JP4582826B2 - Manufacturing method of clean steel with RH degassing equipment - Google Patents
Manufacturing method of clean steel with RH degassing equipment Download PDFInfo
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- JP4582826B2 JP4582826B2 JP24891197A JP24891197A JP4582826B2 JP 4582826 B2 JP4582826 B2 JP 4582826B2 JP 24891197 A JP24891197 A JP 24891197A JP 24891197 A JP24891197 A JP 24891197A JP 4582826 B2 JP4582826 B2 JP 4582826B2
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Description
【0001】
【発明の属する技術分野】
本発明は、RH脱ガス装置を用いて、脱酸生成物である酸化物系介在物の少ない清浄鋼を安定して製造する方法に関するものである。
【0002】
【従来の技術】
近年の鉄鋼材料の高機能化及び高品質化への要求の高まりから、燐、硫黄等の不純物元素や、脱酸生成物、転炉スラグ及びモールドパウダー等を起源とする酸化物系介在物を極力低減することが要望されている。この内、酸化物系介在物は薄鋼板製品での表面欠陥の主原因となるため、精錬から鋳造に至るまでに数々の低減対策が実施されており、特にAl2O3系の脱酸生成物を起源とする酸化物系介在物(以下、「介在物」と記す)はRH脱ガス処理により効率良く低減されるので、RH脱ガス装置を用いた介在物の低減方法が多数提案されている。
【0003】
例えば、特開昭57−200514号公報には、上昇側浸漬管に環流ガスを吹き込むと共に、上昇側浸漬管直下の取鍋底からもArガスを吹き込み、取鍋底から吹き込むArガスにて、取鍋内溶鋼の攪拌と真空槽を環流する溶鋼量を増大させて溶鋼の環流率を上昇し、RH脱ガス装置による低減効果を向上させた方法が開示されている。
【0004】
又、特開平9−49012号公報には、Al脱酸後、真空槽内の溶鋼中に、CaOを主体とする粒径0.1〜10mmのフラックスを取鍋内溶鋼上に存在するスラグ量に応じて添加し、Al脱酸により発生する介在物を効率良く低減する方法が開示されている。
【0005】
【発明が解決しようとする課題】
上記の特開昭57−200514号公報、及び、特開平9−49012号公報に記載の方法は、介在物の除去に有効な手段ではあるが、脱酸後にどの程度の時間、処理を継続すれば介在物の浮上分離が完了するのかが不明であり、そのため、脱酸後の処理時間が短か過ぎて介在物の浮上分離が十分でない場合や、逆に、処理時間が延長して溶鋼温度が低下しすぎ、次工程でトラブルの生じる場合もあった。
【0006】
本発明は、上記事情に鑑みなされたもので、その目的は、溶鋼中に発生する介在物量に応じて脱酸後の処理時間を決め、介在物の少ない清浄鋼をRH脱ガス装置で安定して製造する方法を提供することである。
【0007】
【課題を解決するための手段】
本発明によるRH脱ガス装置での清浄鋼の製造方法は、環流用Arガスにより溶鋼を真空槽内へ環流しつつ、真空槽内でAlを添加して未脱酸状態の溶鋼を脱酸し、その後、真空槽内への環流を継続した後に処理を終えるRH脱ガス装置での精錬の際に、Al添加直前での溶鋼中の溶解酸素量Coを測定し、測定された前記溶鋼中の溶解酸素量Coと、上昇側浸漬管に吹き込まれる環流用Arガス量Qとから、(1)式を用いてAl添加後の処理時間tを決めることを特徴とするものである。
【0008】
t≧20×(1−0.5Co/50)×(8/Q)0.5 ……(1)
但し、(1)式において各記号は以下を表わすものである。
【0009】
t :Al添加後の処理時間(min)
Co:溶解酸素量(ppm)
Q :環流用Arガス量(Nl/min・ton)
発明者等は、RH脱ガス装置において未脱酸鋼を脱酸する際に、Al添加直前の溶鋼中の溶解酸素量Coと、Al添加後に上昇側浸漬管に吹き込むArガス量Qと、Al添加後の処理時間tとを様々に変更して、これらの要因とAl脱酸により生成するAl2O3系介在物の量との関係を調査した。
【0010】
その結果、図2に示すように、溶解酸素量Coと環流用Arガス量Qとで決まる(1)式の右辺より、Al添加後の処理時間tを長くすることで、介在物が処理中に十分浮上・分離して減少し、製品での介在物による表面欠陥指数が低下することが確認できた。これは、脱酸直後の溶鋼中介在物量は、脱酸直前の溶解酸素量Coに依存し、そして、生成した介在物は、その発生時から環流ガスのArガス量Qに比例して時間と共に減少するので、溶解酸素量Coと環流用Arガス量Qとで構成される(1)式右辺により、脱酸後の処理時間を決めることができるからである。
【0011】
【発明の実施の形態】
本発明を図面に基づき説明する。図1は、本発明を実施したRH脱ガス装置の断面概略図である。
【0012】
図において、上昇側浸漬管2と下降側浸漬管3とを下部に備え、上部で排気装置(図示せず)に連結された真空槽1を主設備として構築されるRH脱ガス装置の直下に、転炉(図示せず)から出鋼され、スラグ8と未脱酸状態の溶鋼6とを収納した取鍋7が搬入されている。そして、取鍋7を昇降装置(図示せず)により上昇させて取鍋7内の溶鋼6を上昇側浸漬管2及び下降側浸漬管3に浸漬し、上昇側浸漬管2を貫通して設けた環流用Arガス吹き込み管4から上昇側浸漬管2内にArガスを吹き込むと共に、真空槽1内を排気装置にて排気すると、取鍋7内の溶鋼6は、Arガス気泡9と共に上昇側浸漬管2を上昇して真空槽1内に流入し、その後、下降側浸漬管3から取鍋7に戻る流れ、所謂、環流を形成してRH脱ガス処理が施される。
【0013】
こうして、未脱酸状態の溶鋼6を、例えば真空脱炭処理等で所定時間処理した後、溶鋼6中の溶解酸素量Co(ppm)を測定し、次いで、この溶解酸素量Coに応じて溶鋼6中に0.01〜0.05wt%のAlが残留する程度の量の金属Alを、真空槽1の側壁を貫通して設けた原料投入口5から真空槽1内に添加して溶鋼6を脱酸する。添加後残留するAlの含有量が0.01wt%未満では脱酸が弱く、又、0.05wt%を超える過剰のAlはコスト上不利益であるからである。尚、溶解酸素量Coの測定は、周知の方法、例えば酸素プローブを溶鋼6に浸漬して直接測定する方法や、溶鋼6から採取した試料を化学分析して求める方法等で行えば良い。
【0014】
そして、把握した溶解酸素量Co(ppm)と、Al添加後に吹き込まれる環流用Arガス量Q(Nl/min・ton)とを(1)式に代入して(1)式右辺を算出し、(1)式右辺で算出される時間(min)以上の処理時間tでAl添加後継続して処理した後に、環流用Arガスの吹き込みと真空槽1内の排気を停止してRH脱ガス処理を終了する。尚、本発明の環流用Arガス量Qは、1分間当たりに上昇側浸漬管に吹き込まれるArガス流量(Nl/min)を処理する溶鋼のヒート量(ton)で除算した値である。
【0015】
その際に、Al添加後の真空槽1内の圧力は5torr以下に維持することが好ましい。真空槽1内の圧力が5torrを超えると、溶鋼6の環流量が低下して介在物の浮上・分離が妨げられるからである。
【0016】
このようにしてRH脱ガス処理を施すことで、Al脱酸により発生する介在物の量に関わらず、介在物の少ない清浄鋼を安定して製造することができる。
【0017】
尚、取鍋7内のスラグ8は、転炉出鋼時に転炉スラグが混入したものであり、通常、FeOやMnO等の低級酸化物を含む。これら低級酸化物は、RH脱ガス装置でのAl脱酸後に溶鋼6中に溶解するAlと反応して、Al2O3を新たに生成させ、溶鋼6の清浄性を劣化させる。そのため、清浄鋼を製造する際には、転炉スラグの混入を防止したり、取鍋7内のスラグ8に金属Al、又はCaOを主成分とするスラグ改質剤等を添加し、スラグ8中の(%T.Fe)と(%MnO)との合計を4wt%以下に低減してから、RH脱ガス処理を実施することが好ましい。尚、(T.Fe)とは、全ての鉄酸化物(FeOやFe2O3等)を表わしている。
【0018】
【実施例】
図1に示すRH脱ガス装置を用いて、転炉から出鋼された未脱酸鋼を脱酸する際に、Al添加直前の溶鋼中の溶解酸素量Coを測定し、Al添加後に上昇側浸漬管に吹き込むArガス量QとAl添加後の処理時間tとを様々に変更して、合計35ヒートの試験操業を実施し、前記溶解酸素量CoとArガス量QとAl添加後の処理時間tとが、Al脱酸により生成するAl2O3系介在物の浮上・分離に及ぼす影響を調査した。
【0019】
対象とした溶鋼はC含有量が0.02〜0.06wt%の未脱酸溶鋼で、転炉からの出鋼量を250tonと300tonの2水準で実施した。そして、全てのヒートで転炉出鋼後、取鍋内スラグにCaOを主成分とするスラグ改質剤を添加し、スラグ中の(%T.Fe)と(%MnO)との合計を4wt%以下に予め調整した。調整後のスラグ組成は、CaO−SiO2−Al2O3−MgO系である。
【0020】
未脱酸状態で所定の時間処理した後、溶解酸素量Coを酸素プローブにて測定し、測定した溶解酸素量Coに応じて溶鋼中のAl含有量が0.01〜0.05wt%となる量の金属Alを真空槽に投入して溶鋼を脱酸した。
【0021】
Al脱酸後、上昇側浸漬管内に環流用Arガスを、Arガス量Qが8〜24Nl/min・ton、具体的にはヒート量が250tonの場合に2000〜6000Nl/minの範囲で吹き込みつつ、真空槽内の圧力を0.5〜2torrに制御して処理を継続し、Al添加後10〜15分間でRH脱ガス処理を終了した。
【0022】
そして、RH脱ガス処理後、スラブ連続鋳造機にて厚み220mm、幅950mmの鋳片に鋳造し、得られた鋳片を熱間圧延、次いで冷間圧延して最終的に薄鋼板製品として、薄鋼板製品において介在物による表面欠陥を調査した。尚、表面欠陥の程度は指数化して表示し、表面欠陥指数が低い程介在物が少ないことを表わしている。
【0023】
表1に、35ヒートの試験操業におけるRH脱ガス処理でのヒート量、測定した溶解酸素量Co、環流用Arガス量Q、Al添加後の処理時間t、及び、製品での表面欠陥指数をまとめて示す。但し、環流用Arガス量Qの欄のカッコ内数値は単位時間当たりのArガス流量(Nl/min)を示す。表1に示すようにAl脱酸前の溶解酸素量Coが比較的少ないにもかかわらず製品での表面欠陥指数が高いヒート(例えば、テストNo.1)や、逆に、溶解酸素量Coは多いにもかかわらず製品での表面欠陥指数が低いヒート(例えば、テストNo.23)がある。
【0024】
【表1】
【0025】
Al添加により生成した介在物をRH脱ガス処理中に溶鋼中から浮上・分離させるための要因として以下の2つの前提を立て、次元解析的な手法により製品の表面欠陥指数が0のヒートと、それ以外のヒートとを区分することができる式を考え、そして前述の(1)式として提案した。
前提(1):溶解酸素量Coが高い程、Al脱酸後の処理時間tを延長する必要がある。
前提(2):環流用Arガス量Qが多い程、介在物の浮上・分離が促進されて処理時間tは短くすることができる。
【0026】
表1には、各ヒートの溶解酸素量Coと環流用Arガス量Qとで算出された(1)式右辺の値と、実際の処理時間tとの比を合わせて示す。そして、処理時間tと算出された(1)式右辺との比を横軸とし、製品表面欠陥指数を縦軸としてグラフ化したものが図2である。図2に示すように、(1)式右辺による処理時間より実際の処理時間tが長い全てのヒートでは、製品欠陥指数は0であり、従って、少なくとも(1)式の右辺から算出される時間より長い時間、Al添加後処理することで、介在物を浮上・分離させ、清浄鋼の製造が可能であることが知見された。尚、表1の備考欄に本発明の範囲内のヒートを実施例として、又、それ以外のヒートを比較例として区分して表示した。
【0027】
【発明の効果】
本発明では、溶鋼中の溶解酸素量を把握した上でAl脱酸し、そして、Al脱酸後の処理時間を前記溶解酸素量と環流用Arガス量とで算出される適切な時間以上とするので、Al脱酸により生成する介在物をRH脱ガス処理中に溶鋼中から浮上・分離させ、安定して清浄鋼を製造することができる。
【図面の簡単な説明】
【図1】本発明を実施したRH脱ガス装置の断面概略図である。
【図2】試験操業による製品表面欠陥の調査結果を(1)式により整理して示した図である。
【符号の説明】
1 真空槽
2 上昇側浸漬管
3 下降側浸漬管
4 環流用Arガス吹き込み管
5 原料投入口
6 溶鋼
7 取鍋
8 スラグ
9 Arガス気泡[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for stably producing clean steel with a small amount of oxide inclusions, which are deoxidation products, using an RH degassing apparatus.
[0002]
[Prior art]
Due to the increasing demand for higher functionality and higher quality of steel materials in recent years, impurity elements such as phosphorus and sulfur, oxide inclusions originating from deoxidation products, converter slag, mold powder, etc. It is desired to reduce as much as possible. Among these, oxide inclusions are the main cause of surface defects in thin steel sheet products, and therefore, various reduction measures have been implemented from refining to casting, especially deoxidation generation of Al 2 O 3 series. Since oxide inclusions (hereinafter referred to as “inclusions”) originating from the inclusions are efficiently reduced by the RH degassing treatment, many methods for reducing inclusions using an RH degassing apparatus have been proposed. Yes.
[0003]
For example, Japanese Patent Laid-Open No. 57-200514 discloses that a reflux gas is blown into the ascending side dip tube, and Ar gas is also blown from the bottom of the ladle directly below the ascending side dip tube. A method is disclosed in which the agitation of the inner molten steel and the amount of molten steel circulating in the vacuum chamber are increased to increase the reflux rate of the molten steel, and the reduction effect by the RH degassing apparatus is improved.
[0004]
Japanese Patent Laid-Open No. 9-49012 discloses that the amount of slag present on the molten steel in the ladle with a flux having a particle size of 0.1 to 10 mm mainly composed of CaO in the molten steel in the vacuum chamber after Al deoxidation. A method is disclosed in which inclusions generated by Al deoxidation are efficiently reduced.
[0005]
[Problems to be solved by the invention]
The methods described in JP-A-57-2000514 and JP-A-9-49012 are effective means for removing inclusions, but how long the treatment can be continued after deoxidation. For example, it is unclear whether the floating separation of inclusions is complete, so if the processing time after deoxidation is too short and the floating separation of inclusions is not sufficient, or conversely, the processing time is extended and the molten steel temperature In some cases, troubles occurred in the next process.
[0006]
The present invention has been made in view of the above circumstances, and its purpose is to determine the treatment time after deoxidation according to the amount of inclusions generated in molten steel, and to stabilize clean steel with few inclusions with an RH degasser. It is to provide a manufacturing method.
[0007]
[Means for Solving the Problems]
The method for producing clean steel in the RH degassing apparatus according to the present invention is to deoxidize molten steel in an undeoxidized state by adding Al in the vacuum tank while circulating the molten steel into the vacuum tank with the refluxing Ar gas. Then, at the time of refining in the RH degassing apparatus which finishes the treatment after continuing the reflux into the vacuum chamber, the amount of dissolved oxygen Co in the molten steel immediately before the addition of Al is measured, and the measured The processing time t after the addition of Al is determined by using the equation (1) from the dissolved oxygen amount Co and the circulating Ar gas amount Q blown into the rising side dip tube.
[0008]
t ≧ 20 × (1-0.5 Co / 50 ) × (8 / Q) 0.5 (1)
However, in the equation (1), each symbol represents the following.
[0009]
t: Processing time after addition of Al (min)
Co: dissolved oxygen amount (ppm)
Q: Ar gas amount for reflux (Nl / min · ton)
The inventors, when deoxidizing non-deoxidized steel in the RH degassing apparatus, the amount of dissolved oxygen Co in the molten steel immediately before the addition of Al, the amount of Ar gas Q blown into the rising side dip tube after the addition of Al, and Al The treatment time t after the addition was variously changed, and the relationship between these factors and the amount of Al 2 O 3 inclusions generated by Al deoxidation was investigated.
[0010]
As a result, as shown in FIG. 2, by increasing the treatment time t after the addition of Al from the right side of the equation (1) determined by the dissolved oxygen amount Co and the circulating Ar gas amount Q, the inclusions are being processed. It was confirmed that the surface defect index due to inclusions in the product decreased. This is because the amount of inclusions in the molten steel immediately after deoxidation depends on the dissolved oxygen amount Co immediately before deoxidation, and the generated inclusions are proportional to the amount of Ar gas Q in the reflux gas from the time of occurrence. This is because the processing time after deoxidation can be determined by the right side of the formula (1) configured by the dissolved oxygen amount Co and the circulating Ar gas amount Q.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an RH degassing apparatus embodying the present invention.
[0012]
In the figure, an ascending-
[0013]
Thus, after the undeoxidized molten steel 6 is treated for a predetermined time by, for example, vacuum decarburization, the amount of dissolved oxygen Co (ppm) in the molten steel 6 is measured, and then the molten steel according to the dissolved oxygen amount Co. Metal Al in such an amount that 0.01 to 0.05 wt% of Al remains in the steel 6 is added into the
[0014]
Then, by substituting the grasped dissolved oxygen amount Co (ppm) and the circulating Ar gas amount Q (Nl / min · ton) blown after the addition of Al into the equation (1), the right side of the equation (1) is calculated, (1) The RH degassing process is performed by continuously blowing Ar gas for reflux and exhausting the
[0015]
At that time, it is preferable to maintain the pressure in the
[0016]
By performing the RH degassing treatment in this way, it is possible to stably produce clean steel with few inclusions regardless of the amount of inclusions generated by Al deoxidation.
[0017]
In addition, the
[0018]
【Example】
When deoxidizing undeoxidized steel produced from a converter using the RH degassing apparatus shown in FIG. 1, the amount of dissolved oxygen Co in the molten steel immediately before the addition of Al is measured. The Ar gas amount Q blown into the dip tube and the treatment time t after the addition of Al were variously changed, and a test operation of a total of 35 heats was carried out. The treatment after the dissolved oxygen amount Co, the Ar gas amount Q and the Al addition The effect of time t on the floating and separation of Al 2 O 3 inclusions generated by Al deoxidation was investigated.
[0019]
The target molten steel was non-deoxidized molten steel having a C content of 0.02 to 0.06 wt%, and the steel output from the converter was implemented at two levels of 250 ton and 300 ton. And after the converter steel is output by all heats, the slag modifier which has CaO as a main component is added to the slag in a ladle, and the sum total of (% T.Fe) and (% MnO) in slag is 4 wt. % Previously adjusted. The adjusted slag composition is CaO—SiO 2 —Al 2 O 3 —MgO.
[0020]
After processing for a predetermined time in an undeoxidized state, the dissolved oxygen amount Co is measured with an oxygen probe, and the Al content in the molten steel becomes 0.01 to 0.05 wt% according to the measured dissolved oxygen amount Co. An amount of metal Al was put into a vacuum chamber to deoxidize the molten steel.
[0021]
After deoxidizing Al, circulating Ar gas is blown into the ascending-side dip tube while Ar gas amount Q is 8 to 24 Nl / min · ton, specifically, when the heat amount is 250 ton, 2000 to 6000 Nl / min. The process was continued by controlling the pressure in the vacuum chamber to 0.5 to 2 torr, and the RH degassing process was completed in 10 to 15 minutes after the addition of Al.
[0022]
Then, after RH degassing treatment, cast into a slab having a thickness of 220 mm and a width of 950 mm with a slab continuous casting machine, and the obtained slab is hot-rolled and then cold-rolled to finally produce a steel sheet product, Surface defects due to inclusions were investigated in thin steel sheet products. The degree of surface defects is indexed and displayed, and the lower the surface defect index, the less inclusions.
[0023]
Table 1 shows the heat amount in the RH degassing process in the 35 heat test operation, the measured dissolved oxygen amount Co, the Ar gas amount Q for refluxing, the treatment time t after the addition of Al, and the surface defect index in the product. Shown together. However, the numerical value in parentheses in the column of the amount of Ar gas for reflux Q indicates the Ar gas flow rate (Nl / min) per unit time. As shown in Table 1, although the dissolved oxygen amount Co before Al deoxidation is relatively small, the product has a high surface defect index (for example, test No. 1), and conversely, the dissolved oxygen amount Co is There is a heat (for example, test No. 23) with a low surface defect index in the product despite the large number.
[0024]
[Table 1]
[0025]
The following two assumptions are made as factors for causing inclusions generated by the addition of Al to float and separate from the molten steel during the RH degassing process, and heat with a product surface defect index of 0 by a dimensional analysis method, A formula that can be distinguished from other heats was considered and proposed as formula (1) above.
Assumption (1): It is necessary to extend the treatment time t after Al deoxidation as the dissolved oxygen amount Co increases.
Assumption (2): Increasing the amount Q of Ar gas for recirculation promotes the floating and separation of inclusions, and the processing time t can be shortened.
[0026]
Table 1 also shows the ratio of the value on the right side of the equation (1) calculated from the dissolved oxygen amount Co and the refluxing Ar gas amount Q for each heat and the actual processing time t. FIG. 2 is a graph in which the ratio between the processing time t and the calculated right side of equation (1) is plotted on the horizontal axis and the product surface defect index is plotted on the vertical axis. As shown in FIG. 2, in all heats in which the actual processing time t is longer than the processing time according to the right side of the equation (1), the product defect index is 0. Therefore, the time calculated from at least the right side of the equation (1) It was discovered that inclusions were levitated and separated by treatment after addition of Al for a longer time, and it was possible to produce clean steel. In addition, in the remarks column of Table 1, the heat within the range of the present invention is classified and displayed as an example, and the other heat is classified and displayed as a comparative example.
[0027]
【The invention's effect】
In the present invention, Al is deoxidized after grasping the amount of dissolved oxygen in the molten steel, and the treatment time after Al deoxidation is not less than an appropriate time calculated from the amount of dissolved oxygen and the amount of Ar gas for reflux. Therefore, inclusions generated by Al deoxidation can be floated and separated from the molten steel during the RH degassing process, and clean steel can be manufactured stably.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an RH degassing apparatus embodying the present invention.
FIG. 2 is a diagram showing the investigation results of product surface defects by a test operation, organized by equation (1).
[Explanation of symbols]
DESCRIPTION OF
Claims (1)
t≧20×(1−0.5Co/50)×(8/Q)0.5 ……(1)
但し、(1)式において各記号は以下を表わすものである。
t :Al添加後の処理時間(min)
Co:溶解酸素量(ppm)
Q :環流用Arガス量(Nl/min・ton)While circulating the molten steel into the vacuum chamber with the Ar gas for recirculation, Al is added in the vacuum chamber to deoxidize the molten steel in an undeoxidized state, and then the processing is finished after continuing the reflux into the vacuum chamber. During refining in the RH degassing apparatus, the dissolved oxygen amount Co in the molten steel immediately before the addition of Al is measured, and the measured dissolved oxygen amount Co in the molten steel and the Ar for reflux that is blown into the rising side dip pipe A method for producing clean steel in an RH degassing apparatus, wherein the processing time t after addition of Al is determined from the gas amount Q using the equation (1) .
t ≧ 20 × (1-0.5 Co / 50 ) × (8 / Q) 0.5 (1)
However, in the equation (1), each symbol represents the following.
t: Processing time after addition of Al (min)
Co: dissolved oxygen amount (ppm)
Q: Ar gas amount for reflux (Nl / min · ton)
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JP24891197A JP4582826B2 (en) | 1997-09-12 | 1997-09-12 | Manufacturing method of clean steel with RH degassing equipment |
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JP24891197A JP4582826B2 (en) | 1997-09-12 | 1997-09-12 | Manufacturing method of clean steel with RH degassing equipment |
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JP5428447B2 (en) * | 2008-03-31 | 2014-02-26 | Jfeスチール株式会社 | Method for refining molten steel in RH vacuum degassing equipment |
TWI593803B (en) * | 2012-01-27 | 2017-08-01 | 杰富意鋼鐵股份有限公司 | Melting method of high cleanness steel |
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