JP3594757B2

JP3594757B2 - Melting method for high purity high Ni molten steel

Info

Publication number: JP3594757B2
Application number: JP03730697A
Authority: JP
Inventors: 淳長谷川; 祐志富田; 隆康原
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 1996-03-08
Filing date: 1997-02-21
Publication date: 2004-12-02
Anticipated expiration: 2017-02-21
Also published as: JPH09296210A

Description

【０００１】
【産業上の利用分野】
本発明は、Ａｌ，Ｓｉ脱酸による二次精錬で高純度高Ｎｉ鋼を溶製する方法に関する。
【０００２】
【従来の技術】
低熱膨張特性，磁気特性等を活用してシャドウマスク用材料，リードフレーム材料，磁性材料，封着合金，低温用構造物等として使用される材料として、たとえばＮｉ含有量が３０〜５０重量％の高純度Ｎｉ鋼やＦｅ−Ｎｉ合金（以下、高純度Ｎｉ鋼で総称する）が製造されている。高純度高Ｎｉ鋼を工業的規模で製造する場合、Ｆｅ及びＮｉの主要成分以外に不純物が不可避的に混入する。意図的に合金成分を添加することもあるが、特別な理由のある規格値を有する合金成分以外の元素，たとえばＣ，Ｓｉ，Ｐ，Ｓ，Ａｌ，Ｏ，Ｎ等の元素が一般的に不純物として高純度Ｎｉ鋼又はＦｅ−Ｎｉ合金に混入する。
不純物含有量が多いと、種々の弊害がもたらされる。たとえば、シャドウマスク用材料では、不純物含有量の増加によって熱膨張係数が大きくなり、エッチング性も低下する。その結果、高純度高Ｎｉ鋼本来の材料特性が十分に発揮されなくなる。また、鋼製造時においても熱間加工性が低下して歩留りを下げ、製造コストを上昇させる。そのため、高純度高Ｎｉ鋼の溶製に際しては、不純物含有量を極力少なくすることが要求される。
【０００３】
なかでも極低Ｃが要求されることから、ＲＨ装置等の真空脱ガス設備を使用する二次精錬でＣ＋Ｏ→ＣＯの反応によってＣＯガスとして溶湯中のＣを除去する方法が採用されている。この精錬反応では、溶湯中に一定量以上の溶存酸素が要求されるので、必要に応じて酸素を添加している。その結果、脱炭精錬終了後に溶存酸素をｐｐｍオーダまで低減するため、Ａｌ，Ｆｅ−Ｓｉ等の添加による脱酸処理を施している。
高純度高Ｎｉ鋼をＡｌ脱酸すると、脱酸生成物であるＡｌ_２Ｏ_３は、二次精錬中に取鍋スラグに吸着され、溶湯中に残存することはない。しかし、脱酸に消費されなかったＡｌは、溶湯に残留し、鋳造工程への移動中や鋳造中に空気中の酸素と反応し、再酸化して再びＡｌ_２Ｏ_３を生成する。その結果、得られた鋳片等にＡｌ_２Ｏ_３系介在物が残留し、製品表面に疵を発生させる原因となる。
Ａｌ_２Ｏ_３系介在物に起因する悪影響を回避するためには、Ｆｅ−Ｓｉ等のＳｉ添加剤を使用した脱酸が採用される。Ｓｉ脱酸では、ある程度のレベルまで脱酸反応が進行するが、脱酸生成物であるＳｉＯ_２が浮上しないとそれ以上に脱酸が進行しない。ＳｉＯ_２の浮上を促進させるためには、取鍋スラグのＳｉＯ_２活量を低減することが要求される。そのため、ＣａＯやＣａＦ_２等のスラグ成分調整剤を溶鋼に添加して取鍋スラグのＳｉＯ_２活量を低減させることにより、初めて１０ｐｐｍ程度まで脱酸が進行する。
【０００４】
【発明が解決しようとする課題】
Ｓｉ脱酸では、このように取鍋スラグのＳｉＯ_２活量を低減するために大量のＣａＯ，ＣａＦ_２等のスラグ調整剤を添加する必要がある。ＣａＦ_２等の過剰添加は、取鍋スラグの融点を下げ、耐火物を異常に損傷させ、取鍋炉壁や浸漬管の寿命を短くする原因となる。
また、Ａｌ添加のように発熱反応が利用できないことから、アーク加熱装置を備えていない二次精錬装置では温度補償を行うことができないため、必要以上に出鋼温度を上げざるを得なかった。その結果、主原料，副原料の歩留り低下や耐火物の寿命低下，電力，昇温剤の原単位上昇等の原因となっていた。
本発明は、このような問題を解消すべく案出されたものであり、Ｓｉ脱酸に先立ってＡｌ添加により溶湯中の自由酸素を低下させることにより、Ｓｉ脱酸時に発生するＳｉＯ_２量を減らしてスラグ調整剤の添加量削減を可能にすると共に、Ａｌの酸化発熱を利用して出鋼温度を過度に高く設定することなく高純度高Ｎｉ鋼を製造することを目的とする。
【０００５】
【課題を解決するための手段】
本発明の脱酸方法は、その目的を達成するため、アーク加熱装置を備えていない二次精錬装置でＣ濃度０．０１重量％以下の高純度高Ｎｉ溶鋼を製造する際、Ａｌ脱酸後で溶鋼の自由酸素濃度が０．０２重量％以上残留するようにＡｌを添加し、次いでＳｉ添加剤を添加してＳｉ脱酸することを特徴とする。Ａｌ添加は、１回又は複数回に分けて実施される。
本発明で使用される二次精錬装置としては、ＲＨ真空脱ガス装置，ＤＨ真空脱ガス装置，ＶＯＤ真空脱ガス装置等がある。
【０００６】
【作用】
本発明に従った脱酸方法では、Ｓｉ脱酸に先立ってＡｌを添加する初期脱酸を行い、溶鋼の自由酸素濃度を低減している。これにより、Ｓｉ脱酸時に自由酸素濃度が低くなり、ＳｉＯ_２の発生量が少なくなる。そのため、スラグ調整剤の添加量が減少する。また、溶鋼中酸素とＡｌとの発熱反応で発生した熱量を溶鋼の昇温に利用できるため、出鋼温度を過度に高くする必要がない。
Ａｌと自由酸素との平衡関係に温度が及ぼす影響を図１に示す。図１から、高純度高Ｎｉ鋼溶製時における一般的な二次精錬中の温度１６５０℃以下では自由酸素が０．０２重量％以上であると、平衡するＡｌ濃度が０．００１５重量％以下になることが判る。また、本発明者等による種々の実験結果から、図２にみられるように、溶鋼のＡｌ濃度が０．００２重量％以下になると、鋳造工程への移動中又は鋳造中におけるＡｌの再酸化で発生したＡｌ_２Ｏ_３系介在物が原因となって製品に表面疵を発生させることがないことが判明している。
【０００７】
【実施例】
普通鋼や特殊鋼の製造に使用されている溶銑の予備処理，ＬＤ−ＲＨ法による転炉及びＲＨ真空脱ガス装置を使用し、Ｎｉ含有量が３０〜５０重量％の範囲にある種々の高純度高Ｎｉ鋼を製造した。その代表的な操業例を以下に説明する。高純度高Ｎｉ鋼の成分目標値を、Ｃ：０．０１重量％以下，Ｓｉ：０．０５重量％以下，Ｎｉ：３５．５〜３６．５重量％，Ｐ：０．００５重量％以下，Ｓ：０．００３重量％以下，Ａｌ：０．０１重量％以下，Ｏ：５０ｐｐｍ以下，Ｎ：３０ｐｐｍ以下とし、その他の不純物成分を極力下げた３６％Ｎｉ鋼とした。
高炉溶銑６８トンを樋で脱Ｓｉ処理し、予備処理設備に移した。予備処理設備で、ソーダ灰１９ｋｇ／トン，ＣａＯ系脱Ｐ剤５６ｋｇ／トン及び酸素６．５Ｎｍ^３／トンをそれぞれインジェクションし、脱Ｓ・脱Ｐを施した。
【０００８】
予備処理した溶銑を転炉に装入し、更に純Ｎｉ３１トン，脱酸剤としてＦｅ−Ｓｉ４００ｋｇ，造滓剤，塩基度調整・脱Ｐ剤としてＣａＯ２８００ｋｇ，炉壁保護用添加剤として軽焼ドロマイト９８０ｋｇ，スラグ粘度調整剤としてＣａＦ_２４６０ｋｇ及び昇温剤としてカーボンブリケット１１５００ｋｇを装入した。装入後、酸素吹錬し、脱炭，Ｎｉ溶解，脱Ｓｉ，脱Ｐ及び脱Ｎした。
吹錬終了後に分析した結果、Ｐ，Ｓ，Ｎｉ及びＮの含有量は、何れも目標成分値の範囲に入っていており、溶鋼温度が１７００℃に上昇していた。この溶鋼を取鍋に出鋼した。出鋼段階では、造滓剤としてのＣａＯ３００ｋｇを予め取鍋内に装入しておき、取鍋内に転炉スラグが流出しないようにスラグカットした。
得られた高Ｎｉ溶鋼をＲＨ真空脱ガス設備に移し、真空脱炭した。その後、溶鋼温度を測定したところ、目標値よりも２０℃低かったので、酸素２５Ｎｍ^３を溶鋼に吹き込むと共にＡｌを５５ｋｇ添加することにより溶鋼を昇温した。昇温後の溶湯について、自由酸素を迅速分析装置で測定したところ０．０２５重量％であった。次いで、成分調整及び真空脱ガスを施した。
【０００９】
成分調整，真空脱ガス後の自由酸素を測定したところ０．０２重量％であったので、Ｆｅ−Ｓｉを１００ｋｇ添加し、溶鋼を２分間環流処理した。環流後の溶鋼を採取してＳｉ濃度を測定したところ、Ｓｉ濃度は０．０５重量％と規格範囲に入っていた。そこで、速やかにＲＨ真空槽内にＣａＯ３００ｋｇ及びＣａＦ_２２００ｋｇを添加し、脱酸用スラグを造滓した。その後、溶鋼を再度１０分間環流処理し、取鍋スラグによる脱酸を施した。ＲＨ出鍋時点で、自由酸素が０．００１重量％，Ａｌ濃度が０．００１重量％であった。
以上の各工程における溶鋼成分値，溶鋼温度，溶鋼重量及びスラグ組成を表１に示す。
【００１０】

【００１１】
表１にみられるように、ＲＨ真空脱ガス処理後の溶鋼は、各成分が目標値に達しており、溶鋼温度も適正であった。そこで、この溶鋼を連続鋳造工程で鋳造し、所定寸法形状をもつ高純度高Ｎｉ鋼素材を得た。得られた連鋳スラブの品質を調査した結果、図３及び図４に示すように介在物レベル及び表面品質レベル共に従来法で製造されたスラブとほぼ同等の性状を呈した。
また、別の試験において、処理中の温度調整のため２回又は３回、或いはそれ以上の回数でＡｌを添加したが、何れの場合も自由酸素を０．０２０重量％以上残すようにした。そのため、ＲＨ出鍋時点でＡｌ濃度が０．００２重量％以下となり、介在物及び表面品質レベルに支障を来すことがなかった。
また、Ａｌ添加により自由酸素濃度を下げた溶鋼にＦｅ−Ｓｉを装入しているので、Ｓｉ脱酸に伴ったＳｉＯ_２発生量が減少した。そのため、取鍋スラグ調整剤の添加量を低減することができ、図５に示すように、ＲＨ浸漬管の寿命を従来法に比較して約倍にすることできた。また、Ａｌ添加によって溶鋼が昇温するため、図６に示すように転炉又は電気炉の出鋼温度を約２０℃低減することが可能となった。したがって、高純度高Ｎｉ鋼を低コストで製造できることが判った。
【００１２】
【発明の効果】
以上に説明したように、本発明においては、Ｓｉ脱酸に先立ってＡｌ添加により溶鋼の自由酸素濃度を低下し、次いでＦｅ−Ｓｉ等を使用してＳｉ脱酸している。そのため、Ｓｉ脱酸時のＳｉＯ_２発生量が減少し、それに応じてスラグ調整剤の添加量を減らすことができるため、二次精錬装置の炉壁や浸漬管の寿命が長くなり、製造コストが低減される。また、Ａｌの酸化発熱反応で発生した熱量を温度補償に利用でき、加熱機構を備えていない二次精錬装置を使用した場合でも出鋼温度を過度に高くする必要がなくなる。
【図面の簡単な説明】
【図１】溶鋼のＡｌ濃度と自由酸素との平衡関係に及ぼす温度の影響
【図２】表面疵の発生に及ぼすＡｌ濃度の影響
【図３】本発明法と従来法とで比較した介在物レベル
【図４】本発明法と従来法とで比較した表面品質レベル
【図５】本発明法と従来法とで比較したＲＨ浸漬管の寿命
【図６】本発明法と従来法とで比較した出鋼温度[0001]
[Industrial applications]
The present invention relates to a method for melting high-purity high-Ni steel by secondary refining by deoxidation of Al and Si.
[0002]
[Prior art]
As a material used as a material for a shadow mask, a lead frame material, a magnetic material, a sealing alloy, a structure for low temperature, etc. by utilizing low thermal expansion characteristics, magnetic characteristics, etc., for example, a Ni content of 30 to 50% by weight. High-purity Ni steels and Fe-Ni alloys (hereinafter collectively referred to as high-purity Ni steels) are manufactured. When producing high-purity high-Ni steel on an industrial scale, impurities inevitably mix in addition to the main components of Fe and Ni. In some cases, alloying elements are intentionally added, but elements other than alloying elements having specified values for special reasons, such as C, Si, P, S, Al, O, and N, are generally impurities. In high purity Ni steel or Fe-Ni alloy.
When the impurity content is large, various adverse effects are caused. For example, in the shadow mask material, the thermal expansion coefficient increases due to the increase in the impurity content, and the etching property also decreases. As a result, the original material characteristics of the high-purity high-Ni steel cannot be sufficiently exhibited. In addition, even during the production of steel, the hot workability is reduced, the yield is reduced, and the production cost is increased. Therefore, it is required to minimize the content of impurities when melting high-purity high-Ni steel.
[0003]
Above all, since extremely low C is required, a method of removing C in the molten metal as CO gas by a reaction of C + O → CO in secondary refining using a vacuum degassing facility such as an RH apparatus has been adopted. In this refining reaction, since a certain amount or more of dissolved oxygen is required in the molten metal, oxygen is added as necessary. As a result, in order to reduce the dissolved oxygen to the order of ppm after the decarburization refining, a deoxidation treatment is performed by adding Al, Fe-Si or the like.
When the high-purity high-Ni steel is deoxidized with Al, the deoxidized product, Al ₂ O _3, is adsorbed on the ladle slag during the secondary refining and does not remain in the molten metal. However, Al that has not been consumed in deoxidation remains in the molten metal, reacts with oxygen in the air during movement to the casting process or during casting, and is reoxidized to produce Al ₂ O ₃ again. As a result, Al ₂ O ₃ -based inclusions remain on the obtained slabs and the like, which causes flaws on the product surface.
Deoxidation using a Si additive such as Fe-Si is adopted in order to avoid adverse effects caused by Al ₂ O ₃ -based inclusions. In the Si deoxidation, the deoxidation reaction proceeds to a certain level, but the deoxidation does not proceed further unless the deoxidized product SiO ₂ floats. In order to promote the floating of SiO ₂ , it is required to reduce the SiO ₂ activity of the ladle slag. Therefore, by adding a slag component modifier such as CaO or CaF ₂ to molten steel to reduce the SiO ₂ activity of the ladle slag, deoxidation proceeds to about 10 ppm for the first time.
[0004]
[Problems to be solved by the invention]
In the Si deoxidation, it is necessary to add a large amount of a slag regulator such as CaO and CaF ₂ in order to reduce the SiO ₂ activity of the ladle slag. Excessive addition of CaF ₂ or the like lowers the melting point of the ladle slag, abnormally damages the refractory, and shortens the life of the ladle furnace wall and the dip tube.
Further, since an exothermic reaction cannot be used as in the case of Al addition, temperature compensation cannot be performed in a secondary refining device not provided with an arc heating device, so that the tapping temperature has to be raised more than necessary. As a result, the yield of the main raw material and the auxiliary raw material is reduced, the life of the refractory is shortened, and the power consumption and the unit temperature of the heating agent are increased.
The present invention has been devised to solve such a problem, and by reducing the free oxygen in the molten metal by adding Al prior to Si deoxidation, the amount of SiO ₂ generated during Si deoxidation can be reduced. An object of the present invention is to produce a high-purity high-Ni steel without reducing the tapping temperature by setting the tapping temperature excessively high by utilizing the heat generated by oxidation of Al while reducing the amount of addition of the slag regulator.
[0005]
[Means for Solving the Problems]
In order to achieve the object, the deoxidation method of the present invention is applied to a method of producing a high-purity high-Ni molten steel having a C concentration of 0.01% by weight or less in a secondary refining device not equipped with an arc heating device. In this method, Al is added so that the free oxygen concentration of the molten steel remains at 0.02% by weight or more, and then a Si additive is added to deoxidize Si. The addition of Al is performed once or separately.
The secondary refining device used in the present invention includes an RH vacuum degassing device, a DH vacuum degassing device, a VOD vacuum degassing device, and the like.
[0006]
[Action]
In the deoxidation method according to the present invention, the initial deoxidation in which Al is added prior to the Si deoxidation is performed to reduce the free oxygen concentration of the molten steel. This reduces the free oxygen concentration during Si deoxidation and reduces the amount of SiO ₂ generated. Therefore, the amount of the slag adjuster added decreases. In addition, since the amount of heat generated by the exothermic reaction between oxygen in molten steel and Al can be used to raise the temperature of molten steel, it is not necessary to excessively raise the tapping temperature.
FIG. 1 shows the effect of temperature on the equilibrium relationship between Al and free oxygen. From FIG. 1, when the free oxygen is 0.02% by weight or more at a temperature of 1650 ° C. or lower during general secondary refining during melting of high purity and high Ni steel, the equilibrium Al concentration is 0.0015% by weight or less. It turns out that it becomes. From the results of various experiments by the present inventors, as shown in FIG. 2, when the Al concentration of the molten steel becomes 0.002% by weight or less, re-oxidation of Al during the transfer to the casting process or during casting. It has been found that the generated Al ₂ O ₃ -based inclusions do not cause surface defects in the product.
[0007]
【Example】
Pretreatment of hot metal used for the production of ordinary steel and special steel, using a converter by the LD-RH method and RH vacuum degassing equipment, and using various high-pressure steels with Ni contents in the range of 30 to 50% by weight. High purity Ni steel was manufactured. A typical operation example will be described below. The target component values of the high-purity high-Ni steel are as follows: C: 0.01% by weight or less, Si: 0.05% by weight or less, Ni: 35.5 to 36.5% by weight, P: 0.005% by weight or less, S: 0.003 wt% or less, Al: 0.01 wt% or less, O: 50 ppm or less, N: 30 ppm or less, and 36% Ni steel with other impurity components reduced as much as possible.
68 tons of blast furnace hot metal was de-Si treated with a gutter and transferred to a pretreatment facility. In a pretreatment facility, 19 kg / ton of soda ash, 56 kg / ton of a CaO-based dephosphorizing agent, and 6.5 Nm ³ / ton of oxygen were respectively injected to remove S / P.
[0008]
The pretreated hot metal is charged into a converter, and further 31 tons of pure Ni, 400 kg of Fe-Si as a deoxidizing agent, 2800 kg of CaO as a slag-making agent, a basicity adjusting and deoxidizing agent, and 980 kg of light-burning dolomite as an additive for furnace wall protection. 460 kg of CaF ₂ as a slag viscosity modifier and 11500 kg of carbon briquettes as a temperature raising agent were charged. After charging, oxygen blowing was performed, and decarburization, Ni dissolution, Si removal, P removal and N removal were performed.
As a result of analysis after the end of the blowing, the contents of P, S, Ni and N were all within the range of the target component values, and the molten steel temperature had risen to 1700 ° C. The molten steel was tapped into a ladle. In the tapping stage, 300 kg of CaO as a slag-making agent was charged in the ladle in advance, and slag was cut so that the converter slag did not flow into the ladle.
The obtained high Ni molten steel was transferred to an RH vacuum degassing facility, and vacuum decarburized. Then, when the molten steel temperature was measured, it was 20 ° C. lower than the target value. Therefore, 25 Nm ³ of oxygen was blown into the molten steel, and 55 kg of Al was added to raise the temperature of the molten steel. When the free oxygen of the molten metal after the temperature rise was measured by a rapid analyzer, it was 0.025% by weight. Next, component adjustment and vacuum degassing were performed.
[0009]
When the free oxygen after component adjustment and vacuum degassing was measured and found to be 0.02% by weight, 100 kg of Fe-Si was added, and the molten steel was refluxed for 2 minutes. When the molten steel after the reflux was sampled and the Si concentration was measured, the Si concentration was 0.05% by weight, which was within the standard range. Therefore, 300 kg of CaO and 200 kg of CaF ₂ were promptly added to the RH vacuum chamber to produce slag for deoxidation. Thereafter, the molten steel was refluxed again for 10 minutes, and deoxidized with a ladle slag. At the time of RH serving, free oxygen was 0.001% by weight and Al concentration was 0.001% by weight.
Table 1 shows the molten steel component value, molten steel temperature, molten steel weight, and slag composition in each of the above steps.
[0010]

[0011]
As shown in Table 1, each component of the molten steel after the RH vacuum degassing treatment reached the target value, and the molten steel temperature was also appropriate. Therefore, this molten steel was cast in a continuous casting process to obtain a high-purity high-Ni steel material having a predetermined size and shape. As a result of examining the quality of the obtained continuous cast slab, as shown in FIGS. 3 and 4, both the inclusion level and the surface quality level exhibited almost the same properties as the slab manufactured by the conventional method.
In another test, Al was added twice, three times, or more times to adjust the temperature during the treatment. In each case, 0.020% by weight or more of free oxygen was left. Therefore, the Al concentration was 0.002% by weight or less at the time of RH dispensing, and there was no problem with inclusions and the surface quality level.
Further, since Fe-Si was charged into the molten steel in which the free oxygen concentration was lowered by adding Al, the amount of SiO ₂ generated due to the deoxidation of Si was reduced. Therefore, the addition amount of the ladle slag adjuster could be reduced, and as shown in FIG. 5, the life of the RH immersion tube could be approximately doubled compared to the conventional method. Further, since the temperature of the molten steel is increased by the addition of Al, the tapping temperature of the converter or the electric furnace can be reduced by about 20 ° C. as shown in FIG. Therefore, it was found that high-purity high-Ni steel can be manufactured at low cost.
[0012]
【The invention's effect】
As described above, in the present invention, prior to the Si deoxidation, the free oxygen concentration of the molten steel is reduced by adding Al, and then the Si is deoxidized using Fe-Si or the like. Therefore, the amount of SiO ₂ generated during the deoxidation of Si is reduced, and the amount of the slag modifier added can be reduced accordingly. Reduced. Further, the heat generated by the oxidation exothermic reaction of Al can be used for temperature compensation, and even when a secondary refining device not provided with a heating mechanism is used, it is not necessary to excessively increase the tapping temperature.
[Brief description of the drawings]
FIG. 1 shows the effect of temperature on the equilibrium relationship between Al concentration and free oxygen in molten steel. FIG. 2 shows the effect of Al concentration on the occurrence of surface flaws. FIG. 3 Inclusions compared between the method of the present invention and the conventional method. Level [Figure 4] Surface quality level compared between the method of the present invention and the conventional method [Fig. 5] Life of RH immersion tube compared between the method of the present invention and the conventional method [Figure 6] Comparison between the method of the present invention and the conventional method Tapping temperature

Claims

When producing a high-purity high-Ni molten steel having a C concentration of 0.01% by weight or less using a secondary refining apparatus without an arc heating device, the free oxygen concentration of the molten steel remains at 0.02% by weight or more after Al deoxidation. A method for producing a high-purity high-Ni molten steel characterized by adding Al and then adding a Si additive to deoxidize Si.

2. The method for producing a high-purity high-Ni molten steel according to claim 1, wherein Al is added once or in a plurality of times.