase slag rises, and the liquid phase slag solidifies.
- the mixed powder of CaO powder and Fe 2 O 3 powder is blown up to increase the dephosphorization rate, and then only O 2 gas is blown up.
- the temperature of the molten iron and slag continues to rise.
- high partial concentration of FeO is melted, is reduced by C in the molten iron.
- an object of the present invention is to provide a converter blowing method for producing molten steel having a high C concentration and a low P concentration without interrupting blowing from the hot metal stage with a small amount of slag.
- C concentration and P concentration at the end of blowing are unified to C: 0.85 to 0.99 mass%, P ⁇ 0.020 mass% (molten steel temperature is 1670 ⁇ 5 ° C.), and CaO powder
- the mixture concentration of CaO powder and Fe 2 O 3 powder is blown up oxygen, with the C concentration in the molten iron at the time of ending the mixed powder of Fe 2 O 3 powder being in the range of 2.5 to 3.6% by mass
- the steel was blown up while the C concentration in the molten iron together with the gas satisfied a predetermined concentration condition, and then only the O 2 gas was continuously blown up to produce molten steel.
- the Si concentration in the hot metal 0.05% by mass
- the mass ratio of CaO content and Fe 2 O 3 content in the mixed powder of CaO powder and Fe 2 O 3 powder is 4: 1, mixing
- the CaO content in the powder was unified at a rate of 10 to 15 kg / molten ton, 1.5 to 3.0 kg / min / molten ton, and an O 2 gas flow rate of 2.0 to 2.5 Nm 3 / min / molten ton.
- the C concentration in the molten iron at the time when the mixed powder is blown up is the relationship between the supply amount of the oxygen source (oxygen gas, iron oxide, etc.) and the amount of oxygen necessary for oxidizing the hot metal components (carbon, silicon) ( However, the oxygen utilization efficiency expected from operational experience is taken into account).
- Table 1 shows the blowing conditions and results.
- the ratio of the top-blown mixed powder shown in Table 1 indicates the ratio when impurities are removed, and in the mixed powder, the total of CaO content + Fe 2 O 3 minutes + Al 2 O 3 is 95% by mass or more. Shall.
- the top blowing speed of the CaO content in the mixed powder was set to 2.5 kg / min / molten ton, and decarburization blowing was performed at the same oxygen flow rate even after finishing the top blowing of the mixed powder.
- the Si concentration in the molten iron was 0.15% or less and the P concentration in the molten steel after the treatment could be set to a target value of 0.020% by mass or less.
- the top blowing speed of the CaO content in the mixed powder was 1.5 to 2.5 kg / min / molten ton, and decarburization blowing was performed at the same oxygen flow rate even after the top spraying of the mixed powder was completed.
- the flow rate of the top blown O 2 gas is 1.5 to 3.0 Nm 3 / min / molten ton, and the P concentration in the molten steel after treatment can be reduced to the target value of 0.020% by mass or less. I was able to confirm.
- the upper limit of the flow rate of O 2 gas is set to 3.0 Nm 3 / min / molten metal ton.
- the temperature of the CaO—FeO melt in the slag also becomes higher than when the Fe 2 O 3 powder is mixed and blown up.
- the dephosphorization reaction does not proceed easily, and the dephosphorization rate has become low even when the same CaO basic unit is blown up.
- the Fe 2 O 3 concentration in the mixed powder is as low as 5% by mass as in Comparative Example 3, it is considered that the P concentration in the molten steel after the treatment did not reach the target value.
- the CaO amount in the mixed powder is 10 to 15 kg / molten ton.
- the top blowing speed of the CaO content in the mixed powder is 1.5 to 3.0 kg / min / molten ton
- the P concentration in the molten steel after the treatment is set to a target value of 0.020% by mass or less. We were able to.
- the melting point of the CaO—FeO melt increased, the fluidity decreased, and the dephosphorization reaction rate decreased.
- the top blowing rate of the CaO content in the mixed powder is 1.5 to 3.0 kg / min / molten ton.
- Step 2 Next, based on what was confirmed in Step 1 above, hot metal having a Si concentration of 0.15 mass% or less and a P concentration of 0.09 mass% or more was charged into the top-bottom blown converter, and CaO A mixed powder of powder and Fe 2 O 3 powder and having a mass ratio of CaO and Fe 2 O 3 minutes of 9: 1 to 6: 4 is obtained at a flow rate of 1.5 to 3.0 Nm 3 / min.
- the C concentration in the molten steel at the point of time when the top blowing of the mixed powder is finished is 3.0 mass% or 3 Standardized to 1% by mass.
- the hot metal having a Si concentration lowered to 0.05% by mass by desiliconization treatment was charged into an upper bottom blowing converter, and Fe 2 O 3 was added to 96% by mass.
- the iron ore containing 6.3 kg / molten iron ton was added on top.
- the P concentration at the time after the end of the mixed powder top blowing is considered to be lower than the P concentration when the C concentration is 1.0% by mass.
- the experiment is based on the premise that a molten steel having a C concentration of 0.3 to 1.0% by mass is produced as a high C concentration, but this is particularly effective for molten steel having a C concentration of 0.8 to 1.0% by mass or more. Is more preferable because it becomes more prominent.
- 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.
- Example 2 The hot metal in which the Si concentration in the hot metal was reduced to 0.05% by mass by desiliconization was charged into the top-bottom blowing converter, and the iron ore containing 96% by mass of Fe 2 O 3 was increased to 6.3 kg / molten ton. Added.
- the flow rate of 2.5 Nm 3 / min / hot metal minute CaO with O 2 gas ton Fe 2 O 3 minutes and 4 in the weight ratio: 1 and the mixed powder (CaO in the powder mixture is 15 kg / hot metal ton) was blown off at the same oxygen flow rate even after finishing the top blowing of the mixed powder.
- the C concentration in the molten iron at the end of the top blowing of the mixed powder was 3.1% by mass.
- CO 2 gas was continuously blown from the tuyere installed at the bottom of the furnace at 0.1 Nm 3 / min / molten metal ton.
- the molten steel after the treatment was 1670 ° C., and in the molten steel, the C concentration was 0.98 mass%, the P concentration was 0.015 mass%, and the target P concentration was 0.020 mass% or less.
- the C concentration in the molten iron at the end of the top blowing of the mixed powder was 2.2% by mass.
- CO 2 gas was continuously blown from the tuyere installed at the bottom of the furnace at 0.1 Nm 3 / min / molten metal ton.
- the P concentration in the molten steel after the treatment was 0.023 mass%, and the target P concentration of 0.020 mass% or less could not be achieved.
- a high C concentration and a low P concentration molten steel can be produced with high efficiency without interrupting blowing from hot metal having a P concentration of 0.09 mass% or more with a small amount of slag. Industrial value is great.
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Abstract
Description
(1)上底吹き転炉へ、Si濃度が0.15質量%以下、かつ、P濃度が0.09質量%以上の溶銑を装入し、CaO粉及びFe2O3粉の混合粉であってCaO分とFe2O3分との質量比が9:1~6:4であり、かつCaO、CaCO3、FeO、及びFe2O3の合計が95質量%以上である混合粉を、流量1.5~3.0Nm3/min/溶銑tonの酸素ガスと共に上吹きし、上吹き中において、前記混合粉中のCaO分の上吹き量を10~15kg/溶銑tonとし、前記CaO分の供給速度を1.5~3.0kg/min/溶銑tonとして、溶鉄中のC濃度が2.5質量%以上である間に前記混合粉の上吹きを終了するようにし、前記混合粉の上吹きが終了した後も前記酸素ガスの上吹きを継続してC濃度が0.3質量%以上の溶鋼を製造することを特徴とする転炉吹錬方法。
(2)前記混合粉の最大粒径を0.15mm以下とすることを特徴とする(1)に記載の転炉吹錬方法。
(3)前記上吹き中において、さらにCO2ガスを0.05~0.3Nm3/min/溶銑ton底吹きすることを特徴とする(1)または(2)に記載の転炉吹錬方法。
まず、高炉から出銑されたP濃度が0.1質量%程度の溶銑に対して脱珪処理を施し、溶銑中のSi濃度を0.01~0.15質量%以下にした。その後、上底吹き転炉を用いて吹錬を行った。吹錬工程では、まず、脱珪処理された溶銑を上底吹き転炉へ装入し、その後、吹錬終了時の溶鋼温度を1670±5℃にすべく、温度調整剤としてFe2O3を96質量%含有する鉄鉱石を適宜添加した。次に、粒径が0.15mm以下のCaO粉のみもしくはCaO粉にFe2O3粉及びAl2O3粉のどちらかまたは両方をO2ガスに混合して上吹きした。
初めに、本発明の課題が「少ないスラグ量で、溶銑段階から吹錬を中断することなく、高いC濃度かつ低いP濃度の溶鋼を製造する転炉吹錬方法を提供すること」であることに鑑みて、吹錬終了時点でのC濃度とP濃度をC:0.85~0.99質量%でP≦0.020質量%(溶鋼温度は1670±5℃)に統一し、CaO粉及びFe2O3粉の混合粉を上吹きする終了時点の溶鉄中のC濃度を2.5~3.6質量%の範囲として、CaO粉及びFe2O3粉の混合粉を上吹き酸素ガスと共に溶鉄中のC濃度が所定の濃度の条件を満たしている間上吹きし、その後もO2ガスのみを上吹きし続けて、溶鋼を製造した。
このとき、「溶銑中Si濃度の影響、CaO粉及びFe2O3粉の混合粉の組成の影響、上吹き酸素ガスの流量の影響、上吹き中における混合粉中のCaO分の上吹き量の影響、前記CaO分の供給速度の影響」を確認した。
このとき、特に断らない限り、溶銑中Si濃度:0.05質量%、CaO粉及びFe2O3粉の混合粉中のCaO分とFe2O3分との質量比を4:1、混合粉中のCaO分は10~15kg/溶銑ton、1.5~3.0kg/min/溶銑tonの速度、O2ガス流量2.0~2.5Nm3/min/溶銑tonに統一した。また、混合粉を上吹きする終了時点の溶鉄中のC濃度は、酸素源(酸素ガス、酸化鉄、等)供給量と溶銑成分(炭素、シリコン)の酸化に必要な酸素量との関係(但し、操業経験から予想される酸素利用効率を考慮する)から計算によって求めた。
本発明例1~3では、Si濃度を脱珪処理により0.01~0.15質量%まで下げた溶銑を上底吹き転炉に装入し、Fe2O3を96質量%含有する鉄鉱石6.3kg/溶銑tonを上置き添加した。そして、流量が2.5Nm3/min/溶銑tonのO2ガスと共にCaO分とFe2O3分とを質量比で4:1とした混合粉(混合粉中のCaOは15kg/溶銑ton)を上吹きした。このとき、混合粉中のCaO分の上吹き速度を2.5kg/min/溶銑tonとして上吹きし、混合粉の上吹きを終了した後も同一酸素流量で脱炭吹錬した。その結果、溶銑中のSi濃度が0.15%以下で、処理後の溶鋼中のP濃度を目標値である0.020質量%以下にすることができると確認できた。
本発明例4~6では、Si濃度を脱珪処理により0.05質量%まで下げた溶銑を上底吹き転炉に装入し、Fe2O3を96質量%含有する鉄鉱石6.3~7.5kg/溶銑tonを上置き添加した。そして、流量が1.5~3.0Nm3/min/溶銑tonのO2ガスと共にCaO分とFe2O3分とを質量比で4:1とした混合粉(混合粉中のCaO分は10~15kg/溶銑ton)を上吹きした。このとき、混合粉中のCaO分の上吹き速度を1.5~2.5kg/min/溶銑tonとして上吹きし、混合粉の上吹きを終了した後も同一酸素流量で脱炭吹錬した。その結果、上吹きO2ガスの流量が1.5~3.0Nm3/min/溶銑tonで、処理後の溶鋼中のP濃度を目標値である0.020質量%以下にすることができると確認できた。
本発明例7~9及び比較例1~4では、Si濃度を脱珪処理により0.05質量%まで下げた溶銑を上底吹き転炉に装入し、Fe2O3を96質量%含有する鉄鉱石0~8.3kg/溶銑tonを上置き添加した。そして、流量が2.5Nm3/min/溶銑tonのO2ガスと共に、CaO粉のみ15kg/溶銑tonまたは20kg/溶銑ton、もしくは混合粉中のCaO分は15~20kg/溶銑tonとし、CaO分とFe2O3分との比率を変えた混合粉を、CaO粉または混合粉中のCaO分の上吹き速度を2.0~2.5kg/min/溶銑tonとして上吹きし、CaO粉または混合粉の上吹きを終了した後も同一酸素流量で脱炭吹錬した。その結果、混合粉におけるCaO分とFe2O3分との質量比が9:1~6:4である場合には、処理後の溶鋼中のP濃度を目標値である0.020質量%以下にすることができた。
比較例5では、CaO、Fe2O3及びAl2O3の混合粉を用い、表1に示す条件で吹錬を行ったところ、処理後の溶鋼中のP濃度は目標に達しなかった。この場合、スラグ中において火点で生成されるCaO-FeO-Al2O3融体は融点が低く、非常に流動性が高い。そのため、混合粉を上吹きしている間は非常に脱りん反応が効率良く進行する。しかしながら、その後の脱炭吹錬中に溶鉄の温度が上昇していくと、混合粉を上吹きしていた時に生成されたスラグが溶融し始めて、顕著に復りんしてしまったと考えられる。
本発明例10、11及び比較例6では、Si濃度を脱珪処理により0.05質量%まで下げた溶銑を上底吹き転炉に装入し、Fe2O3を96質量%含有する鉄鉱石6.3~8.0kg/溶銑tonを上置き添加した。そして、流量が2.5~3.5Nm3/min/溶銑tonのO2ガスと共にCaO分とFe2O3分とを質量比で4:1とした混合粉(混合粉中のCaOは8~15kg/溶銑ton)を、混合粉中のCaO分の上吹き速度を1.5~2.5kg/min/溶銑tonとして上吹きし、混合粉の上吹きを終了した後も同一酸素流量で脱炭吹錬した。その結果、混合粉中のCaO分が10~15kg/溶銑tonであれば、処理後の溶鋼中のP濃度を目標値である0.020質量%以下にすることができた。
本発明例12~14、比較例7~8では、Si濃度を脱珪処理により0.05質量%まで下げた溶銑を上底吹き転炉に装入し、Fe2O3を96質量%含有する鉄鉱石6.3~7.5kg/溶銑tonを上置き添加した。そして、流量が2.0~2.5Nm3/min/溶銑tonのO2ガスと共にCaO分とFe2O3分とを質量比で4:1とした混合粉(混合粉中のCaOは15kg/溶銑ton)を、混合粉中のCaO分の上吹き速度を1.3~3.5kg/min/溶銑tonとして上吹きし、混合粉の上吹きを終了した後も同一酸素流量で脱炭吹錬した。その結果、混合粉中のCaO分の上吹き速度が1.5~3.0kg/min/溶銑tonであれば、処理後の溶鋼中のP濃度を目標値である0.020質量%以下にすることができた。
次に、上記のStep1で確認したことを踏まえて、上底吹き転炉へ、Si濃度が0.15質量%以下、かつ、P濃度が0.09質量%以上の溶銑を装入し、CaO粉及びFe2O3粉の混合粉であってCaO分とFe2O3分との質量比が9:1~6:4である混合粉を、流量1.5~3.0Nm3/min/溶銑tonの酸素ガスと共に上吹きし、上吹き中において、前記混合粉中のCaO分の上吹き量を10~15kg/溶銑tonとし、前記CaO分の供給速度を1.5~3.0kg/min/溶銑tonとした条件下において、
溶鉄中のC濃度が所定濃度以上である間に前記混合粉の上吹きを終了するようにする効果と、前記混合粉の上吹きが終了した後も前記酸素ガスの上吹きを継続してC濃度が0.3質量%以上でP濃度が0.020%以下の溶鋼を製造することが安定して可能かどうかを確認した。なお、Step1の吹錬と同様に、処理後の溶鋼温度を調整するためにFe2O3を96質量%含有する鉄鉱石3.6~7.5kg/溶銑tonを上置き添加した。
この調査においては、上記した共通条件に加えて、処理後の溶鋼中のC濃度を0.80~1.00質量%に統一した。この調査の対象とした、本発明例4,6、12、13,17,18では、いずれも処理後のP濃度が0.020質量%以下を達成することができた。
この調査においては、上記した共通条件に加えて、混合粉の上吹きを終了する時点での溶鋼中のC濃度を3.0質量%または3.1質量%に統一した。この調査の対象とした、本発明例15~18では、Si濃度を脱珪処理により0.05質量%まで下げた溶銑を上底吹き転炉に装入し、Fe2O3を96質量%含有する鉄鉱石6.3kg/溶銑tonを上置き添加した。そして、流量が2.5Nm3/min/溶銑tonのO2ガスと共にCaO分とFe2O3分とを質量比で4:1とした混合粉(混合粉中のCaOは15kg/溶銑ton)を、混合粉中のCaO分の上吹き速度を2.5kg/min/溶銑tonとして上吹きし、混合粉上吹き終了後も同一酸素流量で脱炭吹錬した。その結果、処理後の溶鋼中のC濃度が0.3~1.0質量%の範囲で、処理後の溶鋼中のP濃度を目標値である0.020質量%以下にすることができることが分かった。
溶銑中のSi濃度を脱珪処理により0.05質量%まで下げた溶銑を上底吹き転炉に装入し、Fe2O3を96質量%含有する鉄鉱石6.3kg/溶銑tonを上置き添加した。そして、流量が2.5Nm3/min/溶銑tonのO2ガスと共にCaO分とFe2O3分とを質量比で4:1とした混合粉(混合粉中のCaOは15kg/溶銑ton)を、混合粉中のCaO分の上吹き速度を2.5kg/min/溶銑tonとして上吹きし、混合粉の上吹きを終了した後も同一酸素流量で脱炭吹錬した。混合粉の上吹き終了時点での溶鉄中のC濃度は3.1質量%だった。また、処理中は炉底に設置した羽口からCO2ガスを0.1Nm3/min/溶銑ton吹き込み続けた。
溶銑中のSi濃度を脱珪処理により0.05質量%まで下げた溶銑を上底吹き転炉に装入し、Fe2O3を96質量%含有する鉄鉱石8.3kg/溶銑tonを上置き添加した。そして、流量が2.5Nm3/min/溶銑tonのO2ガスと共にCaO分とFe2O3分とを質量比で4:1とした混合粉(混合粉中のCaOは20kg/溶銑ton)を、混合粉中CaO分の上吹き速度を1.5kg/min/溶銑tonとして上吹きし、混合粉上吹き終了後も同一酸素流量で脱炭吹錬した。混合粉の上吹き終了時点での溶鉄中のC濃度は2.2質量%だった。また、処理中は炉底に設置した羽口からCO2ガスを0.1Nm3/min/溶銑ton吹き込み続けた。
Claims (3)
- 上底吹き転炉へ、Si濃度が0.15質量%以下、かつ、P濃度が0.09質量%以上の溶銑を装入し、CaO粉及びFe2O3粉の混合粉であってCaO分とFe2O3分との質量比が9:1~6:4であり、かつCaO、CaCO3、FeO、及びFe2O3の合計が95質量%以上である混合粉を、流量1.5~3.0Nm3/min/溶銑tonの酸素ガスと共に上吹きし、上吹き中において、前記混合粉中のCaO分の上吹き量を10~15kg/溶銑tonとし、前記CaO分の供給速度を1.5~3.0kg/min/溶銑tonとして、溶鉄中のC濃度が2.5質量%以上である間に前記混合粉の上吹きを終了するようにし、前記混合粉の上吹きが終了した後も前記酸素ガスの上吹きを継続してC濃度が0.3質量%以上の溶鋼を製造することを特徴とする転炉吹錬方法。
- 前記混合粉の最大粒径を0.15mm以下とすることを特徴とする請求項1に記載の転炉吹錬方法。
- 前記上吹き中において、さらにCOガスまたはCO2ガスを0.05~0.3Nm3/min/溶銑ton底吹きすることを特徴とする請求項1または2に記載の転炉吹錬方法。
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