JP6379976B2 - Converter operation method - Google Patents
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Description
本発明は、溶銑を用いる転炉の操業方法に関する。 The present invention relates to a method for operating a converter using hot metal.
近年、低りん鋼への需要が高まっている一方で、環境への負荷を軽減する観点からスラグ排出量の削減も求められている。これらを両立するには、主な脱りん剤である生石灰の脱りん利用効率を向上することが重要となる。 In recent years, demand for low-phosphorus steel has increased, and reduction of slag emissions has also been demanded from the viewpoint of reducing environmental burden. In order to achieve both of these, it is important to improve the dephosphorization utilization efficiency of quicklime, which is the main dephosphorizing agent.
通常、転炉吹錬では、生石灰を吹錬前もしくは吹錬初期に全量添加する。すると、溶銑中におけるＳｉが酸化されることによって生成されるＳｉＯ2が生石灰の表層部にて高融点の２ＣａＯ・ＳｉＯ2層を形成し、生石灰の溶解速度を著しく低下させる。このような状態では、実質的なスラグ中の実塩基度（溶融しているスラグ中のＣａＯ／ＳｉＯ2質量比）が約２．０と低いので、スラグの脱りん能力が低い。転炉吹錬が進行して脱炭最盛期に達する頃には温度が上昇し、しかもスラグ中におけるＦｅＯ濃度が低下するため、このようにスラグの脱りん能力が低いと、復りんが生じて溶鋼中のＰ濃度が増加してしまい、中高炭低りん鋼を溶製することが困難であった。なお、以降の説明では、含有濃度に関する「％」は、特に断らない限り質量％の意味で用いるものとする。 Usually, in converter blowing, quick lime is added in its entirety before or at the beginning of blowing. Then, SiO 2 produced by oxidation of Si in the hot metal forms a high melting point 2CaO · SiO 2 layer in the surface layer portion of quicklime, and the dissolution rate of quicklime is significantly reduced. In such a state, since the actual basicity in the slag (CaO / SiO 2 mass ratio in the molten slag) is as low as about 2.0, the dephosphorization ability of the slag is low. The temperature rises when the converter blowing is advanced and the decarburization peak period is reached, and the FeO concentration in the slag decreases. The P concentration in the molten steel has increased, making it difficult to produce medium and high charcoal low phosphorus steel. In the following description, “%” related to the concentration is used in the meaning of mass% unless otherwise specified.
特許文献１には、Ｃ濃度が０．５％以上、Ｐ濃度が０．０１５％以下の中高炭低りん鋼を溶製するために、転炉吹錬中の酸素量が総量の４０〜７０％となっている間に、２回以上ＣａＯ源を装入する方法が開示されている。この方法では、吹錬中におけるスラグ中の実塩基度を低く、さらにスラグ中のＦｅＯ濃度を高く維持できる。そのため、吹錬途中で添加した生石灰の表層部に高融点の２ＣａＯ・ＳｉＯ2が形成されても、比較的短い時間で２ＣａＯ・ＳｉＯ2が高いＦｅＯ濃度の溶融スラグへ溶解するため、生石灰が溶解し易くなる。その結果、スラグの実塩基度が増加してスラグの脱りん能力が向上し、中高炭域（転炉吹錬終点時の溶鋼中のＣ濃度が０．５％以上）でもＰ濃度を０．０１５％以下にできるとしている。 In Patent Document 1, in order to melt medium-high coal low phosphorus steel having a C concentration of 0.5% or more and a P concentration of 0.015% or less, the amount of oxygen in the converter blowing is 40 to 70 of the total amount. %, A method of charging the CaO source twice or more is disclosed. In this method, the actual basicity in the slag during blowing is low, and the FeO concentration in the slag can be kept high. Therefore, even if 2CaO · SiO 2 with a high melting point is formed on the surface layer of quicklime added during the blowing, 2CaO · SiO 2 dissolves into molten slag with a high FeO concentration in a relatively short time, so that quicklime is dissolved. It becomes easy to do. As a result, the actual basicity of the slag is increased and the dephosphorization ability of the slag is improved, and the P concentration is reduced to 0. It can be reduced to 015% or less.
但し、特許文献１に記載の方法であっても、装入した生石灰は溶解しきれないため、スラグの実塩基度を高めるために生石灰添加量を増やし、装入塩基度を高めている。そのため、未溶解の生石灰量が増えてしまうという問題は残っている。ここで、装入塩基度とは「装入する副原料中のＣａＯ質量／｛（溶銑中のＳｉ質量＋スクラップ中のＳｉ質量）×２．１４＋装入する副原料中のＳｉＯ2質量｝で計算される値である。 However, even if it is the method of patent document 1, since the charged quicklime cannot melt | dissolve, in order to raise the real basicity of slag, the amount of quicklime additions is increased and the charged basicity is raised. Therefore, the problem that the amount of undissolved quicklime will increase remains. Here, the basicity of charging is “CaO mass in secondary raw material to be charged / {(Si mass in molten iron + Si mass in scrap) × 2.14 + SiO 2 mass in secondary raw material to be charged}”. The value to be calculated.
また、特許文献１に記載の方法では、ＣａＯ源の装入を、初装入を含めて３回以上に分け、その装入時毎に送酸速度を低下させる必要があるため、それによって滓化促進効果はあると考えられるが、その代わりに生産性低下を受容しなければならない。 Further, in the method described in Patent Document 1, it is necessary to divide the charging of the CaO source into three or more times including the initial charging, and to reduce the acid feed rate at each charging time. It is thought that there is an effect of promoting the conversion, but instead, a decrease in productivity must be accepted.
また、特許文献２には、平均粒径１ｍｍ以下の生石灰粉を吹錬末期まで上吹きして転炉吹錬する方法が開示されている。この方法では、融点が高く溶解し難い生石灰を平均粒径１ｍｍ以下として上吹き添加することにより溶解を促進し、その結果高い脱りん率が得られるとしている。 Further, Patent Document 2 discloses a method in which quick lime powder having an average particle diameter of 1 mm or less is blown up to the end of blowing and the converter is blown. In this method, quick lime, which has a high melting point and is difficult to dissolve, is added by top-blowing with an average particle diameter of 1 mm or less to promote dissolution, and as a result, a high dephosphorization rate is obtained.
特許文献１では、吹錬終了時における溶鋼中のＣ濃度が０．５％以上の場合は、未溶解生石灰がある程度残留するという問題があった。それに対し、吹錬終了時における溶鋼中のＣ濃度が０．５％以下の場合は、上吹き酸素による脱炭反応を進めてＣ濃度を下げるほどスラグ中のＦｅＯ濃度が上昇する。つまり、溶鋼中のＣ濃度が低下すると、上吹きした酸素が溶鋼と接触する領域（すなわち火点）に対してＣの供給速度が低下することによって、上吹き酸素と鉄とが反応して多量のＦｅＯを生成し始める。すると、未溶解の生石灰の表層部に生成していた２ＣａＯ・ＳｉＯ2が高ＦｅＯ濃度の溶融スラグ中へ徐々に溶解していく。 In patent document 1, when C density | concentration in the molten steel at the time of completion | finish of blowing is 0.5% or more, there existed a problem that undissolved quicklime remained to some extent. On the other hand, when the C concentration in the molten steel at the end of blowing is 0.5% or less, the FeO concentration in the slag increases as the decarburization reaction with the top blowing oxygen proceeds to lower the C concentration. That is, when the C concentration in the molten steel decreases, the supply rate of C decreases with respect to the region where the blown oxygen comes into contact with the molten steel (that is, the fire point). Begins to produce FeO. Then, 2CaO · SiO 2 generated in the surface layer of undissolved quicklime gradually dissolves into the molten slag having a high FeO concentration.
しかしながら、吹錬終了時における溶鋼中のＰ濃度を０．０１５％まで低減するために吹錬初期の装入塩基度を３．０以上にまで増加すると、吹錬終了時における溶鋼中のＣ濃度が０．０５％以上０．５％以下でスラグ中のＦｅＯ濃度が比較的高い場合であっても、未溶解の生石灰がスラグ中にある程度残留して、ＣａＯの脱りん効率が低くなってしまう。ここで、吹錬初期の装入塩基度とは、吹錬前および吹錬開始後の吹錬全期間の１０％が経過するまでの間に装入した副原料のみについて、「装入する副原料中のＣａＯ質量／｛（溶銑中のＳｉ質量＋スクラップ中のＳｉ質量）×２．１４＋装入する副原料のＳｉＯ2質量｝で計算される値である。 However, in order to reduce the P concentration in the molten steel at the end of blowing to 0.015%, if the charging basicity at the initial stage of blowing is increased to 3.0 or more, the C concentration in the molten steel at the end of blowing Is 0.05% or more and 0.5% or less, and even when the FeO concentration in the slag is relatively high, undissolved quicklime remains to some extent in the slag, and the dephosphorization efficiency of CaO becomes low. . Here, the charging basicity at the initial stage of blowing is defined as “subsidiary to be charged” only for the auxiliary raw materials charged before 10% of the entire blowing period before blowing and after the start of blowing. CaO mass in raw material / {(Si mass in hot metal + Si mass in scrap) × 2.14 + SiO 2 mass of auxiliary raw material to be charged}.
また、特許文献２に記載の方法では、平均粒径１ｍｍ以下の生石灰は溶解速度が速いので、生石灰の表層部に高融点の２ＣａＯ・ＳｉＯ2が形成され難く、スラグ全体の塩基度を速やかに高めて脱りんが促進されると考えられる。そのため、この方法は、比較的均一なスラグ全体を用いて脱りんを行う場合には有効と考えられる。但し、生石灰の粉体を供給するためには、吹錬によって発生するガスの気流によって飛散することを防止するための大掛かりな設備が必要であるという問題がある。そのため、このような微粒の粉体を供給せずに、同等以上の効果、すなわち生石灰溶解率が同レベルで、脱りん率が同等以上となる方法を開発することが必要である。 In addition, in the method described in Patent Document 2, quick lime having an average particle diameter of 1 mm or less has a high dissolution rate. Therefore, it is difficult to form a high melting point 2CaO · SiO 2 on the surface layer of quick lime, and the basicity of the entire slag is quickly increased. It is thought that dephosphorization is promoted. Therefore, this method is considered effective when dephosphorization is performed using a relatively uniform slag as a whole. However, in order to supply quicklime powder, there is a problem that a large facility is required to prevent scattering by the gas flow generated by blowing. For this reason, it is necessary to develop a method that does not supply such fine powder, but has the same or higher effect, that is, the quick lime dissolution rate is the same level and the dephosphorization rate is equal or higher.
本発明は前述の問題点に鑑みてなされたものであり、低コストであって、かつ脱りん率が高い転炉操業方法を提供することを目的としている。 The present invention has been made in view of the above-described problems, and an object thereof is to provide a converter operating method that is low in cost and has a high dephosphorization rate.
本発明者は、上記課題を解決するために鋭意検討を重ねた結果、質量％で、Ｓｉ濃度が０．２５〜０．６％の溶銑を転炉で吹錬し、吹錬終了時における溶鋼中のＣ濃度を０．０５％以上０．５％以下で、かつＰ濃度を０．０１５％以下にする際に、吹錬初期の装入塩基度を３．０〜４．５とし、そのための副原料としてのＣａＯ源及びＭｇＯ源に粒径３．３５〜９．５ｍｍのものを用いることにより、上記課題を解決できることを知見し、本発明を完成した。 As a result of intensive studies to solve the above-mentioned problems, the present inventor has blown hot metal having a mass concentration of 0.25 to 0.6% in a converter, and molten steel at the end of blowing. When the C concentration is 0.05% or more and 0.5% or less and the P concentration is 0.015% or less, the charging basicity at the initial stage of blowing is set to 3.0 to 4.5. It was found that the above problems could be solved by using a CaO source and an MgO source having a particle size of 3.35 to 9.5 mm as auxiliary materials of the present invention, and the present invention was completed.
ＣａＯ源としては、ＣａＯ含有率が９０質量％以上で気孔率が４０％以上の生石灰が最も好適であるが、ＣａＯを５０質量％以上含有する石灰石、消石灰、軽焼ドロマイト等を併用しても良い。ＭｇＯ源としては、ＭｇＯを３０質量％以上含有する軽焼ドロマイトが好適であるが、ＭｇＯを３０質量％以上含有するドロマイトや橄欖岩等も用いて良い。軽焼ドロマイトにはＣａＯが約６０質量％含まれるため、生石灰と併用するＣａＯ源としても好適である。 As the CaO source, quick lime having a CaO content of 90% by mass or more and a porosity of 40% or more is most suitable, but limestone, slaked lime, light-burned dolomite containing 50% by mass or more of CaO may be used in combination. good. As the MgO source, light-burned dolomite containing 30% by mass or more of MgO is suitable, but dolomite or peridotite containing 30% by mass or more of MgO may also be used. Since lightly burned dolomite contains about 60% by mass of CaO, it is also suitable as a CaO source used in combination with quicklime.
ここで、本発明における副原料としてのＣａＯ源及びＭｇＯ源の粒径は、最小で公称目開き３．３５ｍｍの篩いで篩ってその篩い上とし、最大でも公称目開き９．５ｍｍの篩いで篩ってその篩い下とする。なお、本発明では、基本的には副原料としてのＣａＯ源及びＭｇＯ源の粒径を３．３５〜９．５ｍｍとしているが、篩った後のＣａＯ源やＭｇＯ源の表面に付着した３．３５ｍｍ未満の粒径のものも一部含まれるものとする。 Here, the particle sizes of the CaO source and the MgO source as the auxiliary materials in the present invention are sieved with a sieve having a minimum nominal aperture of 3.35 mm, and are sieved with a sieve having a nominal aperture of 9.5 mm at the maximum. Sift to make it under the sieve. In the present invention, the particle sizes of the CaO source and the MgO source as the auxiliary materials are basically 3.35 to 9.5 mm. However, the particles 3 adhered to the surfaces of the CaO source and the MgO source after sieving. Some of the particles with a particle size of less than 35 mm are included.
粒径が最大でも９．５ｍｍの生石灰（一般的にＣａＯ含有率９０％以上で気孔率４０％以上）を用いると、Ｓｉ濃度が０．２５％以上の溶銑を吹錬する際に、吹錬初期の装入塩基度が３．０〜４．５で、吹錬終了時の溶鋼中のＣ濃度が０．０５％以上０．５％以下であれば、吹錬全期間の９０％が経過するまでに生石灰がほぼ溶解し、粒径が１０〜３０ｍｍの通常の塊生石灰を用いるよりも脱りん率が向上することが分かった。すなわち、上記条件下であれば、装入塩基度が同一であっても、粒径が通常の１０〜３０ｍｍの生石灰から最大でも粒径が９．５ｍｍの生石灰へ変更することによって、生石灰の溶解率を増加し、より高い脱りん率を実現できた。但し、添加する生石灰の粒径が小さくなると、通常の装入方法では酸素吹錬に伴って炉外へ飛散してしまう比率が高くなるため、粒径は３．３５ｍｍ以上にしておく必要がある。このように吹錬初期に装入する生石灰は粉体である必要はないということを、本発明者は見出した。 When quick lime with a particle size of 9.5 mm at the maximum (generally CaO content of 90% or more and porosity of 40% or more) is used to blow hot metal having a Si concentration of 0.25% or more. If the initial charging basicity is 3.0 to 4.5 and the C concentration in the molten steel at the end of blowing is 0.05% or more and 0.5% or less, 90% of the entire blowing period has elapsed. By this time, quick lime was almost dissolved, and it was found that the dephosphorization rate was improved as compared with using normal quick lime having a particle size of 10 to 30 mm. That is, under the above-mentioned conditions, even if the charging basicity is the same, the quick lime dissolution can be achieved by changing the normal particle size of quick lime having a particle size of 10 to 30 mm to quick lime having a particle size of 9.5 mm at the maximum. The rate was increased and higher dephosphorization rate was achieved. However, when the particle size of quicklime added is small, the ratio of scattering outside the furnace with oxygen blowing increases in the normal charging method, so the particle size must be 3.35 mm or more. . Thus, the present inventors have found that quick lime charged in the early stage of blowing does not have to be powder.
この粒径を小さくする効果は、通常の生石灰の気孔率が４０〜５０％と高いことを考えると、生石灰を用いる場合に最も大きく発揮されると考えられるが、ＣａＯを５０質量％以上含有する石灰石、消石灰、軽焼ドロマイト等であれば、ＣａＯ源としてこの効果を享受することができると考える。 The effect of reducing the particle size is considered to be most exhibited when using quicklime, considering that the porosity of normal quicklime is as high as 40 to 50%, but contains CaO in an amount of 50% by mass or more. If it is limestone, slaked lime, light-burned dolomite, etc., it is thought that this effect can be enjoyed as a CaO source.
溶銑中のＳｉ濃度は、吹錬によって溶融スラグを生成させるために０．２５％以上が必要である。このＳｉ濃度が０．２５％未満では、吹錬終了時の溶鋼中のＣ濃度が０．０５〜０．５％の条件ではスラグ生成量が少ない上に吹錬初期の装入塩基度が３．０〜４．５と高くないことから、吹錬終了時においてＰ濃度を０．０１５％以下にすることは困難である。一方、溶銑中のＳｉ濃度が０．６％を超える条件では、吹錬初期の装入塩基度を３．０〜４．５にまで高くしなくても、スラグ生成量が多いために吹錬終了時のＰ濃度を０．０１５％以下にすることは容易である。また、装入塩基度を下げるなら生石灰の溶融滓化も容易になるため、生石灰の粒径を小さくする効果も小さくなってしまう。以上のように、本発明において特に効果が顕著となる溶銑は、Ｓｉ濃度が０．２５〜０．６％のものである。 The Si concentration in the hot metal needs to be 0.25% or more in order to generate molten slag by blowing. When the Si concentration is less than 0.25%, the slag generation amount is small and the charging basicity at the initial stage of blowing is 3 when the C concentration in the molten steel at the end of blowing is 0.05 to 0.5%. Since it is not as high as 0.0 to 4.5, it is difficult to make the P concentration 0.015% or less at the end of blowing. On the other hand, under conditions where the Si concentration in the hot metal exceeds 0.6%, the slag generation amount is large even if the charging basicity at the initial stage of blowing is not increased to 3.0-4.5. It is easy to set the P concentration at the end to 0.015% or less. Further, if the charging basicity is lowered, it becomes easy to melt and hatch the quick lime, so that the effect of reducing the particle size of the quick lime becomes small. As described above, the hot metal that is particularly effective in the present invention has a Si concentration of 0.25 to 0.6%.
次に、上記方法に加えて、吹錬全期間の９０〜１００％が経過する間に生石灰を追加装入する場合は、その時点ではスラグの実塩基度（溶融スラグの分析塩基度）が３．０以上となっているため、追加装入した生石灰の表層部には高融点の２ＣａＯ・ＳｉＯ2が形成されない。そのため、通常用いている気孔率４０〜５０％の生石灰を吹錬全期間の９０〜１００％が経過している間に装入すると、生石灰の気孔中へＦｅＯ濃度の高い液相スラグが極めて速やかに侵入し、侵入したスラグ中のＦｅＯが極めて速やかにＣａＯ固相壁へ浸潤して生石灰を溶解してしまう。そして、その溶解した領域には、脱りん能の極めて高いＣａＯ−ＦｅＯ系スラグが生成し、その領域において局所的な高脱りん率（周囲の均一スラグ中のＰ濃度よりも、Ｐ濃度が顕著に高くなる状態）が実現されることを、本発明者は見出した。 Next, in addition to the above-mentioned method, when 90 to 100% of the entire blowing period has passed, when quick lime is additionally charged, the actual basicity of slag (analytical basicity of molten slag) is 3 at that time. Since it is 0.0 or more, high melting point 2CaO.SiO 2 is not formed on the surface layer of the quick lime that has been additionally charged. For this reason, when quick lime having a porosity of 40 to 50%, which is normally used, is charged while 90 to 100% of the entire blowing period has elapsed, a liquid phase slag with a high FeO concentration is rapidly introduced into the pores of the quick lime. The FeO in the infiltrated slag infiltrates the CaO solid phase wall very rapidly and dissolves quicklime. And in the melt | dissolved area | region, the CaO-FeO type | system | group slag with very high dephosphorization ability produces | generates, and the local high dephosphorization rate (P concentration is remarkable rather than P concentration in the surrounding uniform slag) in the area | region. The present inventor has found that a state in which the height is high) is realized.
但し、このような効果を実現するために、吹錬全期間の９０〜１００％が経過する間に生石灰を装入する場合には、生石灰の粒径を３．３５〜９．５ｍｍとする必要があると分かった。粒径が３．３５ｍｍ未満では、生石灰を装入後にスラグ中への溶解が早すぎて、比較的早期に均一スラグを形成してしまうため、上述した局所的な高脱りん率を実現できない。さらに、吹錬中に転炉内へ装入する影響により、装入した生石灰が転炉外へ飛散してしまう量が増えてしまう可能性もある。一方、粒径が９．５ｍｍ超では、生石灰の気孔中へスラグが侵入してＣａＯ固相壁へＦｅＯが浸潤する反応が間に合わず、未溶解部分が残留してしまう。 However, in order to realize such an effect, when quick lime is charged while 90 to 100% of the entire blowing period has elapsed, the particle size of quick lime needs to be 3.35 to 9.5 mm. I knew there was. When the particle size is less than 3.35 mm, the above-mentioned local high dephosphorization rate cannot be realized because the dissolution into the slag is too early after the quick lime is charged and the uniform slag is formed relatively early. Furthermore, due to the effect of charging into the converter during blowing, there is a possibility that the amount of quick lime charged will be scattered outside the converter. On the other hand, if the particle size is more than 9.5 mm, the reaction that slag enters the pores of quicklime and FeO infiltrates into the CaO solid phase wall is not in time, and the undissolved portion remains.
この吹錬全期間の９０〜１００％が経過する間に装入する生石灰は、生石灰が有する非常に高い気孔率という特性が重要であるため、他のＣａＯ源で代替することは難しい。 The quick lime charged during 90 to 100% of the entire blowing period is very difficult to replace with another CaO source because of the very high porosity characteristic of quick lime.
すなわち、本発明によれば、吹錬に使用するＣａＯ源及びＭｇＯ源に含まれるＣａＯを全部合計して算出される最終塩基度を従来と同程度としても、生石灰を中心とするＣａＯ源の粒径を従来の１０〜３０ｍｍから３．３５〜９．５ｍｍへと変更することにより、ＣａＯ源の溶解率を増加して、より高い脱りん率を実現することができる。 That is, according to the present invention, even if the final basicity calculated by adding up all the CaO contained in the CaO source and MgO source used for blowing is the same as the conventional one, the grains of the CaO source centered on quick lime. By changing the diameter from the conventional 10 to 30 mm to 3.35 to 9.5 mm, the dissolution rate of the CaO source can be increased and a higher dephosphorization rate can be realized.
なお、本発明は、溶銑脱りん実施後の溶銑を脱炭炉で吹錬する場合にも適用できる。但し、その場合、溶銑中のＳｉ濃度は極めて低いので、装入塩基度調整用に珪石等のＳｉＯ2源をＳｉＯ2の質量で溶銑１ｔ当たり４．９ｋｇ以上添加する。このようにＳｉＯ2源を装入することによって、転炉内でのスラグ生成条件を上記した非脱燐溶銑の転炉吹錬と同様にすることができる。このＳｉＯ2源も、ＳｉＯ2源自身の溶解速度を高め、もってＣａＯ源の溶融滓化を促進するために、粒径を３．３５〜９．５ｍｍとすることが適切である。この場合、ＣａＯ源及びＭｇＯ源と同様にＳｉＯ2源の粒径も、最小で公称目開き３．３５ｍｍの篩いで篩ってその篩い上とし、最大でも公称目開き９．５ｍｍの篩いで篩ってその篩い下とする。 In addition, this invention is applicable also when the hot metal after hot metal dephosphorization implementation is blown in a decarburization furnace. However, in this case, Si concentration in the hot metal so very low, adding molten iron 1t per 4.9kg or more of SiO 2 source such as silica stone mass of SiO 2 for charging basicity adjustment. By charging the SiO 2 source in this way, the slag generation conditions in the converter can be made the same as in the above-mentioned converter blowing of non-dephosphorized hot metal. The SiO 2 source also increase the dissolution rate of the SiO 2 source itself, have to promote the molten slag formation of CaO source, it is appropriate to 3.35~9.5mm particle size. In this case, similarly to the CaO source and the MgO source, the particle size of the SiO 2 source is also sieved with a sieve having a minimum nominal aperture of 3.35 mm, and sieved with a sieve having a nominal aperture of 9.5 mm at the maximum. I will make it under the sieve.
本発明によれば、転炉吹錬終点時点での温度、装入塩基度および転炉吹錬終点時の溶鋼中Ｃ濃度を同じとしても、装入する副原料としてのＣａＯ源及びＭｇＯ源、並びにＳｉＯ2源の粒径を適正な範囲に制御すれば、従来よりも脱りん率を向上させることができる。更には、吹錬全期間の９０〜１００％が経過している時に粒径と量とを適正にした生石灰を追加装入することにより、均一組成のスラグで脱りんする場合と比べ、生石灰の脱りん利用効率を向上して吹錬終了時における溶鋼中のＰ濃度を下げることができる。すなわち、生石灰を粉体として上吹きする方法と比べ、大掛かりな設備は不要であり、しかも同一のＣ濃度、Ｐ濃度の溶鋼を溶製するための生石灰の原単位を削減することができる。 According to the present invention, even when the temperature at the end of converter blowing, the basicity of charging, and the C concentration in molten steel at the end of converter blowing are the same, a CaO source and an MgO source as auxiliary materials to be charged, In addition, if the particle size of the SiO 2 source is controlled within an appropriate range, the dephosphorization rate can be improved as compared with the prior art. Furthermore, when 90 to 100% of the entire blowing period has elapsed, the addition of quick lime with an appropriate particle size and amount makes it faster than dephosphorization with a uniform composition of slag. The phosphorus removal utilization efficiency can be improved and the P concentration in the molten steel at the end of blowing can be lowered. That is, compared with the method in which quick lime is blown up as a powder, no large-scale equipment is required, and the basic unit of quick lime for melting molten steel having the same C concentration and P concentration can be reduced.
以下、本発明を実施するための形態を説明する。
まず、高炉から出銑された溶銑に対して、必要に応じて脱硫や脱珪処理を適宜実施して、Ｓｉ濃度が０．２５〜０．６％としたものを、適当なスクラップ量とともに通常の上底吹き機能を有する転炉に装入する。そして、所定の副原料を所定時期に装入することによってＣ濃度を０．５〜０．０５％とした溶鋼にする。
Hereinafter, modes for carrying out the present invention will be described.
First, the hot metal discharged from the blast furnace is appropriately subjected to desulfurization and desiliconization treatment as necessary so that the Si concentration is 0.25 to 0.6%, together with an appropriate amount of scrap. It is charged in the converter with the function of blowing the top and bottom. And it is set as the molten steel which made C density | concentration 0.5-0.05% by charging a predetermined | prescribed auxiliary material at a predetermined time.
この溶銑は、脱燐処理を施したものであってもよいが、脱燐処理を施すと溶銑中のＳｉ濃度は０．０２％以下になってしまうのが通常なので、そのような溶銑を対象とする場合には、上記溶銑中のＳｉ濃度に見合うＳｉＯ2源を、溶銑を転炉に装入する前、または装入後の吹錬初期（上吹き酸素の吹付けを開始してから上吹き酸素吹付けを終了する時点までの全吹錬時間の１０％が経過するまで）に転炉内に装入する。Ｓｉ濃度が０．２５〜０．６％に対応するＳｉＯ2装入量は、４．９〜１２．８ｋｇ／溶銑ｔである。 This hot metal may be subjected to a dephosphorization treatment. However, if the dephosphorization treatment is performed, the Si concentration in the hot metal is usually 0.02% or less. In this case, the SiO 2 source corresponding to the Si concentration in the hot metal is set to the initial stage of blowing (before starting the blowing of the top blown oxygen) before charging the hot metal into the converter or after charging. It is charged into the converter until 10% of the total blowing time up to the point when the blowing of oxygen is finished. The SiO 2 charge corresponding to the Si concentration of 0.25 to 0.6% is 4.9 to 12.8 kg / molten iron t.
このような溶銑を転炉に装入する前、吹錬開始前または吹錬開始後の吹錬初期に、粒径が３．３５〜９．５ｍｍのＣａＯ源、ＭｇＯ源を、初期装入塩基度が３．０〜４．５になるように調整して転炉内に装入する。ＭｇＯ源は、転炉の耐火物の溶損を抑制するために、吹錬後のスラグ中にＭｇＯが６〜１２％程度含まれるように装入する。ＭｇＯが６％未満では転炉耐火物の溶損が激しくなる。一方、ＭｇＯが１２％を超える条件では、スラグの流動性が低下してＣａＯ源の溶融滓化を阻害してしまう。 Before charging such hot metal into the converter, before the start of blowing, or at the initial stage of blowing after the start of blowing, the CaO source and MgO source having a particle size of 3.35 to 9.5 mm are used as the initial charging base. The temperature is adjusted to 3.0 to 4.5 and charged into the converter. The MgO source is charged so that about 6 to 12% of MgO is contained in the slag after blowing in order to suppress melting loss of the refractory in the converter. If MgO is less than 6%, the melting loss of the converter refractory becomes severe. On the other hand, under the condition that MgO exceeds 12%, the fluidity of the slag is lowered and the melting and hatching of the CaO source is inhibited.
このとき、吹錬終了時の温度を調整するために、酸化鉄を転炉内に装入しても良い。ここで、初期装入塩基度とは、吹錬前および吹錬開始後の吹錬全期間の１０％が経過するまでの間に装入した副原料のみについて、「装入する副原料中のＣａＯ質量／｛（溶銑中のＳｉ質量＋スクラップ中のＳｉ質量）×２．１４＋装入する副原料のＳｉＯ2質量｝で計算される値である。 At this time, iron oxide may be charged into the converter to adjust the temperature at the end of blowing. Here, the initial charge basicity refers to only the secondary raw material charged until 10% of the entire blowing period before blowing and after the start of blowing, CaO mass / {(Si mass in hot metal + Si mass in scrap) × 2.14 + SiO 2 mass of auxiliary raw material to be charged}.
この初期装入塩基度の調整は、目標となる吹錬終了時のＰ濃度に応じて行い、その目標となるＰ濃度が高い場合には初期装入塩基度を低めに設定し、目標となるＰ濃度が低い場合には初期装入塩基度を高めに設定する。このことは、操業の経験に基づいて適宜行えば良いことである。本発明の適用対象には、このＰ濃度の目標値が０．０１５％以下の低燐鋼を想定しているが、本発明の効果はこのＰ濃度の想定値に限られるものではない。 The initial charge basicity is adjusted according to the target P concentration at the end of blowing, and when the target P concentration is high, the initial charge basicity is set lower and becomes the target. When the P concentration is low, the basic charge basicity is set high. This can be done as appropriate based on operational experience. The target of application of the present invention is assumed to be low phosphorus steel having a target value of P concentration of 0.015% or less, but the effect of the present invention is not limited to the assumed value of P concentration.
酸化鉄は、スケール（ＦｅＯ、Ｆｅ2Ｏ3）、鉄鉱石、焼結鉱の一種以上、ＣａＯ源はＣａＯを５０％以上含有する生石灰、石灰石、消石灰、軽焼ドロマイトの一種以上、ＭｇＯ源はＭｇＯを３０％以上含有する軽焼ドロマイト、ドロマイト、橄欖岩、炭酸マグネシウムの一種以上、ＳｉＯ2源はＳｉＯ2を５０％以上含有する珪石、珪砂の一種以上とすることが適当である。 Iron oxide is one or more of scale (FeO, Fe 2 O 3 ), iron ore, and sintered ore, CaO source is one or more of quicklime, limestone, slaked lime, light-burned dolomite containing 50% or more of CaO, and MgO source is It is appropriate that at least one of lightly burned dolomite, dolomite, peridotite and magnesium carbonate containing 30% or more of MgO, and that the SiO 2 source be one or more of quartzite and silica sand containing 50% or more of SiO 2 .
上吹き酸素の吹付けを開始して上記所定の副原料を投入した後には、基本的には本発明の対象とする副原料は投入しない。但し、例外の一つとして、吹錬中にスラグが大きく泡立ちスロッピングが発生する懸念が認められたり、実際にスロッピングが発生してしまったりした場合には、ＣａＯ源やＭｇＯ源を鎮静剤として溶銑１ｔあたり３ｋｇ以下の量で転炉内へ投入することがある。しかし、この鎮静剤としての投入量はスロッピングによって転炉外へ排出されてしまうことがある上に、生石灰の反応効率を高められる条件を満たしていない時期で操業上止むを得ない投入であるために、本発明に係る副原料使用方法の技術的範囲には含めない。 After starting the blowing of top blowing oxygen and supplying the predetermined auxiliary material, basically, the auxiliary material which is the subject of the present invention is not input. However, as an exception, if there is a concern that slag is large and foaming slopping may occur during blowing, or if slopping actually occurs, use CaO source or MgO source as a sedative. In some cases, the amount is 3 kg or less per 1 ton of molten iron into the converter. However, the amount of the sedative used as a sedative may be discharged out of the converter due to slopping, and is unavoidable in terms of operation when the conditions for improving the reaction efficiency of quicklime are not satisfied. Therefore, it is not included in the technical scope of the method for using auxiliary materials according to the present invention.
以上のようにして吹錬を行い、溶銑中のＣ濃度が０．５〜０．０５％の範囲内の目標値に到達した時点で上吹き酸素の吹付けを止めて、吹錬を終了する。このＣ濃度の目標値に到達した時点の判断は、通常の吹錬制御方法により行うものとする。 Blowing is performed as described above, and when the C concentration in the molten iron reaches the target value within the range of 0.5 to 0.05%, the blowing of the top blowing oxygen is stopped and the blowing is finished. . The judgment at the time when the target value of the C concentration is reached is made by a normal blowing control method.
もう一つの例外としては、その通常の吹錬制御方法により得られる酸素吹付け予定時間がその９０％を経過した時点以降の酸素吹付け中に、粒径が３．３５〜９．５ｍｍの生石灰を、最終装入塩基度が前記初期装入塩基度よりも０．１〜０．５の範囲で高くなる量だけ追加投入する方法がある。この追加投入は、後述するように生石灰の反応効率を低下させずに溶鋼中のＰ濃度を低下させることができるので、吹錬終了時のＰ濃度を一層低下させるためには前記の基本的な実施態様よりも好ましい実施態様と言える。 Another exception is quick lime with a particle size of 3.35 to 9.5 mm during the oxygen spray after the 90% of the scheduled oxygen spray time obtained by the normal blowing control method has passed. Is added in an amount such that the final charge basicity is higher in the range of 0.1 to 0.5 than the initial charge basicity. As will be described later, this additional charging can reduce the P concentration in the molten steel without reducing the reaction efficiency of quicklime, so that the basic concentration described above is required to further reduce the P concentration at the end of blowing. It can be said that it is a preferable embodiment rather than an embodiment.
以上における本発明に係る数値範囲は、次のようにして確かめた。
まず、Ｓｉ濃度が約０．３％（一部のみ約０．５％）、Ｐ濃度が約０．１０％である溶銑約２７０ｔを２０〜３０ｔのスクラップとともに転炉へ装入した。そして、粒径１０〜３０ｍｍもしくは３．３５〜９．５ｍｍの生石灰（ＣａＯ約９５％）および軽焼ドロマイト（ＣａＯ約６０％、ＭｇＯ約３４％）を添加して初期装入塩基度を２．８〜５．０、転炉スラグ中のＭｇＯ濃度を６〜１２％とする条件で吹錬を行った。このときの吹錬の条件は、上吹き酸素流量６００００Ｎｍ3／ｈ、底吹きＣＯ2流量２０００Ｎｍ3／ｈであった。また、吹錬の途中に粒径範囲が１〜３ｍｍ、３．３５〜９．５ｍｍ、１０〜３０ｍｍのいずれかの細粒生石灰を、装入塩基度が初期装入塩基度から最大０．６増加する分だけ装入した。
The numerical range according to the present invention described above was confirmed as follows.
First, about 270 t of hot metal having a Si concentration of about 0.3% (partially about 0.5%) and a P concentration of about 0.10% was charged into the converter together with 20-30 t of scrap. Then, quick lime (CaO about 95%) and light calcined dolomite (CaO about 60%, MgO about 34%) having a particle size of 10 to 30 mm or 3.35 to 9.5 mm are added to adjust the initial charge basicity to 2. Blowing was performed under the conditions of 8 to 5.0 and the MgO concentration in the converter slag being 6 to 12%. The blowing conditions at this time were an upper blowing oxygen flow rate of 60000 Nm 3 / h and a bottom blowing CO 2 flow rate of 2000 Nm 3 / h. Also, during the smelting process, any fine-grained quicklime having a particle size range of 1 to 3 mm, 3.35 to 9.5 mm, or 10 to 30 mm is used. It was charged as much as it increased.
この調査では、初期装入塩基度の計算対象時期（吹錬開始前および吹錬開始から吹錬全期間の１０％が経過する時まで）、及び生石灰の追加投入対象時期（吹錬開始から吹錬全期間の９０％が経過した時点以降吹錬終了時まで）以外には、ＣａＯ含有副原料やＳｉＯ2源は転炉内に一切投入しなかった。 In this survey, the initial charging basicity calculation period (before the start of blowing and until 10% of the total period of blowing has elapsed since the start of blowing) and the timing of additional charging of quick lime (from the start of blowing) Except for 90% of the entire smelting period until the end of blowing, no CaO-containing auxiliary material or SiO 2 source was charged into the converter.
結果を表１（発明例）及び表２（比較例）に示すが、各条件で５Ｃｈ行った平均値を載せている。吹錬終了時の溶鋼中の溶鋼温度は１６４０〜１６６０℃であった。評価基準は、最終装入塩基度、及び吹錬終了時における溶鋼中のＣ濃度を同等として比較したときに、従来法、すなわち１０〜３０ｍｍの生石灰を吹錬初期に添加した場合の吹錬終了時における溶鋼中のＰ濃度よりも低下していれば「○」とし、その中で３．３５〜９．５ｍｍの生石灰を吹錬初期（吹錬開始から吹錬全期間の１０％が経過する時まで）に添加した場合よりもＰ濃度が低下した場合に「◎」とした。 Although a result is shown in Table 1 (invention example) and Table 2 (comparative example), the average value performed 5Ch on each condition is carried. The molten steel temperature in the molten steel at the end of blowing was 1640 to 1660 ° C. The evaluation criteria are that when the final charge basicity and the C concentration in the molten steel at the end of blowing are compared, the conventional method, that is, the end of blowing when 10-30 mm quicklime is added at the initial stage of blowing. If it is lower than the P concentration in the molten steel at that time, it will be “◯”, and in that time 3.35-9.5 mm quicklime will be blown early (10% of the entire period of blowing will elapse since the start of blowing) “◎” when the P concentration was lower than when it was added by the time).
（１）生石灰の追加装入による効果
サンプルＮｏ．１０１は、従来の方法として、吹錬開始前及び開始直後に粒径１０〜３０ｍｍの塊生石灰を全て装入した場合であり、吹錬終了時における溶鋼中のＰ濃度は０．０１９％であった。これに対し、サンプルＮｏ．１は、粒径３．３５〜９．５ｍｍの細粒生石灰を全て吹錬開始前に装入した場合であり、サンプルＮｏ．２は、吹錬開始前から吹錬全期間の１０％までの間に粒径３．３５〜９．５ｍｍの細粒生石灰を全て装入した場合である。これらのサンプルは、吹錬終了時において溶鋼中のＰ濃度は０．０１５％まで低下した。
(1) Effect of additional charging of quicklime Sample No. 101 is a case where, as a conventional method, all lump lime having a particle diameter of 10 to 30 mm is charged before and immediately after the start of blowing, and the P concentration in the molten steel at the end of blowing is 0.019%. It was. In contrast, sample no. No. 1 is a case where all the fine quicklime having a particle size of 3.35 to 9.5 mm is charged before the start of blowing. 2 is the case where all the fine quicklime having a particle size of 3.35 to 9.5 mm was charged between before the start of blowing and up to 10% of the entire period of blowing. In these samples, the P concentration in the molten steel decreased to 0.015% at the end of blowing.
サンプルＮｏ．１０１の場合は、添加した生石灰の表層部に高融点の２ＣａＯ・ＳｉＯ2が生成して、生石灰の溶解速度が低下して、生石灰の脱りん利用効率が低くなってしまったと考えられる。これに対してサンプルＮｏ．１及び２では、初期に装入した細粒生石灰の表層部に高融点の２ＣａＯ・ＳｉＯ2は生成するものの、その内側に残された未溶解ＣａＯの量がかなり減っていたため、吹錬終了時までに十分溶解できたことにより脱りん速度が向上し、吹錬終了時における溶鋼中のＰ濃度が従来よりも低下したと考えられる。 Sample No. In the case of 101, it is considered that 2CaO.SiO 2 having a high melting point was formed in the surface layer portion of the added quicklime, the dissolution rate of quicklime was reduced, and the dephosphorization utilization efficiency of quicklime was lowered. In contrast, sample no. In 1 and 2, although high melting point 2CaO · SiO 2 was generated in the surface layer of fine-grained quicklime initially charged, the amount of undissolved CaO remaining on the inside was considerably reduced. It is considered that the dephosphorization rate was improved by being sufficiently dissolved by the time, and the P concentration in the molten steel at the end of blowing was lower than before.
更には、サンプルＮｏ．３及び４は、吹錬全期間の９０〜１００％が経過している間に細粒生石灰を装入した場合であり、吹錬終了時における溶鋼中のＰ濃度がそれぞれ０．０１５％、０．０１４％となり、サンプルＮｏ．１０１よりも低いＰ濃度であった。特に、サンプルＮｏ．４は、サンプルＮｏ．１及び２よりもＰ濃度が低くなった。細粒生石灰を追加装入する時は、スラグ中のＦｅＯ濃度が高く、温度も高かったため、装入した細粒生石灰が速やかに溶解して脱りんに寄与したため、吹錬終了時における溶鋼中のＰ濃度が更に低下したと考えられる。 Furthermore, sample no. 3 and 4 are cases where fine quicklime is charged while 90 to 100% of the entire blowing period has elapsed, and the P concentration in the molten steel at the end of blowing is 0.015% and 0, respectively. 014%, sample no. The P concentration was lower than 101. In particular, sample no. 4 is Sample No. P concentration was lower than 1 and 2. When the fine quicklime was additionally charged, the FeO concentration in the slag was high and the temperature was high, so the charged fine quicklime was quickly dissolved and contributed to dephosphorization. It is considered that the P concentration further decreased.
前述したように、吹錬中期までは溶融スラグの実塩基度は約２．０程度なため、このときにそのスラグへ生石灰が添加されると、生石灰の表層部に高融点の２ＣａＯ・ＳｉＯ2層が形成されてしまい、生石灰の溶解が阻害される。ところが、吹錬末期ではスラグ中の実塩基度が３．０ぐらいに上昇し、ＦｅＯ濃度も高くなると、そのスラグへ生石灰が添加されたた場合は、生石灰の表層部に２ＣａＯ・ＳｉＯ2層が形成されず、生石灰の気孔中（通常の生石灰の気孔率は４０％以上と高い）へ高いＦｅＯ濃度のスラグが急速に侵入し、さらにＣａＯ固相壁へＦｅＯが速やかに浸潤して、細粒生石灰は速やかに溶解する。そして、生石灰中のＣａＯはＦｅＯと低融点の化合物、すなわちカルシウムフェライトを生成し易く、そのカルシウムフェライトの脱りん能力は極めて高い。本発明では、このカルシウムフェライトに近い組成のスラグを局所的に且つ速やかに生成させることにより、均一組成のスラグで脱りんする場合よりも、脱りんを促進できたと考えられる。これが、本発明における重要な機構である。 As described above, since the actual basicity of the molten slag is about 2.0 until the middle stage of blowing, when quick lime is added to the slag at this time, the high melting point 2CaO.SiO 2 is added to the surface layer of the quick lime. A layer is formed, and dissolution of quicklime is inhibited. However, when the actual basicity in the slag rises to about 3.0 and the FeO concentration increases at the end of blowing, when quick lime is added to the slag, the 2CaO.SiO 2 layer is formed on the surface of the quick lime. Slag with a high FeO concentration rapidly penetrates into the pores of quicklime (the porosity of ordinary quicklime is as high as 40% or more), and FeO rapidly infiltrates into the CaO solid phase wall. Quicklime dissolves quickly. And CaO in quicklime tends to produce | generate the compound of FeO and a low melting point, ie, calcium ferrite, and the dephosphorization ability of the calcium ferrite is very high. In the present invention, it is considered that dephosphorization could be promoted by generating slag having a composition close to that of calcium ferrite locally and promptly as compared with the case of dephosphorization with slag having a uniform composition. This is an important mechanism in the present invention.
一方、サンプルＮｏ．３のように吹錬全期間の９０〜１００％が経過した時に装入する生石灰が多過ぎても、生石灰がスラグ中の限られた量のＦｅＯを奪い合う形になってしまい、結果として生石灰がＦｅＯと反応して溶解しきれず、Ｐ濃度低下の効果が十分に発揮されなかったものと考えられる。 On the other hand, sample no. Even if too much quick lime is charged when 90 to 100% of the entire blowing period has passed as in 3, the quick lime competes with a limited amount of FeO in the slag, resulting in quick lime It is considered that the reaction with FeO did not completely dissolve, and the effect of lowering the P concentration was not fully exhibited.
（２）溶銑中のＳｉ濃度の影響
サンプルＮｏ．５は、溶銑中のＳｉ濃度が０．５％であり、他のサンプルよりも高い。この場合は、サンプルＮｏ．４と装入塩基度が同じであるが、スラグ量が多いため、吹錬終了時における溶鋼中のＰ濃度は、サンプルＮｏ．４より低下した。
(2) Influence of Si concentration in hot metal Sample No. In No. 5, the Si concentration in the hot metal is 0.5%, which is higher than other samples. In this case, sample no. 4 and the charging basicity is the same, but since the amount of slag is large, the P concentration in the molten steel at the end of blowing is determined as Sample No. It was lower than 4.
（３）初期装入塩基度の差
サンプルＮｏ．１０２は、初期装入塩基度を２．８として、吹錬全期間の９０〜１００％が経過している間に細粒生石灰を添加して最終装入塩基度を３．３とした場合である。この場合は、初期装入塩基度を３．０としたサンプルＮｏ．４よりも吹錬終了時における溶鋼中のＰ濃度は高くなってしまった。サンプルＮｏ．１０２では、初期装入塩基度が低かったため、吹錬中期までスラグの脱りん能力が低く、吹錬全期間の９０〜１００％が経過して細粒生石灰を添加する段階で溶鋼中のＰ濃度が高く、細粒生石灰を添加しても脱りん能力を十分な値まで向上させることができなかったと考えられる。
(3) Difference in initial charge basicity Sample No. 102, when the initial charge basicity was set to 2.8 and fine granulated lime was added while 90 to 100% of the entire blowing period had elapsed, and the final charge basicity was set to 3.3. is there. In this case, sample no. The P concentration in the molten steel at the end of blowing was higher than 4. Sample No. In No. 102, since the initial charge basicity was low, the dephosphorization ability of slag was low until the middle stage of blowing, and the P concentration in the molten steel was added at the stage where 90 to 100% of the total duration of blowing was added and fine quicklime was added. It is considered that the dephosphorization ability could not be improved to a sufficient value even when fine lime was added.
また、サンプルＮｏ．１０３は、初期装入塩基度が５．０の場合であり、この場合には、吹錬全期間の９０〜１００％が経過している間に細粒生石灰を添加しても、吹錬終了点における溶鋼中のＰ濃度は０．０１６％となった。初期装入塩基度が高過ぎると、吹錬中期のスラグ中のＦｅＯ濃度が低くなってしまうことから脱りん速度が低下し、溶鋼中のＰ濃度が高い値で推移するため、吹錬末期に添加した細粒生石灰がスラグ中のＦｅＯと十分に反応しきれず、脱りんが進行し難かったためと考えられる。 Sample No. 103 is a case where the initial charging basicity is 5.0, and in this case, even if 90 to 100% of the entire blowing period has elapsed, the addition of fine lime is completed. The P concentration in the molten steel at the point was 0.016%. If the initial charge basicity is too high, the FeO concentration in the slag in the middle of the blowing process will be low, so the dephosphorization rate will decrease, and the P concentration in the molten steel will remain at a high value. This is probably because the added fine-grained quicklime could not sufficiently react with FeO in the slag and dephosphorization did not proceed easily.
（４）生石灰を追加装入する際の装入時期
最終装入塩基度が同一であるサンプル同士を比較すると、吹錬開始前または開始直後における装入塩基度を３．０〜４．２とした場合に、細粒生石灰を吹錬全期間の０〜１０％が経過する迄に追加装入したサンプルＮｏ．２、６、８、１０よりも、吹錬全期間の９０〜１００％が経過する間に追加装入したサンプルＮｏ．４、７、９、１１の方が、吹錬終了時における溶鋼中のＰ濃度を低くすることができた。すなわち、最終装入塩基度が同一とする場合、吹錬初期に追加装入するよりも吹錬全期間の９０〜１００％が経過する間に細粒生石灰を追加装入する方が、ＣａＯの脱りん利用効率が高く吹錬終了時における溶鋼中のＰ濃度を低下させられることが分かった。
(4) Charging time when additional quicklime is charged When comparing samples having the same final charging basicity, the charging basicity before or immediately after the start of blowing is 3.0 to 4.2. In this case, sample No. 1 in which fine quicklime was additionally charged until 0 to 10% of the entire blowing period had elapsed. Sample No. 2 additionally charged while 90 to 100% of the entire blowing period passed than 2, 6, 8, and 10. 4, 7, 9, and 11 were able to lower the P concentration in the molten steel at the end of blowing. That is, when the final charge basicity is the same, it is better to add the fine quicklime during 90 to 100% of the entire blowing period than to add the charge early in the blowing process. It was found that the phosphorus removal efficiency is high and the P concentration in the molten steel at the end of blowing is reduced.
（５）生石灰の粒径の差
サンプルＮｏ．１０４は、吹錬全期間の９０〜１００％が経過している間に装入する細粒生石灰の粒径を１〜３ｍｍとした場合であり、細粒生石灰の粒径を３．３５〜９．５ｍｍとしたサンプルＮｏ．１及びＮｏ．４に比べ、吹錬終了時における溶鋼中のＰ濃度が高く、０．０１６％となった。このように粒径が１〜３ｍｍである細粒生石灰を転炉へ装入すると、飛散ロスが多くなり過ぎたため、装入量の割に脱りんに寄与しなかったと考えられる。また、粒径が３ｍｍ未満では、装入後のスラグ中への溶解が早すぎて、比較的早期に均一スラグを形成してしまうため、上述した局所的な高脱りん率を実現できなかったことも原因と考えられる。
したがって、サンプルＮｏ．１０４においても、初期装入塩基度を粒径３．３５〜９．５ｍｍの細粒生石灰を用いて調整する効果は奏されていると考えられるものの、追加装入する生石灰の粒径が所定の３．３５〜９．５ｍｍから外れている場合には、その追加生石灰中ＣａＯの脱りん利用効率が初期装入された生石灰のそれよりも劣っているため、吹錬全体としてのＣａＯの脱りん利用効率を高められないことが分かった。
(5) Difference in quick lime particle size Sample No. 104 is a case where the particle size of the fine lime is 1 to 3 mm while 90 to 100% of the entire blowing period has elapsed, and the particle size of the fine lime is 3.35 to 9 Sample No. 5 mm. 1 and no. Compared to 4, the P concentration in the molten steel at the end of blowing was high, which was 0.016%. In this way, when fine quicklime having a particle diameter of 1 to 3 mm was charged into the converter, the scattering loss increased, and it was considered that it did not contribute to dephosphorization for the charged amount. In addition, when the particle size is less than 3 mm, the dissolution in the slag after charging is too early, and a uniform slag is formed relatively early, so the above-described local high dephosphorization rate could not be realized. This is also considered to be the cause.
Therefore, sample no. In 104, although it is considered that the effect of adjusting the initial charging basicity using fine-grained quick lime having a particle size of 3.35 to 9.5 mm is achieved, the particle size of the quick lime to be additionally charged is predetermined. When it deviates from 3.35 to 9.5 mm, the dephosphorization utilization efficiency of CaO in the additional quicklime is inferior to that of the initially charged quicklime. It turned out that utilization efficiency cannot be improved.
一方、サンプルＮｏ．１０５は、吹錬末期に添加した生石灰の粒径を１０〜２０ｍｍとした場合であり、細粒生石灰の粒径を３．３５〜９．５ｍｍとしたサンプルＮｏ．１及び４に比べ、吹錬終了時における溶鋼中のＰ濃度が高く、０．０１６％となった。この場合は、生石灰の気孔中へスラグが侵入し、ＣａＯ固相壁へＦｅＯが浸潤するのが間に合わず、未溶解部分が残留してしまったために、脱りんに十分寄与できず、吹錬終了時における溶鋼中のＰ濃度がサンプルＮｏ．１よりも高くなってしまったと考えられる。したがって、サンプルＮｏ．１０５においても、サンプルＮｏ．１０４で確認したことと同様なことが確認されたと言える。 On the other hand, sample no. No. 105 is a case where the particle size of quicklime added at the end of blowing is set to 10 to 20 mm. Sample No. 105 in which the particle size of fine-grained quicklime is 3.35 to 9.5 mm. Compared with 1 and 4, the P concentration in the molten steel at the end of blowing was high, which was 0.016%. In this case, slag penetrates into the pores of quicklime, and it is not in time for FeO to infiltrate the CaO solid phase wall, and the undissolved part remains, so it cannot contribute sufficiently to dephosphorization, and the blowing is completed. The P concentration in the molten steel at the time of the sample No. It is thought that it became higher than 1. Therefore, sample no. Also in sample 105, sample no. It can be said that the same thing as what was confirmed in 104 was confirmed.
（６）装入塩基度の上昇幅の差
サンプルＮｏ．４、１３及び１４は、それぞれ吹錬全期間の９０〜１００％が経過している間に装入塩基度が０．１〜０．５上昇するように細粒生石灰を装入した場合である。また、サンプルＮｏ．１２は、吹錬全期間の９０〜１００％が経過している間に装入塩基度が０．０５上昇するように細粒生石灰を装入した場合である。これらのサンプルを比較すると、サンプルＮｏ．１２は、サンプルＮｏ．４、１３及び１４よりも吹錬終了時における溶鋼中のＰ濃度は高かった。吹錬全期間の９０〜１００％が経過している間における細粒生石灰の装入量が少な過ぎると、上述したようにカルシウムフェライトに近い組成のスラグを局所的に且つ速やかに生成させて、均一組成のスラグで脱りんさせることができず、脱りんを促進する効果を享受できなかったためと考えられる。但し、吹錬初期に装入した生石灰は３．３５〜９．５ｍｍの細粒であるため、サンプルＮｏ．１０１よりは脱りん率が向上し、吹錬終了時における溶鋼中のＰ濃度が０．０１５％以下である低りん鋼を溶製することはできた。
(6) Difference in increase in charge basicity Sample No. 4, 13 and 14 are cases in which fine quicklime is charged so that the charging basicity rises by 0.1 to 0.5 while 90 to 100% of the entire blowing period has elapsed. . Sample No. 12 is the case where fine-grained quicklime is charged so that the charging basicity increases by 0.05 while 90 to 100% of the entire blowing period has elapsed. When these samples are compared, sample no. 12 is Sample No. The P concentration in the molten steel at the end of blowing was higher than 4, 13, and 14. When 90 to 100% of the entire blowing period has elapsed, the amount of fine-grain quicklime is too small, and as described above, a slag having a composition close to calcium ferrite is generated locally and quickly, This is probably because the slag having a uniform composition could not be dephosphorized and the effect of promoting dephosphorization could not be enjoyed. However, quick lime charged in the early stage of blowing is a fine particle of 3.35 to 9.5 mm. The phosphorus removal rate was improved from 101, and it was possible to produce a low phosphorus steel having a P concentration of 0.015% or less at the end of blowing.
また、吹錬全期間の９０〜１００％が経過している間に装入塩基度が０．６％上昇するように細粒生石灰を装入したサンプルＮｏ．３は、吹錬全期間の９０〜１００％が経過している間に装入塩基度が０．５％上昇するように細粒生石灰を装入したサンプルＮｏ．１４よりも、吹錬終了時における溶鋼中のＰ濃度は高かった。吹錬全期間の９０〜１００％が経過している間に装入する生石灰量が多過ぎると、生石灰がスラグ中の限られた量のＦｅＯを奪い合う形になってしまい、結果として生石灰がＦｅＯと反応して溶解しきれず、Ｐ濃度が十分に低下しなかったと考えられる。 In addition, sample No. 1 was charged with fine-grained quicklime so that the charging basicity increased by 0.6% while 90 to 100% of the entire blowing period had elapsed. 3 is sample No. 3 in which fine quicklime was charged so that the charging basicity increased by 0.5% while 90 to 100% of the entire blowing period had elapsed. The P concentration in the molten steel at the end of blowing was higher than 14. If too much lime is charged while 90 to 100% of the entire blowing period has elapsed, the quick lime will compete for a limited amount of FeO in the slag, resulting in quick lime being FeO. It is considered that the P concentration was not sufficiently lowered due to the reaction with the solution.
（７）生石灰の追加装入の有無の差
サンプルＮｏ．１、１５、１７及び１９は、それぞれ吹錬開始前または開始直後に細粒生石灰を全量装入し、吹錬終了時における溶鋼中のＣ濃度が０．０５〜０．５０％となっている例である。一方、サンプルＮｏ．４、１６、１８及び２０は、それぞれＣ濃度が対比するサンプルと同じ条件で吹錬全期間の９０〜１００％が経過している間に生石灰を装入した例である。これらのサンプルを比較すると、吹錬開始前または開始直後に細粒生石灰を全量装入するよりも、吹錬全期間の９０〜１００％が経過している間に細粒生石灰を装入した方が、吹錬終了時における溶鋼中のＰ濃度は低かった。この条件下では、スラグ中のＦｅＯ濃度が、本発明の効果を発揮できる程度に存在していたためと考えられる。
(7) Difference in presence or absence of additional charging of quicklime Sample No. 1, 15, 17 and 19 are charged with the entire amount of fine lime before or immediately after the start of blowing, and the C concentration in the molten steel at the end of blowing is 0.05 to 0.50%. It is an example. On the other hand, sample No. 4, 16, 18 and 20 are examples in which quick lime was charged while 90 to 100% of the total blowing period had elapsed under the same conditions as the sample with which the C concentration was compared. Comparing these samples, those who charged fine quicklime during 90-100% of the total duration of blowing, rather than charging the whole amount of fine quicklime before or immediately after the start of blowing However, the P concentration in the molten steel at the end of blowing was low. This is probably because the FeO concentration in the slag was present to such an extent that the effects of the present invention can be exhibited.
（８）溶鋼中のＣ濃度の差
サンプルＮｏ．１０６及び１０７は、吹錬終了時における溶鋼中のＣ濃度を０．６％とした場合である。吹錬開始前または開始直後に細粒生石灰を全量添加した場合サンプルＮｏ．１０６、及び吹錬全期間の９０〜１００％が経過している間に装入塩基度が０．３上昇するように細粒生石灰を追加装入したサンプルＮｏ．１０７は、吹錬終了時における溶鋼中のＰ濃度はどちらも０．０１７％と高く、低りん鋼を溶製できなかった。吹錬終了点における溶鋼中のＣ濃度が高過ぎると、スラグ中のＦｅＯ濃度が低くなり、吹錬全期間の９０〜１００％が経過している間に装入した生石灰の気孔中へスラグが侵入してＣａＯ固相壁へＦｅＯが浸潤するのが間に合わず、未溶解部分が残留してしまったために、脱りんに十分寄与できなかったと考えられる。
(8) Difference in C concentration in molten steel Sample No. 106 and 107 are cases where the C concentration in the molten steel at the end of blowing is 0.6%. When all the fine lime is added before or immediately after the start of blowing, sample No. 106, and sample No. 1 in which fine granule lime was additionally charged so that the charging basicity increased by 0.3 while 90 to 100% of the entire blowing period had elapsed. In No. 107, the P concentration in the molten steel at the end of the blowing was as high as 0.017%, and low phosphorus steel could not be produced. If the C concentration in the molten steel at the end of blowing is too high, the FeO concentration in the slag will be low, and slag will enter into the pores of the quick lime charged while 90-100% of the entire blowing period has elapsed. The intrusion and infiltration of FeO into the CaO solid phase wall was not in time, and the undissolved portion remained, so it was considered that the dephosphorization could not be sufficiently contributed.
また、サンプルＮｏ．１０８〜１１０は、吹錬終了時における溶鋼中のＣ濃度が０．０３％と低い場合である。サンプルＮｏ．１０８は、１０〜３０ｍｍの生石灰を吹錬前に全量装入した例であり、サンプルＮｏ．１０９は、吹錬全期間の０〜１０％が経過している間に細粒生石灰を追加で装入した例であり、サンプルＮｏ．１１０は、吹錬全期間の９０〜１００％が経過している間に細粒生石灰を追加で装入した例である。これらのサンプルはいずれも、吹錬終了時における溶鋼中のＰ濃度に差は生じなかった。吹錬末期における溶鋼中のＣ濃度が０．０５％未満になると、スラグ中においてＦｅＯ濃度が急上昇するため、装入した生石灰の溶解が急速に進み、吹錬末期に添加した細粒生石灰もカルシウムフェライトとして脱りんに寄与する前に周囲のスラグへ均一分散して溶解してしまったと考えられる。そのため、溶鋼中のＰ濃度の低減には特別な効果が無かったと考えられる。 Sample No. 108 to 110 are cases where the C concentration in the molten steel at the end of blowing is as low as 0.03%. Sample No. No. 108 is an example in which 10 to 30 mm of quicklime is charged in its entirety before blowing. 109 is an example in which fine quicklime was additionally charged while 0 to 10% of the entire blowing period had elapsed. 110 is an example in which fine-grained quicklime is additionally charged while 90 to 100% of the entire blowing period has elapsed. None of these samples produced a difference in the P concentration in the molten steel at the end of blowing. When the C concentration in the molten steel at the end of blowing is less than 0.05%, the FeO concentration rises rapidly in the slag, so the dissolution of the charged quicklime proceeds rapidly, and the fine quicklime added at the end of blowing is also calcium. It is thought that the ferrite was uniformly dispersed and dissolved in the surrounding slag before contributing to dephosphorization. Therefore, it is considered that there was no special effect in reducing the P concentration in the molten steel.
（実施例１）
まず、Ｓｉ濃度が０．３％で、Ｐ濃度が０．１０％である溶銑２７０ｔとスクラップ２０ｔとを転炉へ装入した。そして、副原料して、スケール３ｔ、ＣａＯ源である粒径３．３５〜９．５ｍｍの生石灰（ＣａＯ約９５％）１４．５ｋｇ／ｔ、およびＭｇＯ源である粒径３．３５〜９．５ｍｍの軽焼ドロマイト（ＣａＯ約６０％、ＭｇＯ約３４％）１３ｋｇ／ｔを添加して初期装入塩基度を３．３とした。なお、これらの副原料は吹錬開始後０．５分間以内に転炉内に投入し、吹錬の条件は、上吹き酸素流量６００００Ｎｍ3／ｈ、底吹きＣＯ2流量２０００Ｎｍ3／ｈとした。その後は、ＣａＯ含有副原料は一切投入せずに吹錬を行った。その結果、吹錬終了時の溶鋼の温度は１６４５℃であり、Ｃ濃度は０．１％、Ｐ濃度は０．０１５％だった。以上のように、目標とするＰ濃度を０．０１５％以下とする低りん鋼を溶製することができた。
Example 1
First, hot metal 270t and scrap 20t having a Si concentration of 0.3% and a P concentration of 0.10% were charged into a converter. And as auxiliary materials, scale 3t, CaO source particle size 3.35 to 9.5 mm quicklime (CaO about 95%) 14.5 kg / t, and MgO source particle size 3.35-9. 5 kg of lightly burned dolomite (CaO about 60%, MgO about 34%) 13 kg / t was added to make the initial charge basicity 3.3. These auxiliary materials were put into the converter within 0.5 minutes after the start of blowing, and the blowing conditions were an upper blowing oxygen flow rate of 60000 Nm 3 / h and a bottom blowing CO 2 flow rate of 2000 Nm 3 / h. . Thereafter, blowing was performed without adding any CaO-containing auxiliary material. As a result, the temperature of the molten steel at the end of blowing was 1645 ° C., the C concentration was 0.1%, and the P concentration was 0.015%. As described above, a low phosphorus steel having a target P concentration of 0.015% or less could be produced.
一方、比較例として、まず、Ｓｉ濃度が０．３％、Ｐ濃度が０．１０％の溶銑２７０ｔとスクラップ２０ｔとを転炉へ装入した。そして、副原料として、スケール３ｔ、ＣａＯ源である粒径１０〜３０ｍｍの生石灰（ＣａＯ約９５％）１４．５ｋｇ／ｔ、およびＭｇＯ源である軽焼ドロマイト（ＣａＯ約６０％、ＭｇＯ約３４％）１３ｋｇ／ｔを添加して初期装入塩基度を３．３とした。なお、これらの副原料は吹錬開始後０．５分間以内に転炉内に投入し、吹錬の条件は、上吹き酸素流量６００００Ｎｍ3／ｈ、底吹きＣＯ2流量２０００Ｎｍ3／ｈとした。その後は、ＣａＯ含有副原料は一切投入せずに吹錬を行った。その結果、吹錬終了時の溶鋼の温度は１６４５℃であり、Ｃ濃度は０．１％、Ｐ濃度は０．０１９％であった。以上のように、目標とするＰ濃度を０．０１５％以下とする低りん鋼を溶製することができなかった。 On the other hand, as a comparative example, first, hot metal 270t and scrap 20t having a Si concentration of 0.3% and a P concentration of 0.10% were charged into a converter. As auxiliary materials, scale 3t, quick lime with a particle size of 10 to 30 mm as CaO source (CaO about 95%) 14.5 kg / t, and light burned dolomite as MgO source (CaO about 60%, MgO about 34%) ) 13 kg / t was added to make the initial charge basicity 3.3. These auxiliary materials were put into the converter within 0.5 minutes after the start of blowing, and the blowing conditions were an upper blowing oxygen flow rate of 60000 Nm 3 / h and a bottom blowing CO 2 flow rate of 2000 Nm 3 / h. . Thereafter, blowing was performed without adding any CaO-containing auxiliary material. As a result, the temperature of the molten steel at the end of blowing was 1645 ° C., the C concentration was 0.1%, and the P concentration was 0.019%. As described above, a low phosphorus steel with a target P concentration of 0.015% or less could not be produced.
（実施例２）
まず、Ｓｉ濃度が０．３％、Ｐ濃度が０．１０％である溶銑２７０ｔとスクラップ２０ｔとを転炉へ装入した。そして、副原料として、スケール３ｔ、ＣａＯ源である粒径３．３５〜９．５ｍｍの生石灰（ＣａＯ約９５％）１４．５ｋｇ／ｔ、およびＭｇＯ源である粒径３．３５〜９．５ｍｍの軽焼ドロマイト（ＣａＯ約６０％、ＭｇＯ約３４％）１３ｋｇ／ｔを添加した。具体的には、これらの副原料のうち、生石灰１２．５ｋｇ／ｔ、軽焼ドロマイト１３ｋｇ／ｔを吹錬開始直前に転炉内に投入して初期装入塩基度を３．０とした。そして、上吹き酸素流量６００００Ｎｍ3／ｈ、底吹きＣＯ2流量２０００Ｎｍ3／ｈの条件で吹錬を開始し、吹錬全期間の０〜１０％が経過している間に粒径が３．３５〜９．５ｍｍの生石灰を、装入塩基度が０．３増加する分（２ｋｇ／ｔ）だけ添加し、その後はＣａＯ含有副原料を一切投入せずに吹錬を終了した。吹錬終了時における溶鋼の温度は１６４５℃であり、Ｃ濃度は０．１％、Ｐ濃度は０．０１５％だった。以上のように、目標とするＰ濃度を０．０１５％以下とする低りん鋼を溶製することができた。
(Example 2)
First, hot metal 270t and scrap 20t having a Si concentration of 0.3% and a P concentration of 0.10% were charged into a converter. As auxiliary materials, scale 3t, CaO source particle size 3.35 to 9.5 mm quick lime (CaO about 95%) 14.5 kg / t, and MgO source particle size 3.35 to 9.5 mm 13 kg / t of light burned dolomite (CaO about 60%, MgO about 34%) was added. Specifically, among these auxiliary materials, quick lime 12.5 kg / t and light calcined dolomite 13 kg / t were put into the converter immediately before the start of blowing and the initial charge basicity was set to 3.0. Then, blowing was started under conditions of an upper blowing oxygen flow rate of 60000 Nm 3 / h and a bottom blowing CO 2 flow rate of 2000 Nm 3 / h. 35 to 9.5 mm of quicklime was added for an amount (2 kg / t) in which the charging basicity increased by 0.3, and thereafter, blowing was completed without adding any CaO-containing auxiliary material. The temperature of the molten steel at the end of blowing was 1645 ° C., the C concentration was 0.1%, and the P concentration was 0.015%. As described above, a low phosphorus steel having a target P concentration of 0.015% or less could be produced.
（実施例３）
まず、Ｓｉ濃度が０．３％、Ｐ濃度が０．１１％の溶銑２７０ｔとスクラップ２０ｔとを転炉へ装入した。そして、副原料として、スケール３ｔ、ＣａＯ源である粒径３．３５〜９．５ｍｍの生石灰（ＣａＯ約９５％）１２．５ｋｇ／ｔ、およびＭｇＯ源である粒径３．３５〜９．５ｍｍの軽焼ドロマイト（ＣａＯ約６０％、ＭｇＯ約３４％）１３ｋｇ／ｔを添加して初期装入塩基度を３．０とした。なお、これらの副原料は吹錬開始後０．５分間以内に転炉内に投入し、吹錬の条件は、上吹き酸素流量６００００Ｎｍ3／ｈ、底吹きＣＯ2流量２０００Ｎｍ3／ｈとした。その後は、吹錬全期間の９０％が経過するまではＣａＯ含有副原料は一切投入せずに、吹錬を行った。そして、吹錬全期間の９０〜１００％が経過している間に粒径が３．３５〜９．５ｍｍの生石灰を、装入塩基度が初期装入塩基度から０．３増加する分（２ｋｇ／ｔ）だけ添加した。その結果、吹錬終了時の溶鋼の温度は１６５０℃であり、Ｃ濃度は０．１％、Ｐ濃度は０．０１４％であった。このように、粒径範囲が３．３５〜９．５ｍｍの生石灰を吹錬初期に全て装入した例（実施例１）より、Ｐ濃度をさらに低減することができた。
(Example 3)
First, hot metal 270t and scrap 20t having a Si concentration of 0.3% and a P concentration of 0.11% were charged into a converter. As auxiliary materials, scale 3t, CaO source particle size 3.35 to 9.5 mm quicklime (CaO about 95%) 12.5 kg / t, and MgO source particle size 3.35 to 9.5 mm Lightly charged dolomite (CaO about 60%, MgO about 34%) 13 kg / t was added to adjust the initial charge basicity to 3.0. These auxiliary materials were put into the converter within 0.5 minutes after the start of blowing, and the blowing conditions were an upper blowing oxygen flow rate of 60000 Nm 3 / h and a bottom blowing CO 2 flow rate of 2000 Nm 3 / h. . Thereafter, until 90% of the entire blowing period had elapsed, no additional CaO-containing auxiliary material was blown, and blowing was performed. And while 90 to 100% of the entire blowing period has elapsed, quick lime having a particle size of 3.35 to 9.5 mm is added to the amount by which the charging basicity is increased by 0.3 from the initial charging basicity ( Only 2 kg / t) was added. As a result, the temperature of the molten steel at the end of blowing was 1650 ° C., the C concentration was 0.1%, and the P concentration was 0.014%. Thus, the P concentration could be further reduced from the example (Example 1) in which quick lime having a particle size range of 3.35 to 9.5 mm was completely charged in the initial stage of blowing.
（実施例４）
まず、Ｓｉ濃度が０％、Ｐ濃度が０．０３％の脱りん溶銑２７０ｔを転炉へ装入した。そして、副原料として、ＣａＯ源である粒径３．３５〜９．５ｍｍの生石灰（ＣａＯ約９５％）１２．５ｋｇ／ｔ、ＭｇＯ源である粒径３．３５〜９．５ｍｍの軽焼ドロマイト（ＣａＯ約６０％、ＭｇＯ約３４％）１３ｋｇ／ｔ、およびＳｉＯ2源である粒径３．３５〜９．５ｍｍの珪石６．４ｋｇ／ｔを添加した。具体的には、これらの副原料のうち、生石灰１０．５ｋｇ／ｔ、軽焼ドロマイト１３ｋｇ／ｔ、および珪石６．４ｋｇ／ｔを吹錬開始直前に転炉内に投入して初期装入塩基度を３．０とした。そして、上吹き酸素流量６００００Ｎｍ3／ｈ、底吹きＣＯ2流量２０００Ｎｍ3／ｈの条件で吹錬を開始して、吹錬全期間の０〜１０％が経過している間に粒径が３．３５〜９．５ｍｍの生石灰を、装入塩基度が初期装入塩基度から０．３増加する分（２ｋｇ／ｔ）だけ添加し、その後はＳｉＯ2やＣａＯ含有副原料を一切投入せずに吹錬を終了した。吹錬終了時における溶鋼の温度は１６５５℃であり、Ｃ濃度は０．２％、Ｐ濃度は０．００９％であった。
Example 4
First, 270 t of dephosphorized hot metal having a Si concentration of 0% and a P concentration of 0.03% was charged into the converter. And, as auxiliary materials, quick lime (CaO about 95%) 12.5 kg / t with a particle size of 3.35 to 9.5 mm as a CaO source, light burned dolomite with a particle size of 3.35 to 9.5 mm as a MgO source (CaO about 60%, MgO about 34%) 13 kg / t, and 6.4 kg / t of silica stone having a particle size of 3.35 to 9.5 mm as a SiO 2 source were added. Specifically, among these auxiliary materials, quick lime 10.5 kg / t, light calcined dolomite 13 kg / t, and silica 6.4 kg / t are put into the converter immediately before the start of blowing and the initial charge base is used. The degree was set to 3.0. Then, the blowing was started under the conditions of a top blowing oxygen flow rate of 60000 Nm 3 / h and a bottom blowing CO 2 flow rate of 2000 Nm 3 / h, and the particle size was 3 while 0 to 10% of the entire blowing time had elapsed. Add 35 to 9.5mm quicklime for the amount of basic charge increased by 0.3 from the initial basic charge (2kg / t), and then do not add any SiO 2 or CaO-containing auxiliary materials Finished blowing. The temperature of the molten steel at the end of blowing was 1655 ° C., the C concentration was 0.2%, and the P concentration was 0.009%.
（実施例５）
まず、Ｓｉ濃度が０％、Ｐ濃度が０．０３％の脱りん溶銑２７０ｔを転炉へ装入した。そして、副原料として、ＣａＯ源である粒径３．３５〜９．５ｍｍの生石灰（ＣａＯ約９５％）１２．５ｋｇ／ｔ、ＭｇＯ源である粒径３．３５〜９．５ｍｍの軽焼ドロマイト（ＣａＯ約６０％、ＭｇＯ約３４％）１３ｋｇ／ｔ、およびＳｉＯ2源である粒径３．３５〜９．５ｍｍの珪石６．４ｋｇ／ｔを添加して初期装入塩基度を３．０とした。なお、これらの副原料は吹錬開始後０．５分間以内に転炉内に投入し、吹錬の条件は、上吹き酸素流量６００００Ｎｍ3／ｈ、底吹きＣＯ2流量２０００Ｎｍ3／ｈとした。その後は、吹錬全期間の９０％が経過するまではＣａＯ含有副原料は一切投入せずに吹錬を行った。そして、吹錬全期間の９０〜１００％が経過している間に粒径が３．３５〜９．５ｍｍの生石灰を装入塩基度が初期装入塩基度から０．３増加する分（２ｋｇ／ｔ）だけ添加した。その結果、吹錬終了時における溶鋼の温度は１６６０℃であり、Ｃ濃度は０．２％、Ｐ濃度は０．００７％であった。以上のように極めて低いＰ濃度まで脱りんすることができた。
(Example 5)
First, 270 t of dephosphorized hot metal having a Si concentration of 0% and a P concentration of 0.03% was charged into the converter. And, as auxiliary materials, quick lime (CaO about 95%) 12.5 kg / t with a particle size of 3.35 to 9.5 mm as a CaO source, light burned dolomite with a particle size of 3.35 to 9.5 mm as a MgO source (CaO about 60%, MgO about 34%) 13 kg / t, and 6.4 kg / t of silica stone having a particle size of 3.35 to 9.5 mm, which is a SiO 2 source, was added to adjust the initial charge basicity to 3.0. It was. These auxiliary materials were put into the converter within 0.5 minutes after the start of blowing, and the blowing conditions were an upper blowing oxygen flow rate of 60000 Nm 3 / h and a bottom blowing CO 2 flow rate of 2000 Nm 3 / h. . After that, until 90% of the entire blowing period passed, blowing was performed without adding any CaO-containing auxiliary materials. And while 90 to 100% of the whole blowing period has elapsed, the amount of the charged basicity increased by 0.3 from the initial charged basicity of quick lime having a particle size of 3.35 to 9.5 mm (2 kg) / T) was added. As a result, the temperature of the molten steel at the end of blowing was 1660 ° C., the C concentration was 0.2%, and the P concentration was 0.007%. As described above, it was possible to dephosphorize to a very low P concentration.
Claims (4)
上底吹き転炉へＳｉ濃度が０．２５〜０．６質量％の溶銑を装入する工程と、
吹錬全期間の１０％が経過するまでに装入するＣａＯの質量のＳｉＯ2の質量に対する割合を表す初期装入塩基度が３．０以上４．５以下となるように、前記溶銑が装入された転炉へ副原料を装入して吹錬する工程とを有し、
前記転炉へ装入する副原料としてのＣａＯ源及びＭｇＯ源は、粒径を３．３５〜９．５ｍｍとし、
前記吹錬全期間の１０％が経過した後には、当該ＣａＯ源及びＭｇＯ源を前記転炉へ一切装入しないことを特徴とする転炉操業方法。 A converter operating method for melting low phosphorus steel having a C concentration of 0.05 to 0.5 mass% in molten steel,
A step of charging molten iron having a Si concentration of 0.25 to 0.6% by mass into the top-bottom blowing converter;
The molten iron is charged so that the initial charge basicity, which represents the ratio of the mass of CaO charged to the mass of SiO 2 by 10% of the total blowing period, is 3.0 or more and 4.5 or less. and a blowing refining to that step was charged auxiliary materials to incoming been converter,
The CaO source and MgO source as auxiliary materials charged into the converter have a particle size of 3.35 to 9.5 mm,
After 10% of the entire blowing period has elapsed, the converter operating method is characterized in that the CaO source and the MgO source are not charged into the converter at all.
上底吹き転炉へＳｉ濃度が０．０２質量％以下の脱りん溶銑を装入する工程と、
吹錬全期間の１０％が経過するまでに装入するＣａＯの質量のＳｉＯ2の質量に対する割合を表す初期装入塩基度が３．０以上４．５以下となるように、前記脱りん溶銑が装入された転炉へ副原料を装入して吹錬する工程とを有し、
前記転炉へ装入する副原料としてのＣａＯ源、ＭｇＯ源、及びＳｉＯ2源は、粒径を３．３５〜９．５ｍｍとし、
前記吹錬全期間の１０％が経過した後には、当該ＣａＯ源、ＭｇＯ源、及びＳｉＯ2源を前記転炉へ一切装入しないことを特徴とする転炉操業方法。 A converter operating method for melting low phosphorus steel having a C concentration of 0.05 to 0.5 mass% in molten steel,
Charging a dephosphorized hot metal having a Si concentration of 0.02% by mass or less into an upper bottom blowing converter;
The dephosphorized hot metal is prepared so that the initial charging basicity representing the ratio of the mass of CaO to the mass of SiO 2 is 3.0 or more and 4.5 or less until 10% of the entire blowing period elapses. There and a blowing refining to that step was charged auxiliary materials to the converter that has been charged,
The CaO source, the MgO source, and the SiO 2 source as auxiliary materials charged into the converter have a particle size of 3.35 to 9.5 mm,
The converter operating method is characterized in that the CaO source, MgO source, and SiO 2 source are not charged into the converter at all after 10% of the entire blowing period has elapsed.
前記吹錬の全期間の９０〜１００％が経過している間に、粒径３．３５〜９．５ｍｍの生石灰を、前記初期装入塩基度よりも０．１以上０．５以下の範囲で高くなる量だけ装入することを特徴とする請求項１に記載の転炉操業方法。 After 10% of the entire blowing period has elapsed, instead of charging the converter with no CaO source and MgO source,
While 90 to 100% of the entire period of the blowing has elapsed, quick lime having a particle size of 3.35 to 9.5 mm is in a range of 0.1 to 0.5 than the initial charging basicity. The converter operation method according to claim 1, wherein the charging is performed in an amount that increases at a high rate.
前記吹錬の全期間の９０〜１００％が経過している間に、粒径３．３５〜９．５ｍｍの生石灰を、前記初期装入塩基度よりも０．１以上０．５以下の範囲で高くなる量だけ装入することを特徴とする請求項２に記載の転炉操業方法。 After 10% of the entire blowing period has elapsed, instead of charging the CaO source, MgO source, and SiO 2 source into the converter at all,
While 90 to 100% of the entire period of the blowing has elapsed, quick lime having a particle size of 3.35 to 9.5 mm is in a range of 0.1 to 0.5 than the initial charging basicity. The converter operation method according to claim 2, wherein the charging is performed in an amount that increases by a large amount.
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