JP5332769B2 - How to use electric furnace slag - Google Patents
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- JP5332769B2 JP5332769B2 JP2009064610A JP2009064610A JP5332769B2 JP 5332769 B2 JP5332769 B2 JP 5332769B2 JP 2009064610 A JP2009064610 A JP 2009064610A JP 2009064610 A JP2009064610 A JP 2009064610A JP 5332769 B2 JP5332769 B2 JP 5332769B2
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Description
本発明は、電気炉酸化精錬にて発生するスラグを有効活用する方法に関するものである。 The present invention relates to a method for effectively utilizing slag generated in electric furnace oxidation refining.
製鋼プロセスから排出されるスラグは一部で路盤材適用などの資源化が進められてはいるが，その使用範囲は、土壌環境基準などの制限があり、必ずしも十分ではなく，環境問題の観点からも発生スラグ量は極力削減することが望まれている。 Although some of the slag discharged from the steelmaking process has been promoted as resources, such as the application of roadbed materials, the range of use is not always sufficient due to restrictions such as soil environmental standards. In addition, it is desired to reduce the amount of generated slag as much as possible.
スラグ発生量の低減策としてはスラグのリサイクル使用があり，例えば特許文献１には転炉スラグにボーキサイト，鉄鉱石，マンガン鉱石などを加えて，塩基度，Ａｌ2Ｏ3濃度，Ｔ．Ｆｅ濃度及びＭｎＯ濃度を制御したうえで脱燐用フラックスとして用いる転炉スラグのリサイクル方法が提案されており，特許文献２では転炉スラグを高炉原料または焼結原料として用いる方法が開示されている。さらに，特許文献３においては脱燐スラグのリサイクル方法として，前回チャージにて使用したスラグの一部を容器内に残留させて，再度，スラグ生成量を減少させる方法が提案されている。
As a measure for reducing the amount of generated slag, there is a recycling use of slag. For example, in
しかしながら，特許文献１における方法はボーキサイト，鉄鉱石，マンガン鉱石等を配合させるという別途の工程が必要となることに加え，これらの原料自体のコストがかかるなどの問題があり，特許文献２の方法ではリサイクル量に制限があり転炉スラグを全量リサイクルすることが困難であるなどの問題があった。さらに，特許文献３の方法ではリサイクルされるスラグ自体が溶銑脱燐スラグであるため処理温度が低く，リサイクル処理を行っても十分なスラグ滓化が達成されず，脱燐効率が不安定であるなどの問題があった。
However, the method in
電気炉で発生するスラグについても、十分に利用できる技術が確立されていなかった。 For slag generated in electric furnaces, a technology that can be fully utilized has not been established.
本発明はかかる事情を鑑みてなされたもので，電気炉スラグを製鋼プロセスの中で利用可能とする方法を提供することを目的とするものである。 The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for making an electric furnace slag usable in a steelmaking process.
本発明者らは，種々の実験・調査を行うことにより、電気炉酸化精錬にて生成滓化したスラグを脱燐などの転炉吹錬にて利用することで転炉での脱燐効率を向上させること、及び脱燐処理に要する生石灰などのフラックス原単位を減少させることが可能であることを知見した。 By conducting various experiments and investigations, the present inventors have used the slag produced and hatched by electric furnace oxidation refining in converter blowing such as dephosphorization to improve the dephosphorization efficiency in the converter. It has been found that it is possible to improve and reduce the basic unit of flux such as quicklime required for the dephosphorization treatment.
本発明は、上記の知見に基づきなされたものであり，その要旨は以下に示す通りである。
（１）転炉で溶銑の脱珪脱燐処理を行うに際し，造滓材の一部として、電気炉で鉄スクラップの溶解及び脱燐を含む酸化精錬により発生した、Ｔ．Ｆｅ：１５〜２５質量％を含む電気炉スラグを転炉に装入して利用する方法であって、転炉に装入する電気炉スラグ量を、前記溶銑の脱珪脱燐処理により発生するスラグ量に対する比率が５質量％以上３０質量％未満となるように装入することを特徴とする電気炉スラグの利用方法。
（２）電気炉スラグを、脱珪脱燐処理の開始から終了までの時間中の該開始後の７０％以後から９０％以前の間において転炉に装入することを特徴とする上記（１）記載の電気炉スラグの利用方法。
The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) When carrying out desiliconization and dephosphorization of hot metal in a converter, as a part of the ironmaking material, T. was generated by oxidation refining including melting and dephosphorization of iron scrap in an electric furnace. Fe: A method of using electric furnace slag containing 15 to 25% by mass in a converter, and generating the amount of electric furnace slag charged in the converter by desiliconization and dephosphorization of the hot metal. A method of using electric furnace slag, wherein the charging is performed so that the ratio to the slag amount is 5% by mass or more and less than 30% by mass .
(2) The above-mentioned (1 ), wherein the electric furnace slag is charged into the converter between 70% and 90% after the start of the desiliconization and dephosphorization process. ) How to use electric furnace slag as described.
本発明によれば，電気炉スラグを転炉精錬に利用することにより、転炉において、少量の生石灰原単位により効率的な脱硅脱燐精錬を可能とすることが出来る。 According to the present invention, by using electric furnace slag for converter refining, efficient desulfurization and dephosphorization can be performed in a converter with a small amount of quicklime basic unit.
以下に本発明について詳細に説明する。 The present invention is described in detail below.
溶銑の脱珪脱燐処理は、溶銑を転炉に装入する前の高炉鋳床での脱珪処理やトーピードカー内での脱珪脱燐処理の他、近年では、前掲の特許文献３で開示されているように、転炉内で脱珪脱燐処理が行われるようになって来ている。 The desiliconization and dephosphorization treatment of hot metal is disclosed in the above-mentioned Patent Document 3 in addition to the desiliconization treatment in the blast furnace cast floor before charging the hot metal into the converter and the desiliconization and dephosphorization treatment in the torpedo car. As described above, desiliconization and phosphorous removal treatment is performed in a converter.
本発明は、転炉内での溶銑の脱珪脱燐処理を対象とするものであり、通常、脱炭処理時より弱い酸素吹錬を行うと共に、造滓材が添加される。 The present invention is intended for desiliconization and dephosphorization of hot metal in a converter. Usually, oxygen blowing is performed weaker than that during decarburization, and a slagging material is added.
本発明において、脱珪脱燐処理の開始とは、転炉に溶銑を装入した後、脱珪脱燐処理のための上記の酸素吹錬を開始したときを言い、該処理の終了とは、前記酸素吹錬を終了したときを言う。 In the present invention, the start of desiliconization and dephosphorization refers to the time when the above-mentioned oxygen blowing for desiliconization and dephosphorization is started after hot metal is charged into the converter, and the end of the treatment is The time when the oxygen blowing is finished.
電気炉においては、通常、スクラップ溶解及び脱燐などの酸化精錬を行って溶鋼を出鋼し，その後、専用の受け皿（スラグパン）上にスラグの排出を行う（出滓処理）。 In an electric furnace, usually, smelting and dephosphorization are performed to remove molten steel, and then the slag is discharged on a dedicated tray (slag pan) (slagging process).
本発明の転炉精錬で利用する電気炉スラグは、スラグパンに排出されたスラグを冷却後，破砕機にて転炉装入が可能な適度な寸法に破砕し，及び地金除去を行い，その後スラグに付着した水分除去を目的とした乾燥処理を実施する。なおここで破砕するスラグの適度な寸法としては，１ｍｍ径以上５０ｍｍ径未満であることが好ましい。これは，１ｍｍ径以下の微細粒では転炉炉上から添加を行う際に飛散分が増えることなどによって電気炉スラグの添加歩留の低下が顕著となってしまうためであり，逆に５０ｍｍ径を超える粗粒では炉内添加後に電気炉スラグ自体の溶解に長時間を要し，滓化材としての機能が十分に発揮されないためである。 The electric furnace slag used in the converter refining of the present invention is to cool the slag discharged to the slag pan, crush it to an appropriate size that can be charged in the converter with a crusher, and remove the metal. A drying process is performed to remove water adhering to the slag. In addition, as an appropriate dimension of the slag crushed here, it is preferable that it is 1 mm diameter or more and less than 50 mm diameter. This is because, in the case of fine particles having a diameter of 1 mm or less, a decrease in the addition yield of the electric furnace slag becomes conspicuous due to an increase in scattering when the addition is performed from the top of the converter furnace. This is because, if the coarse grains exceed 50%, it takes a long time to dissolve the electric furnace slag itself after the addition in the furnace, and the function as the hatching material is not fully exhibited.
本発明では、破砕，乾燥した電気炉スラグを転炉炉上に搬送し，該転炉内に溶銑を装入した後、生石灰等の造滓材を添加し塩基度などの成分調整を行うことで脱硅脱燐処理の吹酸精錬を行うに際し，炉上に搬送した電気炉スラグを造滓材として、上記生石灰等の造滓材に加えて転炉に装入する。 In the present invention, the crushed and dried electric furnace slag is transported onto the converter furnace, and hot metal is charged into the converter, and then a component such as quick lime is added to adjust components such as basicity. When performing blown acid refining in the dephosphorization and dephosphorization process, the electric furnace slag transported on the furnace is used as a steel making material in addition to the steel making material such as quick lime and charged into the converter.
この際，転炉に装入する電気炉スラグ量を，転炉での脱珪脱燐処理にて発生するスラグ量の５％以上３０％未満とすることにより、脱硅脱燐処理において極めて効率的な脱燐処理を行うことが可能となる。ここで，脱珪脱燐処理にて発生するスラグ量は、溶銑［Ｓｉ］濃度及び設定塩基度により以下の手法にて計算することが可能である。まず，溶銑中の［Ｓｉ］濃度によりスラグとして生成するＳｉＯ2量が必然的に決定し，該脱珪脱燐処理に適切な塩基度（ＣａＯ／ＳｉＯ2）設定値よりＣａＯ量が決定される。スラグ全体に占めるＣａＯ，ＳｉＯ2の比率は経験的に約７５％となるこことが一般的に知られており，これにより該脱珪脱燐処理により発生する全スラグ量が、ほぼ予測できるが、事前の操業試験により、溶銑［Ｓｉ］濃度、目標とする塩基度とするための生石灰等の造滓材量、および本発明で装入する電気炉スラグ量と、実際に発生した全スラグ量との関係を調査して、全スラグ量を予測する式を求めておくことにより、より精度の高い予測が可能である。実際の全スラグ量は、脱珪脱燐処理後にスラグを転炉からスラグパンに排出して秤量することにより把握できる。 At this time, the amount of electric furnace slag charged in the converter is set to 5% or more and less than 30% of the amount of slag generated in the desiliconization and dephosphorization process in the converter, so that the degassing and dephosphorization process is extremely efficient. It is possible to perform a dephosphorization process. Here, the amount of slag generated in the desiliconization and dephosphorization treatment can be calculated by the following method depending on the hot metal [Si] concentration and the set basicity. First, the amount of SiO 2 produced as slag is inevitably determined by the [Si] concentration in the hot metal, and the amount of CaO is determined from the basicity (CaO / SiO 2 ) setting value appropriate for the desiliconization and dephosphorization treatment. . It is generally known that the ratio of CaO and SiO 2 occupying the entire slag is empirically about 75%, so that the total amount of slag generated by the desiliconization and dephosphorization treatment can be almost predicted. The amount of molten iron [Si], the amount of slagging material such as quick lime to achieve the target basicity, the amount of electric furnace slag to be charged in the present invention, and the total amount of slag actually generated by a prior operation test And a formula for predicting the total slag amount is obtained, so that a more accurate prediction is possible. The actual total slag amount can be grasped by discharging the slag from the converter to the slag pan and weighing it after the desiliconization and dephosphorization treatment.
溶銑脱燐処理における脱燐効率はスラグの滓化性に大きく依存する。電気炉精錬により発生するスラグの主組成は，溶製する鋼種やスクラップ等の原料及び操業条件などにより異なる場合があるが，普通鋼溶製の場合ではスクラップ溶解のための通電や高炉溶銑を併用した際の脱燐負荷などの観点から，（％ＣａＯ）＝４０〜４５質量％，（％ＳｉＯ2）＝１５〜２０質量％，（％Ｔ．Ｆｅ）＝１５〜２５質量％，（％Ａｌ2Ｏ3）＝３〜６質量％，（％ＭｎＯ）＝４〜８質量％，（％Ｐ2Ｏ5）＝１〜２質量％，（％ＭｇＯ）＝３〜８質量％，（％Ｃｒ2Ｏ3）≦３質量％などの範囲であることが多いが転炉精錬に比べ在炉時間が長く，かつ最終的には１６００℃〜１７００℃の高温処理となるため極めて滓化性が良く，遊離石灰分（ｆ．ＣａＯ）が２質量％以下のスラグとなる。 The dephosphorization efficiency in the hot metal dephosphorization treatment depends greatly on the hatchability of the slag. The main composition of slag generated by electric furnace refining may vary depending on the type of steel to be smelted, raw materials such as scrap, and operating conditions, etc. (% CaO) = 40 to 45 mass%, (% SiO 2 ) = 15 to 20 mass%, (% T.Fe) = 15 to 25 mass%, (% Al 2 O 3 ) = 3-6 mass%, (% MnO) = 4-8 mass%, (% P 2 O 5 ) = 1-2 mass%, (% MgO) = 3-8 mass%, (% Cr 2 O 3 ) ≤ 3% by mass, etc., but the in-furnace time is longer than that in converter refining, and the final high temperature treatment at 1600 ° C to 1700 ° C results in very good hatchability. , Slag having a free lime content (f.CaO) of 2% by mass or less.
本発明者らはこの滓化性の良い電気炉スラグを転炉での脱硅脱燐処理時の造滓材として活用することで，別に添加するＣａＯの滓化性も向上し，かつＣａＯ原単位を低減させるとともに効率的な脱燐処理を行うことが可能であることを見出した。 The inventors of the present invention have improved the hatchability of CaO added separately by using this electric furnace slag with good hatchability as a steelmaking material at the time of dephosphorization and dephosphorization treatment in the converter, and the CaO raw material. It has been found that it is possible to reduce the unit and perform an efficient dephosphorization treatment.
すなわち，電気炉精錬により発生したスラグを転炉での脱硅脱燐吹錬に利用することで，脱燐造滓材として使用するＣａＯの一部を置換代替することでＣａＯ原単位の削減を可能とするとともに，滓化性の良好な電気炉スラグを滓化促進材としての活用が可能となる。 In other words, slag generated by electric furnace refining is used for dephosphorization and dephosphorization blowing in converters, so that a part of CaO used as a dephosphorizing material can be replaced and replaced to reduce the basic unit of CaO. This makes it possible to use an electric furnace slag with good hatchability as a hatching accelerator.
図１は、一例として，（％ＣａＯ）＝４３質量％，（％ＳｉＯ2）＝１７質量％（ＣａＯ／ＳｉＯ2＝２．５），（％Ｔ．Ｆｅ）＝１５質量％，（％Ａｌ2Ｏ3）＝５質量％，（％ＭｎＯ）＝６質量％，（％Ｐ2Ｏ5）＝１．８質量％，（％ＭｇＯ）＝６質量％，（％Ｃｒ2Ｏ3）＝２質量％の組成の電気炉スラグを利用し，［％Ｐ］＝０．１００％，［Ｓｉ］＝０．３５％を含有した溶銑をＣａＯ／ＳｉＯ2＝２．０のスラグ組成にて脱硅脱燐吹錬を実施した場合の脱硅脱燐処理により発生したスラグ量に対する電気炉スラグの添加比率と必要ＣａＯ原単位比を示した図である。必要ＣａＯ原単位比は、電気炉スラグを利用しなかったときの必要ＣａＯ原単位を１として示したものである。 FIG. 1 shows, as an example, (% CaO) = 43% by mass, (% SiO 2 ) = 17% by mass (CaO / SiO 2 = 2.5), (% T.Fe) = 15% by mass, (% Al 2 O 3 ) = 5 mass%, (% MnO) = 6 mass%, (% P 2 O 5 ) = 1.8 mass%, (% MgO) = 6 mass%, (% Cr 2 O 3 ) = 2 Using an electric furnace slag having a composition of mass%, the hot metal containing [% P] = 0.100% and [Si] = 0.35% was removed with a slag composition of CaO / SiO 2 = 2.0. It is the figure which showed the addition ratio of the electric furnace slag with respect to the amount of slag generate | occur | produced by the dephosphorization dephosphorization process at the time of implementing dephosphorization, and required CaO basic unit ratio. The required CaO basic unit ratio indicates the required CaO basic unit when the electric furnace slag is not used as 1.
図１が示すように、電気炉スラグ添加比率の上昇にともなってＣａＯ原単位比率は低下し，電気炉スラグ比率を４０％とすることで，電気炉スラグを使用しない場合（全量ＣａＯ使用）に比べ約１割のＣａＯ原単位の削減が可能となる。 As shown in FIG. 1, the CaO unit ratio decreases as the electric furnace slag addition ratio increases, and the electric furnace slag ratio is set to 40%, so that the electric furnace slag is not used (total amount of CaO used). Compared to about 10% of the CaO basic unit can be reduced.
図２は、図１と同一の条件にて電気炉スラグを転炉での脱硅脱燐処理に利用した際の該処理により発生したスラグ量に対する電気炉スラグの添加比率と脱燐率の関係を示した図である。 FIG. 2 shows the relationship between the addition ratio of the electric furnace slag and the dephosphorization rate with respect to the amount of slag generated when the electric furnace slag is used for the degassing and dephosphorization process in the converter under the same conditions as FIG. FIG.
図２が示すように、電気炉スラグ比率５％未満では，全量ＣａＯを用いて脱燐処理を行った場合に比べ脱燐率の向上は認められない。これは添加する電気炉スラグ量が少なくＣａＯ滓化促進の効果が不十分であるためである。逆に電気炉スラグ比率が３０％を越えると脱燐率の低下が見られるが，これは電気炉スラグ添加によるスラグ量自体の増加に起因して攪拌が不十分となることや電気炉スラグ中に含まれるＰ2Ｏ5に起因してスラグ中のＰ2Ｏ5の物質移動が阻害されるためである。 As shown in FIG. 2, when the electric furnace slag ratio is less than 5%, an improvement in the dephosphorization rate is not observed as compared with the case where the dephosphorization treatment is performed using the total amount of CaO. This is because the amount of electric furnace slag to be added is small and the effect of promoting CaO hatching is insufficient. Conversely, when the electric furnace slag ratio exceeds 30%, the dephosphorization rate decreases, but this is due to the increase in the amount of slag itself due to the addition of the electric furnace slag, and the lack of stirring. This is because the mass transfer of P 2 O 5 in the slag is inhibited due to P 2 O 5 contained in the slag.
さらに電気炉スラグ比率が３０％を超えるような場合では，脱燐処理時のスラグ量自体が膨大となってしまうため，脱燐処理時のスロッピング発生頻度が増えるなどの操業性の悪化起因となる場合がある。 Furthermore, when the electric furnace slag ratio exceeds 30%, the amount of slag during the dephosphorization process itself will be enormous, which may lead to a deterioration in operability such as increased frequency of slopping during the dephosphorization process. There is a case.
ここで，脱燐率とは処理前［Ｐ］濃度に対して，処理後に溶銑から除去された［Ｐ］濃度との割合を示す指標で，下記（１）式で表される。
脱燐率(％)＝{(処理前[％Ｐ]−処理後[％Ｐ])／処理前[％Ｐ]}×100 ・・・（１）
Here, the dephosphorization rate is an index indicating the ratio of the [P] concentration removed from the hot metal after the treatment to the [P] concentration before the treatment, and is expressed by the following equation (1).
Dephosphorization rate (%) = {(before treatment [% P] −after treatment [% P]) / before treatment [% P]} × 100 (1)
したがって，脱燐処理時に添加する電気炉スラグ量の比率としては，５％〜３０％の範囲が望ましい。 Therefore, the ratio of the electric furnace slag amount to be added during the dephosphorization process is desirably in the range of 5% to 30%.
電気炉スラグを転炉に投入するタイミングとしては，脱硅脱燐処理の開始から終了までの時間において該処理開始後の７０％〜９０％の時期とすることが望ましい。これは，電気炉スラグの添加量が適正範囲であっても、脱硅脱燐処理の吹錬期間初期から中期（０％〜７０％）にかけて電気炉スラグを添加すると，スラグ滓化の良好な期間が長時間となりスロッピングなどの操業阻害を招くため操業の安定化のためには多量のフォーミング鎮静剤を投入する必要が生じるためであり，逆に吹錬が９０％以上経過した末期の段階での添加では，終了までの時間が短すぎるため滓化不良を引き起こし，結果として脱燐効率の悪化を招くためである。 The timing for charging the electric furnace slag into the converter is preferably 70% to 90% after the start of the dephosphorization / dephosphorization process. Even if the addition amount of the electric furnace slag is within the proper range, if the electric furnace slag is added from the early stage to the middle stage (0% to 70%) of the degassing and dephosphorization treatment, the slag hatching is good. This is because a long period of time causes an operational hindrance such as slopping, so it is necessary to add a large amount of foaming sedative to stabilize the operation, and conversely, the final stage when 90% or more of blowing has passed. This is because the time until completion is too short to cause hatching failure, resulting in deterioration of dephosphorization efficiency.
本発明の効果を実施例によって説明する。 The effects of the present invention will be described with reference to examples.
電気炉にて溶解・酸化精錬を行い出滓した，（％ＣａＯ）＝４３質量％，（％ＳｉＯ2）＝１７質量％（ＣａＯ／ＳｉＯ2＝２．５），（％Ｔ．Ｆｅ）＝１５質量％，（％Ａｌ2Ｏ3）＝５質量％，（％ＭｎＯ）＝６質量％，（％Ｐ2Ｏ5）＝１．８質量％，（％ＭｇＯ）＝６質量％，（％Ｃｒ2Ｏ3）＝２質量％の組成を有し、ｆ．ＣａＯ＝１．４質量％を含有する電気炉スラグを破砕し，乾燥後に転炉炉上に搬送し，転炉にての脱珪脱燐処理時に利用した。破砕後の電気炉スラグの平均粒径は３０ｍｍ程度であった。 It was obtained by melting and oxidizing refining in an electric furnace, (% CaO) = 43% by mass, (% SiO 2 ) = 17% by mass (CaO / SiO 2 = 2.5), (% T.Fe) = 15% by mass, (% Al 2 O 3 ) = 5% by mass, (% MnO) = 6% by mass, (% P 2 O 5 ) = 1.8% by mass, (% MgO) = 6% by mass, (% Cr 2 O 3 ) = 2% by mass, f. The electric furnace slag containing CaO = 1.4% by mass was crushed, dried and transported to the converter, and used for desiliconization and dephosphorization in the converter. The average particle diameter of the electric furnace slag after crushing was about 30 mm.
転炉での脱珪脱隣処理については、転炉への溶銑装入量が２８０トン、装入溶銑中のＣ濃度は４．５質量％程度、Ｓｉ濃度は０．４質量％程度であり、脱珪脱隣処理終了時の溶銑中のＣ濃度は３．９質量％程度、Ｓｉ濃度は０．０１質量％以下であった。 Regarding desiliconization and de-neighboring treatment in the converter, the amount of molten metal charged into the converter is 280 tons, the C concentration in the charged molten iron is about 4.5 mass%, and the Si concentration is about 0.4 mass%. The C concentration in the hot metal at the end of the desiliconization and adjacent processing was about 3.9% by mass, and the Si concentration was 0.01% by mass or less.
脱珪脱燐処理により発生したスラグ量については、脱珪脱燐処理後にスラグを転炉からスラグパンに排出して秤量した。添加した電気炉スラグ量を発生スラグ量で除することにより、電気炉スラグ添加比率（％）を算出した。 About the amount of slag generated by the desiliconization and dephosphorization treatment, the slag was discharged from the converter to the slag pan after the desiliconization and dephosphorization treatment and weighed. The electric furnace slag addition ratio (%) was calculated by dividing the added electric furnace slag amount by the generated slag amount.
その結果を表１の発明例１〜８に示す。ＣａＯ原単位指数とは、比較例９のＣａＯ原単位を１として相対的に表示したＣａＯ原単位を意味する。ちなみに、比較例９のＣａＯ原単位は１７ｋｇ／ｔｏｎであった。いずれも電気炉スラグの利用によりＣａＯ原単位を削減しつつ高い脱燐効率を示す結果が得られており，スロッピングなどの操業性の悪化を引き起こすことなく、安定した操業が達成されている。 The results are shown in Invention Examples 1 to 8 in Table 1. The CaO basic unit index means a CaO basic unit that is relatively displayed with the CaO basic unit of Comparative Example 9 as 1. Incidentally, the CaO basic unit of Comparative Example 9 was 17 kg / ton. In both cases, the use of electric furnace slag has resulted in high dephosphorization efficiency while reducing the basic unit of CaO, and stable operation has been achieved without causing deterioration of operability such as slopping.
これに対し，比較例９は電気炉スラグの利用を全く行わず全量ＣａＯによる脱燐処理を行ったものであるが，ＣａＯ原単位の削減が達成されないことに加え、スラグ滓化が不十分であることに起因して脱燐効率が向上せず低燐鋼の溶製が困難であるという結果となっている。また，比較例１０においては電気炉スラグの添加比率が低いことに起因して脱燐処理時のスラグ滓化が不十分となり結果的に脱燐効率が悪く，低燐鋼の安定溶製が困難となっている。比較例１１は電気炉スラグの添加比率が高く、ＣａＯ原単位の削減は十分ではあるものの，スラグ量自体の増加に起因して攪拌が不十分となることに起因して脱燐効率の低下が見られている。さらに比較例１２では，電気炉スラグの添加比率は適正であるものの，添加タイミングが早すぎるため吹錬中スラグのフォーミング期間が長く，結果的にスロッピングを引き起こし操業性を阻害する結果となっている。また，比較例１３においては，逆に電気炉スラグの添加タイミングが遅れ十分なスラグ滓化の時間が確保できないためにスラグ滓化が不十分となり脱燐効率の悪化を引き起こす結果となっている。 On the other hand, Comparative Example 9 does not use the electric furnace slag at all and performs the dephosphorization treatment with the whole amount of CaO. However, in addition to the fact that the reduction of the CaO basic unit cannot be achieved, the slag hatching is insufficient. As a result, the dephosphorization efficiency is not improved, and it is difficult to melt the low phosphorus steel. Further, in Comparative Example 10, due to the low addition ratio of the electric furnace slag, the slag hatching during the dephosphorization treatment becomes insufficient, resulting in poor dephosphorization efficiency, and it is difficult to stably melt low phosphorus steel. It has become. In Comparative Example 11, although the addition ratio of electric furnace slag is high and the reduction of the basic unit of CaO is sufficient, the dephosphorization efficiency is lowered due to insufficient stirring due to the increase in the amount of slag itself. It has been seen. Furthermore, in Comparative Example 12, although the addition ratio of the electric furnace slag is appropriate, the addition timing is too early, so the slag forming period is long during blowing, resulting in slopping and hindering operability. Yes. In Comparative Example 13, on the contrary, the addition timing of the electric furnace slag is delayed and sufficient slag hatching time cannot be secured, so that slag hatching becomes insufficient and dephosphorization efficiency is deteriorated.
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