JP2022160777A - Smelting method of low phosphorus steel - Google Patents
Smelting method of low phosphorus steel Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 38
- 239000010959 steel Substances 0.000 title claims abstract description 38
- 229910052698 phosphorus Inorganic materials 0.000 title claims abstract description 22
- 239000011574 phosphorus Substances 0.000 title claims abstract description 22
- 238000000034 method Methods 0.000 title claims abstract description 19
- 238000003723 Smelting Methods 0.000 title claims abstract description 10
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 title abstract description 11
- 238000007664 blowing Methods 0.000 claims abstract description 121
- 238000005261 decarburization Methods 0.000 claims abstract description 96
- 239000002893 slag Substances 0.000 claims abstract description 63
- 235000008733 Citrus aurantifolia Nutrition 0.000 claims abstract description 57
- 235000011941 Tilia x europaea Nutrition 0.000 claims abstract description 57
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 57
- 239000004571 lime Substances 0.000 claims abstract description 57
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 57
- 239000001301 oxygen Substances 0.000 claims abstract description 57
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 39
- 239000002253 acid Substances 0.000 claims abstract description 19
- 229910052742 iron Inorganic materials 0.000 claims abstract description 18
- 238000002844 melting Methods 0.000 claims description 4
- 230000008018 melting Effects 0.000 claims description 4
- 238000007670 refining Methods 0.000 claims description 2
- 230000008859 change Effects 0.000 abstract description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 abstract 2
- 229910000019 calcium carbonate Inorganic materials 0.000 abstract 1
- 235000010216 calcium carbonate Nutrition 0.000 abstract 1
- 239000002184 metal Substances 0.000 description 21
- 229910052751 metal Inorganic materials 0.000 description 21
- 230000007423 decrease Effects 0.000 description 15
- 239000007791 liquid phase Substances 0.000 description 14
- 238000006243 chemical reaction Methods 0.000 description 13
- 238000010586 diagram Methods 0.000 description 10
- 230000000694 effects Effects 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 7
- 239000003795 chemical substances by application Substances 0.000 description 4
- 230000007704 transition Effects 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000006722 reduction reaction Methods 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910005347 FeSi Inorganic materials 0.000 description 1
- 229910000677 High-carbon steel Inorganic materials 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 239000012159 carrier gas Substances 0.000 description 1
- 229910052681 coesite Inorganic materials 0.000 description 1
- 229910052906 cristobalite Inorganic materials 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000002250 progressing effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000010079 rubber tapping Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 229910052682 stishovite Inorganic materials 0.000 description 1
- 229910052905 tridymite Inorganic materials 0.000 description 1
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- 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
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Abstract
Description
本発明は、脱炭吹錬中の脱燐効率を向上させた低燐鋼の溶製方法に関する。 TECHNICAL FIELD The present invention relates to a method for smelting low-phosphorus steel with improved dephosphorization efficiency during decarburization blowing.
従来、溶銑中のPを除去するために脱燐吹錬が行われているが、低燐鋼を溶製する場合には、その後の脱炭吹錬においてもPを効率的に除去することが重要である。また、脱燐スラグからの復燐を防止するために、脱炭吹錬を行う前に脱燐スラグをできるだけ除去する必要がある。ただし、一部の脱燐スラグは持ち越しスラグとして残存するため、復燐防止のために脱炭吹錬を行う前に新規に石灰源を投入してスラグの塩基度を調整した場合、石灰が過剰になりスラグの液相率が低下する。その結果、脱燐速度が過度に遅くなることから、脱炭吹錬中は脱燐効率が低く、十分に脱燐を行うことができない。 Conventionally, dephosphorization blowing is performed to remove P from hot metal. However, in the case of smelting low-phosphorus steel, it is possible to efficiently remove P in the subsequent decarburization blowing. is important. In addition, in order to prevent phosphorus reversion from the dephosphorization slag, it is necessary to remove the dephosphorization slag as much as possible before decarburization blowing. However, since some of the dephosphorization slag remains as carryover slag, if a new lime source is added to adjust the basicity of the slag before decarburization blowing is performed to prevent replenishment of phosphorus, excess lime will be generated. and the liquid phase ratio of the slag decreases. As a result, the dephosphorization rate becomes excessively slow, so the dephosphorization efficiency is low during decarburization blowing, and sufficient dephosphorization cannot be achieved.
そこで、効率よく脱燐処理を行うために様々な提案がなされている。特許文献1には、吹錬時期に応じて送酸速度を変更したりCaO源を装入したりする技術が開示されている。特許文献2には、酸素の吹込み開始前後に第一スラグ剤を装入し、脱炭吹錬中に第二スラグ剤を、キャリアガスを用いて吹込む方法が開示されている。
Therefore, various proposals have been made for efficient dephosphorization.
しかしながら、上述の特許文献1に記載の技術では、スラグの溶解を優先して、吹錬開始時のスラグ塩基度を通常の低燐向け転炉プロセスの脱炭吹錬におけるスラグ塩基度と比較して過度に下げており、吹錬初期のスラグの脱燐能が大きく低下してしまう。これにより、吹錬中盤で追装するCaO源が過剰となり、吹錬中に十分溶解し切らず、安定した低燐化効果が得られない。特許文献2に記載の技術は、脱炭吹錬にて第二スラグ剤上吹きを実施するための設備改造が必要となる。また、第二スラグ剤上吹き時のキャリアとなる窒素ガスにより溶鉄中のN濃度が高くなるため、低窒素鋼へ適用する際には吹き込み時期の制約がある。
However, in the technique described in
本発明は前述の問題点を鑑み、簡便な操作で脱炭吹錬中の脱燐効率をより向上させた低燐鋼の溶製方法を提供することを目的とする。 SUMMARY OF THE INVENTION It is an object of the present invention to provide a low-phosphorus steel smelting method in which dephosphorization efficiency during decarburization blowing is improved by a simple operation.
脱炭吹錬を行う前に脱燐スラグを分離して新規に石灰源を投入した場合、石灰が過剰となりスラグ液相率が低下する。その結果、脱炭吹錬中期までの脱燐速度が過度に遅くなり、かつ持ち越しスラグからの復燐が生じる。一方で、脱炭吹錬末期では、溶鉄中のC濃度が下がりにくくなってFeOが多量に生成される。FeOが多量に生成されると、スラグの液相率が上昇し、脱燐反応が起こりやすくなる一方で、鉄の歩留まりという観点から脱炭吹錬末期の時間を過度に延ばすことができない。 If the dephosphorization slag is separated before decarburization blowing and a new lime source is added, the lime becomes excessive and the slag liquid fraction decreases. As a result, the dephosphorization rate becomes excessively slow until the middle stage of decarburization blowing, and phosphorus reversion from the carried-over slag occurs. On the other hand, in the final stage of decarburization blowing, the C concentration in the molten iron is difficult to decrease, and a large amount of FeO is produced. When a large amount of FeO is produced, the liquid phase ratio of the slag increases and the dephosphorization reaction tends to occur.
そこで、本発明者らは、脱炭吹錬の末期までの間はスラグの液相率を確保し、歩留まりの低下を抑制しつつ吹錬末期の時間を多く確保できれば脱燐効率が上昇すると考え、吹錬開始時点で石灰源の投入量を抑制し、かつ脱炭吹錬末期に残りの石灰源を投入しつつ、送酸速度を低下させることを見出し、本発明に至った。 Therefore, the present inventors believe that the dephosphorization efficiency will increase if the liquid phase ratio of the slag can be secured until the end of the decarburization blowing, and a longer time can be secured at the end of the blowing while suppressing the decrease in yield. We have found that the amount of lime source input is suppressed at the start of blowing, and the remaining lime source is added at the end of decarburization blowing, and the oxygen transfer rate is reduced, leading to the present invention.
本発明は以下の通りである。
(1)
上吹きランスを具備した転炉型精錬装置において、脱燐吹錬を実施して生成した脱燐スラグを分離した後に、CaOまたはCaCO3を含む石灰源を全CaO換算質量で30~70kg/t-steelの範囲で投入して脱炭吹錬を実施し、溶鉄中のC濃度を0.4質量%未満まで低減させる低燐鋼の溶製方法であって、
前記脱炭吹錬において、吹錬を開始する時点で前記石灰源を前記全CaO換算質量の60~80%投入し、前記上吹きランスから送酸速度が150~250Nm3/(h・t-steel)の範囲で酸素を吹き付けて吹錬を開始し、吹錬開始時点から総酸素量中の流量割合で80~90%の酸素を供給した時点において、前記石灰源の残りを投入するとともに送酸速度を(1)式の範囲に変更することを特徴とする、低燐鋼の溶製方法。
0.40≦FO2_after/FO2_before≦0.85 ・・・(1)
ここで、FO2_before:前記石灰源の残りを投入するとともに送酸速度を変更する前の送酸速度(Nm3/(h・t-steel))、FO2_after:前記石灰源の残りを投入するとともに送酸速度を変更した後の送酸速度(Nm3/(h・t-steel))である。
The present invention is as follows.
(1)
After separating the dephosphorization slag produced by dephosphorization blowing in a converter type refining apparatus equipped with a top blowing lance, a lime source containing CaO or CaCO 3 is added at a total CaO equivalent mass of 30 to 70 kg / t. - A low-phosphorus steel smelting method in which decarburization blowing is performed by charging in the steel range and the C concentration in the molten iron is reduced to less than 0.4% by mass,
In the decarburization blowing, 60 to 80% of the total CaO-equivalent mass of the lime source is introduced at the start of blowing, and the oxygen feed rate is 150 to 250 Nm 3 /(ht- Steel) is blown to start blowing, and when oxygen is supplied at a rate of 80 to 90% of the total oxygen amount from the start of blowing, the rest of the lime source is added and fed. A method for melting low-phosphorus steel, characterized by changing the acid rate to the range of formula (1).
0.40≦F 02_after /F 02_before ≦0.85 (1)
Here, F O2_before : the acid supply rate (Nm 3 /(h·t-steel)) before the rest of the lime source is added and the acid supply rate is changed, F O2_after : the rest of the lime source is added and the acid feed rate (Nm 3 /(h·t-steel)) after changing the acid feed rate.
本発明によれば、脱炭吹錬中の脱燐効率をより向上させた低燐鋼の溶製方法を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the smelting method of the low phosphorus steel which further improved the dephosphorization efficiency during decarburization blowing can be provided.
以下、本発明の実施形態について、図面を参照しながら説明する。ここで、本発明で溶製する低燐鋼は、P濃度が0.01質量%以下の鋼である。 BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, the low-phosphorus steel melted in the present invention is steel having a P concentration of 0.01% by mass or less.
まず、脱炭吹錬を行う前に溶銑の脱燐吹錬を行い、溶銑中のP濃度を予め低下させておく。脱炭吹錬前の脱燐吹錬では、例えば溶銑中のP濃度を0.04質量%以下にすることが好ましい。脱燐吹錬後は、脱燐吹錬によって生じた脱燐スラグと溶銑とを分離する。脱燐吹錬後の溶銑と脱燐スラグとの分離方法については特に限定しないが、低燐鋼向け転炉吹錬プロセスでは脱燐スラグと溶銑とを可能な限り分離する必要がある。そこで、なるべくスラグを持ち越さない方法として、例えば溶銑を出湯した後に脱燐スラグを排滓し、出湯した溶銑を再びその転炉に装入する方法が挙げられる。これらの方法により脱燐スラグを90%以上分離しておくことが好ましい。 First, before performing decarburization blowing, hot metal is subjected to dephosphorization blowing to reduce the P concentration in the hot metal in advance. In dephosphorization blowing before decarburization blowing, for example, it is preferable to set the P concentration in the hot metal to 0.04% by mass or less. After the dephosphorization blowing, the dephosphorization slag generated by the dephosphorization blowing is separated from the hot metal. The method of separating the dephosphorization slag from the hot metal after dephosphorization blowing is not particularly limited, but in the converter blowing process for low phosphorus steel, it is necessary to separate the dephosphorization slag and the hot metal as much as possible. Therefore, as a method for keeping the slag as little as possible, for example, after tapping the hot metal, the dephosphorization slag is discharged, and the tapped hot metal is charged into the converter again. It is preferable to separate 90% or more of the dephosphorization slag by these methods.
そして、脱燐スラグを分離した後に、CaOまたはCaCO3を含む石灰源を転炉に投入して脱炭吹錬を開始する。本実施形態では、詳細は後述するが、脱炭吹錬の中期までは、脱炭スラグの液相率を確保して脱燐反応を促進し、さらにFeOが多く生成する脱炭吹錬末期では、鉄の歩留まりの低下を抑制しつつ脱燐反応の時間をなるべく確保するようにする。 After separating the dephosphorization slag, a lime source containing CaO or CaCO 3 is put into the converter to start decarburization blowing. In this embodiment, the details will be described later, but until the middle of the decarburization blowing, the liquid phase ratio of the decarburization slag is secured to promote the dephosphorization reaction, and furthermore, at the end of the decarburization blowing where a large amount of FeO is generated , to secure the time for the dephosphorization reaction as much as possible while suppressing the decrease in the yield of iron.
図1は、脱炭吹錬中の溶鉄中P濃度の推移を説明するための図である。脱燐吹錬によって生じた脱燐スラグの一部が不可避的に持ち越しスラグとして残存することになる。前述のように脱燐スラグと溶銑とを可能な限り分離するため、脱炭スラグでは持ち越しスラグを含むもののSiO2分が少なくなり、石灰源の過剰投入により脱炭が進行する脱炭吹錬中期までは脱炭スラグの液相率が低下し、脱燐速度が過度に遅くなる。したがって、図1の点線に示す従来例では、脱炭吹錬中期までは、脱燐反応よりも持ち越しスラグを含んだ脱炭スラグからの復燐の方が大きく、溶鉄中のP濃度はわずかに上昇する傾向にある。 FIG. 1 is a diagram for explaining transition of P concentration in molten iron during decarburization blowing. Part of the dephosphorization slag produced by dephosphorization blowing inevitably remains as carryover slag. In order to separate the dephosphorization slag and the hot metal as much as possible as described above, the decarburization slag contains carryover slag, but the amount of SiO2 decreases, and decarburization progresses due to excessive addition of the lime source. up to, the liquid phase ratio of the decarburized slag decreases, and the dephosphorization rate becomes excessively slow. Therefore, in the conventional example indicated by the dotted line in FIG. tend to rise.
そこで本実施形態では、脱炭吹錬中の石灰源の全投入量を全CaO換算質量で30~70kg/t-steelの範囲とし、脱炭スラグの液相率を確保するために、脱炭吹錬を開始する時点で、石灰源を全CaO換算質量の60~80%だけ投入する。 Therefore, in this embodiment, the total amount of lime source input during decarburization blowing is set in the range of 30 to 70 kg / t-steel in terms of total CaO mass, and in order to ensure the liquid phase ratio of decarburization slag, decarburization At the time of starting blowing, the lime source is charged in an amount of 60 to 80% of the total CaO equivalent mass.
ここで、上述の石灰源の全投入量は低燐鋼向け脱炭吹錬で一般的に投入される石灰源の量である。石灰源の全投入量が全CaO換算質量で30kg/t-steel未満では、目的とする低燐鋼を溶製することができない。また、石灰源の全投入量が全CaO換算質量で70kg/t-steel超では、脱燐効果が飽和し、スラグ量が増加するとともに石灰源のコストが多くかかってしまう。また、脱炭吹錬を開始する時点で投入する石灰源が全CaO換算質量の60%未満では、脱炭スラグのCaO分が少なくなり、かつ後入れした石灰源の溶解が間に合わず最終的な脱燐量が少なくなってしまう。また、脱炭吹錬を開始する時点で投入する石灰源が全CaO換算質量の80%超では、脱炭吹錬前半の脱炭スラグの液相率が低下し、特に脱炭吹錬中期での脱燐量が低下してしまう。 Here, the total input amount of lime source mentioned above is the amount of lime source generally input in decarburization blowing for low-phosphorus steel. If the total amount of lime source input is less than 30 kg/t-steel in terms of total CaO mass, the desired low-phosphorus steel cannot be melted. Further, if the total amount of lime source input exceeds 70 kg/t-steel in terms of total CaO mass, the dephosphorization effect becomes saturated, the amount of slag increases, and the cost of lime source increases. In addition, if the lime source to be added at the time of starting decarburization blowing is less than 60% of the total CaO equivalent mass, the CaO content of the decarburized slag will be small, and the lime source that has been added will not be dissolved in time and the final The amount of dephosphorization decreases. In addition, when the lime source to be introduced at the time of starting decarburization blowing exceeds 80% of the total CaO equivalent mass, the liquid phase ratio of decarburization slag in the first half of decarburization blowing decreases, especially in the middle period of decarburization blowing. The amount of dephosphorization of will decrease.
図2は、脱炭吹錬中の脱炭スラグの液相率の推移を説明するための図である。本実施形態においては、脱炭吹錬を開始する時点で、石灰源を全CaO換算質量の60~80%だけ投入することにより脱炭スラグの液相率を確保し、特に脱炭吹錬中期までの脱燐反応効率を上げるようにしている。これにより図1に示すように、従来に比べて、特に脱炭吹錬中期での溶鉄中のP濃度を低く抑えることができる。 FIG. 2 is a diagram for explaining the transition of the liquid fraction of decarburized slag during decarburization blowing. In this embodiment, at the time of starting decarburization blowing, the lime source is added by 60 to 80% of the total CaO equivalent mass to ensure the liquid phase ratio of decarburization slag, especially in the middle of decarburization blowing He is trying to raise the dephosphorization reaction efficiency up to. As a result, as shown in FIG. 1, the concentration of P in the molten iron can be kept lower than in the conventional case, particularly in the middle stage of decarburization blowing.
以上のように脱炭吹錬を開始する時点で石灰源の一部を残し、送酸速度が150~250Nm3/(h・t-steel)の範囲で脱炭吹錬を開始する。そして、吹錬開始時点から総酸素量中の流量割合で80~90%を供給した時点において残りの石灰源を投入し、かつ送酸速度を下記(1)式の範囲に変更する。
0.40≦FO2_after/FO2_before≦0.85 ・・・(1)
As described above, when decarburization blowing is started, part of the lime source is left and decarburization blowing is started at an oxygen feeding rate in the range of 150 to 250 Nm 3 /(h·t-steel). Then, when 80 to 90% of the total oxygen flow rate is supplied from the start of blowing, the remaining lime source is added, and the oxygen supply rate is changed to the range of the following formula (1).
0.40≦F 02_after /F 02_before ≦0.85 (1)
ここで、FO2_beforeは、送酸速度を変更する前の送酸速度(Nm3/(h・t-steel))を表し、FO2_afterは、残りの石灰源を投入した段階で送酸速度を変更した後の送酸速度(Nm3/(h・t-steel))である。 Here, FO2_before represents the acid feed rate (Nm 3 /(h·t-steel)) before changing the acid feed rate, and FO2_after is the acid feed rate at the stage when the remaining lime source is added. This is the acid feed rate (Nm 3 /(h·t-steel)) after the change.
ここで、上述の吹錬開始時における150~250Nm3/(h・t-steel)の送酸速度の範囲は、脱炭吹錬で一般的に吹き込まれる酸素の送酸速度である。この時の送酸速度が150Nm3/(h・t-steel)未満では、脱炭が十分に行われず、無駄に多くの時間がかかってしまう。また、送酸速度が250Nm3/(h・t-steel)超に増加させることは、設備仕様上困難であったり、溶鉄飛散や耐火物損耗など操業上の問題が生じる場合があったりする。 Here, the range of the oxygen supply rate of 150 to 250 Nm 3 /(h·t-steel) at the start of blowing is the oxygen supply rate of oxygen generally blown in decarburization blowing. If the oxygen supply rate at this time is less than 150 Nm 3 /(h·t-steel), decarburization will not be sufficiently carried out, and a lot of time will be wasted. Also, increasing the oxygen supply rate to over 250 Nm 3 /(h·t-steel) may be difficult in terms of facility specifications, and may cause operational problems such as molten iron scattering and refractory wear.
また、上述の条件で脱炭吹錬を行った場合に、総酸素量の流量割合で80~90%を供給すると、溶鉄中のCが概ね除去され、FeOが生成しやすくなる。FeOが生成されると図2に示したように脱炭スラグの液相率が上昇し、脱燐反応が起こりやすくなる。吹錬開始時点から総酸素量中の流量割合で80%未満の段階で残りの石灰源を投入して送酸速度を(1)式の範囲に変更すると、追加で投入した石灰源により脱炭スラグの液相率が過度に低下してしまい、脱燐効率が低下する。さらに、脱炭反応がまだ顕著に生じている段階(FeOがまだあまり生成されない段階)で送酸を抑えることになるため、Feの過剰酸化が生じ、鉄の歩留まりが低下してしまう。また、吹錬開始時点から総酸素量中の流量割合で90%超の段階で残りの石灰源を投入して送酸速度を(1)式の範囲に変更すると、脱炭スラグ中においてFeOの割合が高い脱炭吹錬末期での時間を十分に確保できず、追加で投入した石灰源の滓化が不十分となり、脱燐効果が十分に得られない。 Further, when decarburization blowing is performed under the above conditions, if 80 to 90% of the total oxygen flow rate is supplied, C in the molten iron is generally removed, and FeO is easily generated. When FeO is generated, the liquid phase ratio of the decarburized slag increases as shown in FIG. 2, making the dephosphorization reaction more likely to occur. When the remaining lime source is added at a stage where the flow rate ratio in the total oxygen amount is less than 80% from the start of blowing and the oxygen supply rate is changed to the range of formula (1), the additionally added lime source decarburizes The liquid phase ratio of the slag is excessively lowered, and the dephosphorization efficiency is lowered. Furthermore, since the oxygen supply is suppressed at the stage where the decarburization reaction is still occurring significantly (the stage where FeO is not yet generated much), excessive oxidation of Fe occurs and the yield of iron decreases. In addition, when the remaining lime source is added at the stage where the flow rate ratio in the total oxygen amount exceeds 90% from the start of blowing and the oxygen supply rate is changed to the range of formula (1), FeO is added to the decarburized slag. Sufficient time cannot be secured in the final stage of decarburization blowing, which has a high ratio, and the slag of the additionally supplied lime source becomes insufficient, so that a sufficient dephosphorization effect cannot be obtained.
図3は、送酸速度の変更による脱炭吹錬末期の時間の延長を説明するための図である。図3において、II期とは、脱炭反応が顕著に進行している脱炭吹錬中期を表し、III期は、脱炭反応が低下してFeOの生成が増加する脱炭吹錬末期を表している。例えば、脱炭吹錬中期まで送酸速度を60000Nm3/hとし、追加で石灰源を投入した時に送酸速度を下げると、総酸素量を同じにした場合に脱炭吹錬末期の時間を延ばすことができる。 FIG. 3 is a diagram for explaining the extension of time in the final stage of decarburization blowing by changing the oxygen supply rate. In FIG. 3, period II represents the middle stage of decarburization blowing in which the decarburization reaction is progressing remarkably, and period III represents the final stage of decarburization blowing in which the decarburization reaction decreases and the production of FeO increases. represents. For example, if the oxygen supply rate is set to 60000 Nm 3 /h until the middle stage of decarburization blowing and the oxygen supply rate is lowered when an additional lime source is added, the time at the end of decarburization blowing is reduced when the total amount of oxygen is the same. can be extended.
また、図4に示すように、送酸速度を下げると、送酸速度を下げなかった場合に比べて脱炭スラグ中のFeO濃度は小さくなるが、脱炭吹錬末期の脱燐反応は酸素供給律速ではなく、溶鉄中と脱炭スラグ中とのPの物質移動律速となる。したがって、送酸速度を低下させたとしても単位時間あたりの脱燐量は殆ど変わらないため、総酸素量が同じであれば送酸速度を下げて時間を延ばすほど溶鉄中のP濃度が低下する。よって、総酸素量の増加による過度なFeの酸化(鉄歩留まりの低下)や大幅な時間延長を回避して脱燐効率を改善できる。 In addition, as shown in FIG. 4, when the oxygen supply rate is lowered, the FeO concentration in the decarburization slag becomes lower than when the oxygen supply rate is not lowered. It is not supply rate-limiting, but mass transfer rate-limiting of P between molten iron and decarburized slag. Therefore, even if the oxygen supply rate is lowered, the amount of dephosphorization per unit time is almost unchanged. Therefore, if the total oxygen content is the same, the P concentration in the molten iron decreases as the oxygen supply rate is lowered and the time is extended. . Therefore, it is possible to avoid excessive oxidation of Fe (reduced yield of iron) due to an increase in the total amount of oxygen and a significant extension of time, thereby improving dephosphorization efficiency.
図5は、脱炭吹錬前後での脱燐率と比FO2_after/FO2_beforeとの関係を示す図である。図5に示すように、(1)式を満たすように送酸速度を調整することによって脱燐率が75%以上となることがわかる。比FO2_after/FO2_beforeを0.85超に調整すると、脱燐反応が起こりやすい脱炭吹錬末期の時間確保が不十分となり脱燐効果が得られない。一方、比FO2_after/FO2_beforeを0.40未満に調整すると、脱燐反応の駆動力であるP濃度の実績値と平衡値との差が小さくなり、脱炭吹錬末期の時間を延ばしたことによる脱燐効果が飽和する。また、上吹き酸素ジェットが過度にソフトブローとなり、FeO生成速度に対する底吹き攪拌による脱炭スラグ中のFeO還元反応速度が大きくなり、脱炭スラグ中のFeO濃度の増加が鈍化してしまうため、脱燐効率が寧ろ低下してしまう。 FIG. 5 is a diagram showing the relationship between the dephosphorization rate and the ratio FO2_after / FO2_before before and after decarburization blowing. As shown in FIG. 5, it can be seen that the dephosphorization rate is 75% or more by adjusting the oxygen feeding rate so as to satisfy the formula (1). If the ratio F 02_after /F 02_before is adjusted to more than 0.85, the dephosphorization effect cannot be obtained because the final stage of decarburization blowing, in which the dephosphorization reaction tends to occur, cannot be ensured sufficiently. On the other hand, when the ratio F 02_after /F 02_before was adjusted to less than 0.40, the difference between the actual value of the P concentration, which is the driving force for the dephosphorization reaction, and the equilibrium value decreased, and the time at the end of the decarburization blowing was extended. Therefore, the dephosphorization effect is saturated. In addition, the top-blown oxygen jet becomes an excessively soft blow, and the FeO reduction reaction rate in the decarburized slag due to the bottom-blown stirring relative to the FeO generation rate increases, and the increase in the FeO concentration in the decarburized slag slows down. The dephosphorization efficiency rather decreases.
また、追加で石灰源を投入する前または後の段階においても送酸速度を適宜変更してもよい。図6は、送酸速度と送酸量原単位との関係を示す図である。追加で石灰源を投入する段階で送酸速度を変更する前に送酸速度を変更した場合は、その期間に供給した酸素量を吹錬時間で除した平均の送酸速度をFO2_beforeとする。追加で石灰源を投入する段階で送酸速度を変更した後に送酸速度を変更した場合も同様に、平均の送酸速度をFO2_afterとする。 Also, before or after adding the lime source, the oxygen supply rate may be changed as appropriate. FIG. 6 is a diagram showing the relationship between the oxygen transfer rate and the basic unit of the oxygen transfer amount. If the oxygen supply rate is changed before changing the oxygen supply rate at the stage of adding the lime source, the average oxygen supply rate obtained by dividing the amount of oxygen supplied during that period by the blowing time is set to FO2_before . . Similarly, when the acid feeding rate is changed after changing the acid feeding rate at the stage of adding the lime source, the average acid feeding rate is set to F O2_after .
また、本実施形態における脱炭吹錬では、溶鉄中C濃度を0.4質量%未満にまで低減するものとする。C濃度が0.4質量%以上の高炭素鋼を溶製する場合には、FeOが生成されにくい段階で酸素の吹込みを止める必要があるからである。さらに、攪拌条件については特に限定しないが、底吹きガスの種類、羽口形状に応じて一般的な脱炭吹錬の条件で行うものとする。 Moreover, in decarburization blowing in this embodiment, C concentration in molten iron shall be reduced to less than 0.4 mass %. This is because, when melting high-carbon steel having a C concentration of 0.4% by mass or more, it is necessary to stop blowing oxygen at a stage where FeO is difficult to generate. Furthermore, the stirring conditions are not particularly limited, but the general decarburization blowing conditions are used according to the type of bottom-blown gas and the shape of the tuyeres.
以上のように、脱炭吹錬開始時において石灰源を全CaO換算質量の60~80%だけ投入し、吹錬開始時点から総酸素量中の流量割合で80~90%を供給した時点において残りの石灰源を投入し、かつ送酸速度を(1)式の範囲に変更することにより、脱炭吹錬中期までにおいても脱燐反応を促進させ、かつ脱燐反応が起こりやすい脱炭吹錬末期を延ばし、鉄歩留まりを低下させずに脱燐効率を高めることができる。 As described above, at the start of decarburization blowing, 60 to 80% of the total CaO equivalent mass of the lime source is added, and from the start of blowing, at the time of supplying 80 to 90% of the total oxygen flow rate. By adding the remaining lime source and changing the oxygen supply rate to the range of formula (1), the dephosphorization reaction is promoted even in the middle stage of decarburization blowing, and the decarburization blowing reaction is likely to occur. It is possible to extend the final stage of smelting and improve the dephosphorization efficiency without lowering the iron yield.
次に、本発明の実施例について説明するが、この条件は、本発明の実施可能性及び効果を確認するための一条件例であり、本発明は、この実施例の記載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種々の手段にて実施することができる。 Next, an example of the present invention will be described, but this condition is an example of conditions for confirming the feasibility and effect of the present invention, and the present invention is limited to the description of this example. is not. The present invention can be implemented in various ways to achieve the objects of the present invention without departing from the gist of the present invention.
高炉から出銑した後の溶銑を転炉に装入し、脱燐吹錬を実施して溶銑中のP濃度が0.040質量%以下になるまでPを除去した。その後、溶銑の出湯および脱燐スラグの排滓により溶銑と脱燐スラグとを分離し、320tの予備処理済の溶銑を得た。その後、処理済みの溶銑を転炉に戻し、昇熱材としての炭材、FeSi、および石灰源(CaO)を投入して溶銑の脱炭吹錬を実施し、C濃度を0.03質量%以上0.4質量%未満まで低減させた。この時の脱炭吹錬前の溶銑中P濃度は0.02~0.04質量%の範囲、脱炭吹錬で新規に投入した石灰源の全投入量は全CaO換算質量で溶銑1tあたり50~60kg、送酸速度変更前の平均の送酸速度FO2_beforeは191~213Nm3/(h・t-steel)とした。 Hot metal tapped from a blast furnace was charged into a converter, and dephosphorization blowing was performed to remove P until the P concentration in the hot metal became 0.040% by mass or less. Thereafter, hot metal was tapped and dephosphorization slag was discharged to separate the hot metal and dephosphorization slag to obtain 320 tons of pretreated hot metal. After that, the treated hot metal is returned to the converter, and the carbonaceous material, FeSi, and lime source (CaO) as heating materials are added to decarburize the hot metal, and the C concentration is reduced to 0.03% by mass. It was reduced to less than 0.4% by mass. At this time, the P concentration in the hot metal before decarburization blowing is in the range of 0.02 to 0.04% by mass, and the total amount of lime source newly added in the decarburization blowing is the total CaO equivalent mass per 1 ton of hot metal. 50 to 60 kg, and the average oxygen supply rate F O2_before was set to 191 to 213 Nm 3 /(h·t-steel).
本発明の効果は、溶銑の脱燐率、スラグ中のFeO濃度で評価した。脱炭吹錬前後に採取したメタルサンプルの化学分析で得たP濃度から以下の(2)式で脱燐率を算出し、脱炭吹錬後のスラグ化学分析からFeO濃度を分析した。本実施例では、脱燐率が75%以上、FeO濃度が30質量%未満をともに満たした条件で発明の効果が得られたと判断した。
脱燐率=100*([P]脱C前-[P]脱C後)/[P]脱C前 ・・・(2)
なお、[P]脱C前は脱炭吹錬前の溶銑中P濃度を表し、[P]脱C後は脱炭吹錬後の溶鋼中P濃度を表す。
The effect of the present invention was evaluated by the dephosphorization rate of hot metal and the FeO concentration in slag. The dephosphorization rate was calculated by the following formula (2) from the P concentration obtained by chemical analysis of the metal samples collected before and after decarburization blowing, and the FeO concentration was analyzed by slag chemical analysis after decarburization blowing. In this example, it was determined that the effects of the invention were obtained under the conditions that both the dephosphorization rate was 75% or more and the FeO concentration was less than 30% by mass.
Dephosphorization rate = 100 * ([P] before deC - [P] after deC) / [P] before deC (2)
In addition, [P] before decarburization represents the P concentration in molten iron before decarburization blowing, and [P] after decarburization represents the P concentration in molten steel after decarburization blowing.
表1に示すように、実施例No.1~No.4においては、いずれも脱燐率が75%以上で、かつ脱炭スラグ中のFeO濃度が30質量%未満であった。 As shown in Table 1, Example No. 1 to No. In No. 4, the dephosphorization rate was 75% or more, and the FeO concentration in the decarburized slag was less than 30% by mass.
一方で、比較例No.5は、石灰源を分割投入せず、送酸速度も変更しなかったため、脱炭吹錬中期までの脱炭スラグの液相率が低く、さらに脱燐反応が進行しやすい脱炭吹錬末期も延ばすことができなかった。その結果、脱燐率が低かった。比較例No.6では、脱炭吹錬開始時点での石灰源の投入量が少なかったため、脱炭吹錬末期に投入した石灰源が多くなり、その結果、追加で投入した石灰源が完全に溶解せず脱燐率が低かった。比較例No.7では、脱炭吹錬開始時点での石灰源の投入量が多すぎたため、脱炭吹錬中期までの脱炭スラグの液相率が低かった。その結果、脱燐率が低かった。 On the other hand, Comparative Example No. In 5, since the lime source was not divided and the oxygen supply rate was not changed, the liquid phase ratio of the decarburization slag was low until the middle stage of the decarburization blowing, and the dephosphorization reaction easily progressed at the end of the decarburization blowing. could not be extended. As a result, the dephosphorization rate was low. Comparative example no. In 6, the amount of lime source input at the start of decarburization blowing was small, so the lime source input at the end of decarburization blowing increased, and as a result, the additionally input lime source was not completely dissolved and degassed. Phosphorus rate was low. Comparative example no. In No. 7, the amount of lime source input at the start of decarburization blowing was too large, so the liquid phase ratio of decarburization slag was low until the middle stage of decarburization blowing. As a result, the dephosphorization rate was low.
比較例No.8では、残りの石灰源の投入および送酸速度の変更が早すぎたため、脱炭吹錬中期での脱炭スラグの液相率が低くなり、脱燐率が低かった。さらに、Feの過剰酸化が生じたことから、脱炭スラグ中のFeO濃度も高かった。比較例No.9では、残りの石灰源の投入および送酸速度の変更が遅すぎたため、脱炭吹錬末期での時間を十分に確保できず、追加で投入した石灰源の滓化が不十分となり、脱燐率が低かった。 Comparative example no. In No. 8, since the remaining lime source was added and the oxygen supply rate was changed too quickly, the decarburization slag liquid phase ratio was low in the middle stage of decarburization blowing, and the dephosphorization rate was low. Furthermore, the FeO concentration in the decarburized slag was also high due to excessive oxidation of Fe. Comparative example no. In 9, since the remaining lime source was added and the oxygen transfer rate was changed too slowly, sufficient time could not be secured at the end of decarburization blowing, and the additionally added lime source was insufficiently turned into slag. Phosphorus rate was low.
比較例No.10では、残りの石灰源の投入時に送酸速度を下げ過ぎたため、脱炭スラグ中のFeO濃度の増加が鈍化して脱炭スラグの液相率の上昇が緩やかになり過ぎ、脱燐率が低かった。比較例No.11では、残りの石灰源の投入時の送酸速度の下げ幅が小さ過ぎたため、脱炭吹錬末期の時間の延長効果があまり得られず、脱燐率が低かった。 Comparative example no. In No. 10, since the oxygen supply rate was too low when the remaining lime source was added, the increase in the FeO concentration in the decarburization slag slowed down, the increase in the liquid fraction of the decarburization slag became too slow, and the dephosphorization rate decreased. was low. Comparative example no. In No. 11, the decrease in the oxygen supply rate at the time of charging the remaining lime source was too small, so the effect of extending the time at the end of decarburization blowing was not so much obtained, and the dephosphorization rate was low.
Claims (1)
前記脱炭吹錬において、吹錬を開始する時点で前記石灰源を前記全CaO換算質量の60~80%投入し、前記上吹きランスから送酸速度が150~250Nm3/(h・t-steel)の範囲で酸素を吹き付けて吹錬を開始し、吹錬開始時点から総酸素量中の流量割合で80~90%の酸素を供給した時点において、前記石灰源の残りを投入するとともに送酸速度を(1)式の範囲に変更することを特徴とする、低燐鋼の溶製方法。
0.40≦FO2_after/FO2_before≦0.85 ・・・(1)
ここで、FO2_before:前記石灰源の残りを投入するとともに送酸速度を変更する前の送酸速度(Nm3/(h・t-steel))、FO2_after:前記石灰源の残りを投入するとともに送酸速度を変更した後の送酸速度(Nm3/(h・t-steel))である。 After separating the dephosphorization slag produced by dephosphorization blowing in a converter type refining apparatus equipped with a top blowing lance, a lime source containing CaO or CaCO 3 is added at a total CaO equivalent mass of 30 to 70 kg / t. - A low-phosphorus steel smelting method in which decarburization blowing is performed by charging in the steel range and the C concentration in the molten iron is reduced to less than 0.4% by mass,
In the decarburization blowing, 60 to 80% of the total CaO-equivalent mass of the lime source is introduced at the start of blowing, and the oxygen feed rate is 150 to 250 Nm 3 /(ht- Steel) is blown to start blowing, and when oxygen is supplied at a rate of 80 to 90% of the total oxygen amount from the start of blowing, the rest of the lime source is added and fed. A method for melting low-phosphorus steel, characterized by changing the acid rate to the range of formula (1).
0.40≦F 02_after /F 02_before ≦0.85 (1)
Here, F O2_before : the acid supply rate (Nm 3 /(h·t-steel)) before the rest of the lime source is added and the acid supply rate is changed, F O2_after : the rest of the lime source is added and the acid feed rate (Nm 3 /(h·t-steel)) after changing the acid feed rate.
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