JP7311785B2 - Melting method of Al-deoxidized steel - Google Patents
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Description
本発明は、粗大なアルミナクラスタの形成を抑制するために用いて好適なＡｌ脱酸鋼の溶製方法に関する。 TECHNICAL FIELD The present invention relates to a method for melting Al-deoxidized steel suitable for suppressing the formation of coarse alumina clusters.
Ａｌは強力な脱酸剤であり、瞬時に溶存酸素を低減でき、効果も安定していることから、製鋼プロセスの中で多用されている。しかしながら、溶存酸素とＡｌが反応した場合、生成したアルミナが樹枝状に連なった、いわゆるアルミナクラスタが生成してしまう。鋼材中にアルミナクラスタが含まれている場合、鋳造性を悪化させることに加え、製品まで残存した場合、破壊や疵の起点になるなど、製品性能を著しく低下させてしまう。 Al is a strong deoxidizing agent, can instantly reduce dissolved oxygen, and has a stable effect, so it is often used in the steelmaking process. However, when dissolved oxygen reacts with Al, so-called alumina clusters, in which the formed alumina is linked in a dendritic form, are formed. When alumina clusters are contained in the steel material, in addition to deteriorating the castability, if they remain in the product, they become the starting points of fractures and flaws, resulting in a significant deterioration in product performance.
例えば、最も清浄性を要求される軸受鋼といった清浄鋼では、鋼材中のアルミナクラスタが破壊の起点となり、転動疲労寿命を低下させることが知られている。また、大型構造物として用いられる厚板鋼においては、アルミナクラスタが溶接時の靱性を低下させる場合がある。さらに、自動車用鋼板等に使用される薄板鋼では、アルミナクラスタがスラブの表層欠陥であるふくれ疵の要因となり、鋼板表面の美麗さを損なう場合もある。 For example, in clean steel such as bearing steel, which requires the highest degree of cleanliness, alumina clusters in the steel material are known to initiate fracture and reduce the rolling contact fatigue life. In addition, alumina clusters may reduce toughness during welding in plate steel used for large structures. Furthermore, in thin steel sheets used for steel sheets for automobiles and the like, alumina clusters may cause blistering defects, which are surface layer defects of the slab, and may impair the beauty of the steel sheet surface.
このように、Ａｌなどの強脱酸元素を溶鋼に添加することによってアルミナクラスタが生成し、製品段階の性能を低下させる要因になりうる。また、アルミナの生成を抑制するために他の酸化物を生成させた場合には、酸化物の種類によってはノズル詰まりの要因となることから、生産性が低下する場合もある。そこで、溶鋼段階でアルミナなどの非金属介在物を低減する技術が提案されている。 As described above, the addition of a strong deoxidizing element such as Al to molten steel generates alumina clusters, which can be a factor in deteriorating the performance of the product. Further, when other oxides are generated to suppress the generation of alumina, depending on the type of oxides, they may cause nozzle clogging, which may reduce productivity. Therefore, techniques for reducing non-metallic inclusions such as alumina at the molten steel stage have been proposed.
例えば特許文献１には、真空脱ガス装置にて溶鋼を撹拌して非金属介在物を浮上・分離させる高清浄度鋼の溶製方法が開示されている。この手法は生成した非金属介在物を物理的に溶鋼から除去する技術であり、効率良く凝集させて見かけの介在物径を大きくして除去速度を増大させ、かつ、長時間処理することで鋼の清浄性を向上させるものである。しかしながら、この方法は長時間処理を行うことから生産性が低く、かつＡｌ脱酸鋼を溶製する場合にはＡｌの添加は必須となり、その場合にはアルミナクラスタの生成を抑制することができない。 For example, Patent Literature 1 discloses a high-cleanliness steel melting method in which molten steel is stirred in a vacuum degassing device to float and separate non-metallic inclusions. This technique is a technique to physically remove the generated non-metallic inclusions from molten steel. It improves the cleanliness of the However, this method has low productivity because it takes a long time to process, and the addition of Al is essential when melting Al-deoxidized steel, and in that case, the formation of alumina clusters cannot be suppressed. .
また、特許文献２には、転炉から溶鋼を末脱酸出鋼し、溶鋼中酸素濃度が１００ｐｐｍ以下になるまで炭素含有物を溶鋼に添加し、その後Ａｌを添加する高清浄鋼の溶製方法が開示されている。この手法は、炭素含有物を添加することで溶鋼中の酸素をＣＯガスとして除去し、清浄性を高めているが、この技術を用いてもＡｌを添加することによってアルミナが生成され、不可避的にアルミナクラスタが形成されてしまう。 Further, in Patent Document 2, molten steel is deoxidized from a converter, carbon-containing substances are added to the molten steel until the oxygen concentration in the molten steel is 100 ppm or less, and then Al is added to produce highly clean steel. A method is disclosed. This method removes oxygen in the molten steel as CO gas by adding carbon-containing substances to improve cleanliness. Alumina clusters are formed in the
さらに特許文献３には、Ａｌ濃度とＣ濃度とを所定の濃度に調整した状態で、環流型脱ガス装置において１０分以上減圧下で環流処理を行い、環流後にＺｒ，ＲＥＭを添加する技術が開示されている。しかしながら技術はＡｌを添加することができないため、Ａｌ脱酸鋼を溶製することができない。 Furthermore, Patent Document 3 discloses a technique of performing reflux treatment under reduced pressure for 10 minutes or more in a reflux degassing device in a state where the Al concentration and C concentration are adjusted to predetermined concentrations, and adding Zr and REM after reflux. disclosed. However, since the technology cannot add Al, Al-deoxidized steel cannot be melted.
以上のようにＡｌ脱酸鋼を溶製する場合には、Ａｌを添加して脱酸を行うため、不可避的にアルミナクラスタが形成してしまう。また、アルミナの生成を抑制しようとすると、操業時間が著しく長くなったり、他の酸化物によって鋳造時などにノズルの閉塞が生じやすくなったり、操業に支障をきたす場合がある。 As described above, when Al-deoxidized steel is melted, Al is added for deoxidation, so alumina clusters are inevitably formed. In addition, if an attempt is made to suppress the formation of alumina, the operation time may be significantly lengthened, and other oxides may easily cause clogging of the nozzle during casting, thereby interfering with the operation.
本発明は前述の問題点を鑑み、操業上の支障が生じないようにして、アルミナクラスタの形成を抑制可能なＡｌ脱酸鋼の溶製方法を提供することを目的とする。 SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a smelting method for Al-deoxidized steel capable of suppressing the formation of alumina clusters without impeding the operation.
本発明は以下の通りである。
（１）
真空脱ガス装置を用いて、ｓｏｌ．Ａｌ濃度が０．００５０質量％以下の溶鋼を環流させて脱炭処理を行い、溶鋼中のＴ．Ｏ濃度を０．００３０質量％以下まで低下させ、その後、以下の（１）式の範囲でＲＥＭを前記溶鋼に添加して、ＲＥＭの添加完了から１．５～３分の間にＡｌを添加することを特徴とするＡｌ脱酸鋼の溶製方法。
６１．２×％Ｔ．Ｏ≦Ｗ＿ＲＥＭ ・・・（１）
ここで、Ｗ＿ＲＥＭはＲＥＭ添加量（ｋｇ／ｔｏｎ）を表し、％Ｔ．Ｏは、ＲＥＭを添加する前の溶鋼中の全Ｏ濃度（質量％）を表す。
The present invention is as follows.
(1)
Using a vacuum degasser, sol. Molten steel having an Al concentration of 0.0050% by mass or less is circulated for decarburization, and the T.E. Reduce the O concentration to 0.0030% by mass or less, then add REM to the molten steel within the range of the following formula (1), and add Al within 1.5 to 3 minutes after the completion of REM addition. A melting method for Al-deoxidized steel, characterized by:
61.2 x %T. O≦W_REM (1)
Here, W_REM represents the amount of REM added (kg/ton), %T. O represents the total O concentration (mass%) in the molten steel before adding REM.
本発明によれば、操業上の支障が生じないようにして、アルミナクラスタの形成を抑制可能なＡｌ脱酸鋼の溶製方法を提供することができる。 According to the present invention, it is possible to provide a method for melting Al-deoxidized steel that can suppress the formation of alumina clusters without causing operational problems.
以下、本発明の実施形態について詳細に説明する。なお、以下の説明で「％」とは特段の説明がない限り、質量％を指すものとする。 BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. In the following description, "%" refers to % by mass unless otherwise specified.
製品性能を著しく低下させるアルミナクラスタの生成要因としては、アルミナとアルミナの境界に生じている液体酸化鉄（ＦｅＯ）の存在が報告されている（非特許文献１参照）。この液体酸化鉄は、単体のアルミナが生成している状況、すなわち溶鋼中のＡｌ濃度が高い場合であっても生成していることから、Ａｌ脱酸の範囲では液体酸化鉄の生成を抑制するのは困難である。液体酸化鉄の生成を抑制するには、Ａｌよりも脱酸力が強いＲＥＭを添加して液体酸化鉄を還元するのが効果的であると考えられる。ここでＲＥＭ（Rare Earth Metal）とは、周期表の３族に属するＳｃ，Ｙ，ランタノイド（Ｌａ，Ｃｅ等、原子番号５７～７１の１５元素）から選ばれた１種以上の希土類元素を意味し、特に、Ｃｅ，Ｌａ，ＰｒまたはＮｄのうちの１種以上の元素が該当する。 The presence of liquid iron oxide (FeO) generated at the boundary between alumina has been reported as a factor for the formation of alumina clusters that significantly degrade product performance (see Non-Patent Document 1). This liquid iron oxide is generated even in a situation where simple alumina is generated, that is, even when the Al concentration in the molten steel is high, so the generation of liquid iron oxide is suppressed within the range of Al deoxidization. is difficult. In order to suppress the formation of liquid iron oxide, it is considered effective to add REM, which has stronger deoxidizing power than Al, to reduce the liquid iron oxide. Here, REM (Rare Earth Metal) means one or more rare earth elements selected from Sc, Y, and lanthanoids (La, Ce, etc., 15 elements with atomic numbers of 57 to 71) belonging to Group 3 of the periodic table. and in particular one or more of the elements Ce, La, Pr or Nd.
しかしながら、Ａｌ脱酸した後にＲＥＭを添加したとしても、アルミナとアルミナの結合部分に存在する液体酸化鉄は、アルミナ自身が盾となっているため、脱酸力が強い元素を添加しても処理時間内には還元しきれない可能性がある。一方で、Ａｌ脱酸していない未脱酸もしくは弱脱酸状況での溶鋼中Ｏ濃度は数１０ｐｐｍから数１００ｐｐｍ程度であり、この酸素を全てＲＥＭで脱酸するには多量のＲＥＭが必要であり、工業的に成立しない。ここで、溶鋼中Ｏ濃度は、溶存酸素と酸化物中の酸素とを合わせた全Ｏ濃度であり、以下、Ｔ．Ｏ濃度と記載する場合がある。 However, even if REM is added after Al deoxidization, the liquid iron oxide present in the bonding portion between alumina and alumina is shielded by alumina itself. It may not be possible to return it in time. On the other hand, the O concentration in the molten steel in an undeoxidized or weakly deoxidized state without Al deoxidization is about several 10 ppm to several 100 ppm, and a large amount of REM is required to deoxidize all this oxygen with REM. Yes, it is not industrially viable. Here, the O concentration in the molten steel is the total O concentration including the dissolved oxygen and the oxygen in the oxide. It may be described as O concentration.
そこで本発明者らは、予め溶存酸素をＣで脱酸した後にＲＥＭを添加すれば、少ないＲＥＭ添加量で脱酸できることに着想した。但し、溶鋼は取鍋上のスラグもしくは僅かながら大気によって再酸化されるため、ＲＥＭを添加してからある程度時間が経過してしまうと、ＲＥＭから溶存酸素が移行し、液体酸化鉄が生成されやすくなってしまう。そこで本発明者らはさらに、ＲＥＭを添加した後に、所定の時間内にＡｌを添加すれば、液体酸化鉄が生じず、アルミナクラスタの生成が抑制できることに着想した。 Therefore, the present inventors came up with the idea that if REM is added after deoxidizing dissolved oxygen with C in advance, deoxidation can be achieved with a small amount of REM added. However, since the molten steel is re-oxidized by the slag on the ladle or slightly by the air, if a certain amount of time has passed since REM was added, dissolved oxygen will migrate from REM, and liquid iron oxide will easily be generated. turn into. Therefore, the present inventors further came up with the idea that if Al is added within a predetermined period of time after the addition of REM, liquid iron oxide will not occur and the formation of alumina clusters can be suppressed.
本発明者らは、以上のような着想に基づいて液体酸化鉄の生成を抑制することによって、アルミナクラスタの生成を抑制するための諸条件を調査し、本発明を完成するに至った。以下、アルミナクラスタの生成を抑制するための詳細な条件について説明する。 Based on the idea as described above, the present inventors investigated various conditions for suppressing the formation of alumina clusters by suppressing the formation of liquid iron oxide, and completed the present invention. Detailed conditions for suppressing the formation of alumina clusters will be described below.
［脱炭処理前の条件］
製鋼炉から取鍋に溶鋼が出鋼された後、真空脱ガス装置まで搬送される。なお、取鍋に溶鋼が出鋼された後、真空脱ガス装置まで搬送される間に、合金等を添加して成分調整してもよい。
[Conditions before decarburization treatment]
After the molten steel is tapped from the steelmaking furnace into the ladle, it is conveyed to the vacuum degassing device. After the molten steel is tapped into the ladle, the composition may be adjusted by adding an alloy or the like while it is conveyed to the vacuum degassing device.
本実施形態では、製鋼炉から出鋼された溶鋼に対して、真空脱ガス装置を用いて減圧し、溶鋼中のＣとＯを反応させて脱炭処理を行うことにより溶存酸素濃度を低減させる。ここで真空脱ガス装置とは、真空槽を要する溶鋼処理装置であって、代表的な装置としてＲＨ型真空脱ガス装置がある。ＲＨ型真空脱ガス装置では、取鍋中の溶鋼に浸漬管を浸漬させて真空槽内の圧力を低下させることで溶鋼を真空槽に吸い上げ、さらに溶鋼中に環流ガスを流すことで、溶鋼を取鍋と真空槽内とで環流させる。環流中の溶鋼では、溶鋼が減圧雰囲気にさらされることから脱ガス反応が促進されるとともに、介在物の凝集、浮上除去が促進される。 In this embodiment, molten steel tapped from a steelmaking furnace is depressurized using a vacuum degassing device, and C and O in the molten steel are reacted to perform decarburization, thereby reducing the concentration of dissolved oxygen. . Here, the vacuum degassing apparatus is a molten steel processing apparatus that requires a vacuum chamber, and a representative apparatus is an RH type vacuum degassing apparatus. In the RH-type vacuum degassing equipment, the molten steel is sucked into the vacuum chamber by immersing an immersion tube in the molten steel in the ladle to reduce the pressure in the vacuum chamber, and by flowing a reflux gas through the molten steel, the molten steel is removed. Circulate between the ladle and the vacuum chamber. In the molten steel being circulated, the molten steel is exposed to a reduced-pressure atmosphere, which promotes the degassing reaction, as well as the agglomeration and floatation removal of inclusions.
なお、真空脱ガス装置で脱炭処理を行う前に、ＳｉなどのＡｌ以外の脱酸剤を添加して脱酸し、脱炭処理の負荷を低減してもよい。また、脱炭処理では、ＣとＯとの反応でＣＯ気泡が溶鋼中に生じるが、ＣＯ気泡は介在物等を核にした方がエネルギー的に有利であることから、脱炭反応を用いることで介在物中の酸素除去も効率良く進む。 Before performing the decarburization treatment with the vacuum degassing device, a deoxidizing agent other than Al such as Si may be added for deoxidation to reduce the load of the decarburization treatment. In addition, in the decarburization process, CO bubbles are generated in the molten steel due to the reaction between C and O. Since it is more advantageous in terms of energy to use inclusions as nuclei for the CO bubbles, decarburization reaction should be used. Oxygen removal from inclusions also proceeds efficiently.
また、真空脱ガス装置で脱炭処理する前の段階で溶鋼中のｓｏｌ．Ａｌ濃度が０．００５％を超えていると、溶鋼中にアルミナが生成してアルミナクラスタを形成し、アルミナクラスタが懸濁する状態となる。一度アルミナクラスタが形成されてしまうと、アルミナ同士の接合を外すには多量の強脱酸元素が必要である。また、一度懸濁したアルミナクラスタを溶鋼から取り除くには長時間の環流処理が必要となる。このため、脱炭処理前のｓｏｌ．Ａｌ濃度は０．００５％以下とする。なお、通常の操業で溶鋼を溶製する場合には、Ａｌを添加しない限り、ｓｏｌ．Ａｌ濃度は０．００５％以下となる。また、ｓｏｌ．Ａｌ濃度は低位であるほうがアルミナ生成量は低減できるが、溶鋼中からｓｏｌ．Ａｌを完全に低減することは困難である。好ましくは、脱炭処理前のｓｏｌ．Ａｌ濃度は、０．０００５～０．００２０％である。 In addition, the sol. When the Al concentration exceeds 0.005%, alumina is generated in the molten steel to form alumina clusters, and the alumina clusters become suspended. Once alumina clusters are formed, a large amount of a strong deoxidizing element is required to break the bond between the aluminas. In addition, a long period of reflux treatment is required to remove once-suspended alumina clusters from the molten steel. Therefore, the sol. The Al concentration is set to 0.005% or less. In addition, when melting molten steel in a normal operation, unless Al is added, sol. Al concentration becomes 0.005% or less. Also, sol. Although the amount of alumina produced can be reduced when the Al concentration is low, sol. It is difficult to completely reduce Al. Preferably, the sol. The Al concentration is 0.0005-0.0020%.
［脱炭処理後（ＲＥＭ添加前）の全Ｏ濃度：０．００３０％以下］
Ｏは鋼材の製造過程において不可避的に含有される元素であり、溶存酸素、もしくは酸化物として溶鋼中に存在する。このため、ＲＥＭを残存させるためには、溶存酸素に加え、酸化物中の酸素も考慮することが必要である。ＲＥＭは脱酸力が強く、溶存酸素と反応することに加え、多くの酸化物を還元し、自らはＲＥＭ酸化物となる。ＲＥＭ添加前の全Ｏ濃度（Ｔ．Ｏ濃度）が高い場合、脱酸に要するＲＥＭ添加量が多くなり、溶製コストが高くなってしまう。また、ＲＥＭ酸化物が過剰に生成すると、アルミナクラスタの生成は抑制されるが、ＲＥＭ酸化物に起因して鋳造時にノズル閉塞を生じさせてしまう。このため、真空脱ガス装置を用いて脱炭処理によりＣとＯとを反応させ、ＲＥＭ添加前のＯ濃度を０．００３０％以下に制御しておくことが必要である。
[Total O concentration after decarburization treatment (before REM addition): 0.0030% or less]
O is an element that is inevitably contained in the manufacturing process of steel materials, and is present in molten steel as dissolved oxygen or oxides. Therefore, in order to allow REM to remain, it is necessary to consider not only dissolved oxygen but also oxygen in the oxide. REM has a strong deoxidizing power, and in addition to reacting with dissolved oxygen, it reduces many oxides, and itself becomes REM oxide. When the total O concentration (T.O concentration) before REM addition is high, the REM addition amount required for deoxidation increases, resulting in an increase in smelting cost. Also, if REM oxides are excessively produced, the formation of alumina clusters is suppressed, but the REM oxides cause nozzle clogging during casting. Therefore, it is necessary to react C and O by decarburization using a vacuum degassing device, and control the O concentration to 0.0030% or less before adding REM.
［ＲＥＭ添加量］
ＲＥＭは強脱酸元素であり、一般的には鋼材の組織を微細化するといった用途で添加される。本実施形態においては、アルミナクラスタの生成要因の一つと考えられる液体酸化鉄の生成を抑制するためにＲＥＭが添加される。以下の（１）式を満たす量のＲＥＭを添加すれば、ＲＥＭ酸化物が生成し、Ａｌ添加前において液体酸化鉄が生成しない状態とすることが可能である。なお、ＲＥＭを添加した場合、ＲＥＭ硫化物を生成する可能性があるが、通常の操業で溶鋼に含まれるＳ濃度では、添加したＲＥＭのほとんどはＲＥＭ酸化物となり、ＲＥＭ硫化物はほとんど生成されないため、無視してよい。
６１．２×％Ｔ．Ｏ≦Ｗ＿ＲＥＭ ・・・（１）
ここで、％Ｔ．ＯはＲＥＭ添加前の溶鋼中の全Ｏ濃度（質量％）を表し、Ｗ＿ＲＥＭはＲＥＭの添加量（ｋｇ／ｔｏｎ）を表す。
[REM addition amount]
REM is a strong deoxidizing element and is generally added for purposes such as refining the structure of steel materials. In this embodiment, REM is added in order to suppress the formation of liquid iron oxide, which is considered to be one of the factors for the formation of alumina clusters. If REM is added in an amount that satisfies the following formula (1), REM oxide is generated, and it is possible to create a state in which liquid iron oxide is not generated before Al is added. When REM is added, REM sulfide may be generated, but at the S concentration contained in molten steel in normal operation, most of the added REM becomes REM oxide, and almost no REM sulfide is generated. can therefore be ignored.
61.2 x %T. O≦W_REM (1)
where %T. O represents the total O concentration (% by mass) in the molten steel before REM addition, and W_REM represents the amount of REM added (kg/ton).
ここで、ＲＥＭとしてＣｅ（原子量：１４０．１ｇ／ｍｏｌ）を仮定すると、溶鋼中の酸素（原子量：１６ｇ／ｍｏｌ）をＣｅ2Ｏ3として固定するために必要な化学量論的なＣｅ重量は、酸素濃度の５．８４倍（＝（１４０．１＊２）／（１６＊３））となる。単位を質量％からｋｇ／ｔｏｎに変換すると、理論上、溶鋼中の酸素をＲＥＭ酸化物として固定するのに｛％Ｔ．Ｏ×５８．４｝ｋｇ／ｔｏｎ以上が必要となるが、実際には添加時の合金歩留りや環流中の濃度低下が生じる。これらを勘案し、小型実験や実機試験結果から実験的に検討した結果、ＲＥＭ添加量Ｗ＿ＲＥＭは（１）式の範囲とする必要があることが確認できた。 Here, assuming Ce (atomic weight: 140.1 g/mol) as REM, the stoichiometric Ce weight required to fix oxygen (atomic weight: 16 g/mol) in molten steel as Ce 2 O 3 is , 5.84 times the oxygen concentration (=(140.1*2)/(16*3)). When the units are converted from % by mass to kg/ton, theoretically {%T. Ox 58.4} kg/ton or more is required, but actually, the yield of the alloy at the time of addition and the concentration during recirculation decrease. As a result of taking these into consideration and experimentally examining the results of small-scale experiments and actual machine tests, it was confirmed that the REM addition amount W_REM should be within the range of formula (1).
以上のように、ＲＥＭ添加量Ｗ＿ＲＥＭが６１．２×％Ｔ．Ｏよりも少ないと、溶鋼中にＲＥＭ酸化物が十分に生成されないため、液体酸化鉄が生成してしまいその後のＡｌ添加によりアルミナクラスタが生成してしまう。このため、ＲＥＭ添加量は（１）式の範囲を満たしていることが必要である。ＲＥＭ添加量Ｗ＿ＲＥＭの上限は特に規定しないが、ＲＥＭ添加量が多すぎると液体酸化物の生成抑制効果が得られる一方でその効果が飽和し、合金コストが増大してしまう。このため、ＲＥＭ添加量Ｗ＿ＲＥＭは以下の（２）式を満たす範囲とすることが好ましい。
Ｗ＿ＲＥＭ≦６４．２×％Ｔ．Ｏ ・・・（２）
As described above, when the REM addition amount W_REM is 61.2×%T. If the amount is less than O, REM oxides are not sufficiently generated in the molten steel, so that liquid iron oxide is generated and alumina clusters are generated by the subsequent addition of Al. Therefore, it is necessary that the amount of REM added satisfies the range of formula (1). Although the upper limit of the REM addition amount W_REM is not particularly defined, if the REM addition amount is too large, while the effect of suppressing the generation of liquid oxide can be obtained, the effect is saturated and the alloy cost increases. Therefore, it is preferable that the REM addition amount W_REM is set in a range that satisfies the following formula (2).
W_REM≦64.2×%T. O (2)
また、ＲＥＭの添加手法としては、金属単体で添加してもよく、複数種類の金属（ＲＥＭ）が混入しているいわゆるミッシュミタルの形状で添加してもよい。また、ＦｅやＳｉといったＲＥＭ以外の他の金属との合金として添加してもよい。その場合は、合金中のＲＥＭの含有率を乗じて、ＲＥＭ相当量が（１）式を満たす範囲にあればよい。 Moreover, as a method for adding REM, it may be added in the form of a single metal, or may be added in the form of so-called mischmittal in which a plurality of types of metals (REM) are mixed. Also, it may be added as an alloy with other metals other than REM, such as Fe and Si. In that case, the content of REM in the alloy should be multiplied so that the REM equivalent content satisfies the formula (1).
［ＲＥＭ添加後のＡｌ添加］
その後、溶鋼中にＲＥＭが微量濃度残存している間、具体的にはＲＥＭ添加完了から３分以内にＡｌを添加する。ＲＥＭの添加後３分超経過してからＡｌを添加すると、ＲＥＭによる脱酸効果が低下した状態、つまり液体酸化鉄の生成を抑制できない状態でＡｌを添加することになり、アルミナクラスタが生成されやすくなる。したがって、ＲＥＭ添加後３分以内にＡｌを添加する必要がある。
[Addition of Al after addition of REM]
Thereafter, while REM remains in the molten steel at a trace concentration, specifically within 3 minutes after the completion of REM addition, Al is added. If Al is added more than 3 minutes after the addition of REM, Al is added in a state where the deoxidizing effect of REM is reduced, that is, in a state where the formation of liquid iron oxide cannot be suppressed, and alumina clusters are formed. easier. Therefore, it is necessary to add Al within 3 minutes after adding REM.
一方、ＲＥＭを添加して１．５分経たないうちにＡｌを添加すると、溶鋼中にＲＥＭが均一に混合されていない状況でＡｌが添加されるため、ＲＥＭ濃度が低いところでアルミナクラスタが生成してしまう。このため、ＲＥＭ添加完了から１．５～３分の間にＡ１を添加する必要がある。 On the other hand, if Al is added within 1.5 minutes after REM is added, Al is added in a state in which REM is not uniformly mixed in the molten steel, so alumina clusters are formed where the REM concentration is low. end up Therefore, it is necessary to add A1 within 1.5 to 3 minutes after the completion of REM addition.
なお、Ａｌの添加量は、Ａｌ脱酸鋼を溶製するのに必要な量とする。アルミナとアルミナの境界に生じている液体酸化鉄（ＦｅＯ）を生じさせない分量のＡｌを添加する必要があるが、Ａｌ脱酸鋼では、さらにＡｌＮのピン止め効果を利用したオーステナイト粒度制御に必要な分量のＡｌが必要である。具体的には、Ａｌを添加することによって溶鋼中のｓｏｌ．Ａｌ濃度は０．０２～０．１０％とすることが好ましく、０．０３～０．０８％とすることがさらに好ましい。Ａｌ添加後は、溶鋼を必要な成分および温度に調整する。 Note that the amount of Al to be added is the amount necessary to melt the Al-deoxidized steel. It is necessary to add Al in an amount that does not cause liquid iron oxide (FeO) occurring at the boundary between alumina and alumina. A certain amount of Al is required. Specifically, by adding Al, the sol. The Al concentration is preferably 0.02-0.10%, more preferably 0.03-0.08%. After adding Al, the molten steel is adjusted to the required composition and temperature.
［溶製時の溶鋼成分測定方法］
溶鋼中のＡｌ濃度は、取鍋内の溶鋼から採取したサンプルを分析することで測定できる。また、溶鋼中の全Ｏ濃度（Ｔ．Ｏ濃度）は、特許文献４に記載の方法に基づいて迅速に分析できる。また、酸素濃淡電池を原理とする酸素濃度プローブで溶鋼の溶存酸素濃度を直接測定することができる。
[Method for measuring molten steel composition during smelting]
Al concentration in molten steel can be measured by analyzing a sample taken from molten steel in a ladle. Further, the total O concentration (TO concentration) in molten steel can be rapidly analyzed based on the method described in Patent Document 4. In addition, it is possible to directly measure the concentration of dissolved oxygen in molten steel with an oxygen concentration probe based on the principle of an oxygen concentration cell.
［効果の確認方法］
アルミナクラスタが低減されたか否かを確認する方法は、鋳片から検鏡用のミクロサンプルを切り出して樹脂埋め後に鏡面研磨し、その後、光学顕微鏡もしくはＥＤＳ付きの電子顕微鏡でミクロサンプル研磨面上の酸化物および硫化物の数、大きさおよび成分等を調査する。この調査において、視野面積１６０～２００ｍｍ2に存在する粒径１μｍ以上の酸化物（アルミナ）を調査し、酸化物中心間距離が５μｍ以下であるアルミナは同一のアルミナクラスタと評価し、同一のアルミナクラスタの最大粒径が２５μｍ以上になるアルミナクラスタを計数する。この時、鋳片でのアルミナクラスタの個数密度が０．３０個／ｍｍ2以下であった場合、アルミナクラスタ低減効果があったと判断できる。また、それぞれの試験にて鋳造性を調査し、アルミナクラスタ低減効果があり、かつ、ノズル閉塞傾向が見られなかった場合を、発明の効果が認められたと判断する。
[Method for confirming effect]
A method for confirming whether or not alumina clusters have been reduced is to cut out a micro sample for inspection from a cast piece, embed it in resin, and then mirror-polish it. Investigate the number, size and composition of oxides and sulfides. In this investigation, oxides (alumina) with a grain size of 1 μm or more existing in a visual field area of 160 to 200 mm 2 were investigated, and alumina with an oxide center-to-center distance of 5 μm or less was evaluated as the same alumina cluster, and the same alumina cluster was evaluated. Alumina clusters with a maximum grain size of 25 μm or more are counted. At this time, when the number density of alumina clusters in the slab was 0.30/mm 2 or less, it can be judged that there was an effect of reducing alumina clusters. In addition, the castability was investigated in each test, and if there was an effect of reducing alumina clusters and no nozzle clogging tendency was observed, it was judged that the effect of the invention was recognized.
次に、本発明の実施例について説明するが、実施例での条件は、本発明の実施可能性及び効果を確認するために採用した一条件例であり、本発明は、この一条件例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限りにおいて、種々の条件を採用し得るものである。 Next, examples of the present invention will be described. The conditions in the examples are one example of conditions adopted for confirming the feasibility and effect of the present invention, and the present invention is based on this one example of conditions. It is not limited. Various conditions can be adopted in the present invention as long as the objects of the present invention are achieved without departing from the gist of the present invention.
高炉から出銑された溶銑を、溶銑予備処理で脱硫処理し、転炉型精錬容器（ＣＶ、Ｃｏｎｖｅｒｔｅｒ）にて脱燐および脱炭処理した後、取鍋に溶鋼を出鋼した。出鋼の際、Ｓｉ、Ｍｎを含む合金元素を添加し、保温用のカバースラグを添加した。その後、取鍋に保持された溶鋼をＲＨ型真空脱ガス装置まで搬送し、浸漬管を溶鋼に浸漬させて真空槽内の圧力が１ｔｏｒｒ以下になるまで真空槽内を減圧した。そして、溶鋼中にＡｒガスからなる環流ガスを８．０ＮＬ／（ｍｉｎ・溶鋼ｔｏｎ）流し、溶鋼を環流させて脱炭処理を行った。溶鋼量は２５０ｔｏｎ規模であり、ＲＨ型真空脱ガス装置では、１５６０℃から１６１０℃の間で推移した。その結果、減圧処理（脱炭処理）後のｓｏｌ．Ａｌ濃度およびＴ．Ｏ濃度は、以下の表１に示す値であった。 Molten iron tapped from a blast furnace was desulfurized in hot metal pretreatment, dephosphorized and decarburized in a converter-type refining vessel (CV, Converter), and then tapped into a ladle. At the time of tapping, alloying elements including Si and Mn were added, and cover slag for heat retention was added. After that, the molten steel held in the ladle was conveyed to the RH type vacuum degassing device, the immersion tube was immersed in the molten steel, and the pressure in the vacuum chamber was reduced to 1 torr or less. Then, 8.0 NL/(min·ton of molten steel) of recirculating gas composed of Ar gas was flowed into the molten steel to circulate the molten steel for decarburization treatment. The amount of molten steel was on the scale of 250 tons, and in the RH type vacuum degassing device, it varied between 1560°C and 1610°C. As a result, the sol. Al concentration and T. The O concentration was the value shown in Table 1 below.
なお、表１のＮｏ．８のみ、ＲＨ型真空脱ガス装置で脱炭処理開始直後にＡｌを添加した。一方、表１のＮｏ．１からＮｏ．７、およびＮｏ．９からＮｏ．１５では、ＲＨ型真空脱ガス装置において、Ａｌを添加することなく１０～１５分の間、ＣとＯを反応させて脱炭処理を行った。なお、ｓｏｌ．Ａｌ濃度は、Ｎｏ．８を除いて脱炭処理前と同じ濃度であった。 In addition, No. in Table 1. No. 8, Al was added immediately after starting the decarburization treatment with the RH type vacuum degassing device. On the other hand, No. in Table 1. 1 to No. 7, and no. 9 to No. In 15, decarburization was performed by reacting C and O for 10 to 15 minutes without adding Al in an RH type vacuum degassing device. In addition, sol. The Al concentration is No. Except for 8, the concentrations were the same as before the decarburization treatment.
脱炭処理後、表１に示すそれぞれの溶鋼にミッシュメタルの状態でＲＥＭを添加し、その後、Ｎｏ．８を除いてＡｌを添加した。Ａｌを添加した後は、連続鋳造機にてスラブあるいはブルームといった半製品を製造した。そして、前述した手順で鋳片からは検鏡用のミクロサンプルを採取し、検鏡法により、鏡面研磨したサンプル研磨面上の粒径１μｍ以上の酸化物を調査した。その結果を表１に示す。鋳片でのアルミナクラスタの個数密度が０．３０個／ｍｍ2以下であった場合、アルミナクラスタ低減効果があったと判断した。 After the decarburization treatment, REM was added in the state of misch metal to each of the molten steels shown in Table 1. Al was added except for 8. After adding Al, semi-finished products such as slabs or blooms were produced using a continuous casting machine. Then, a micro sample for microscopy was taken from the slab by the procedure described above, and oxides having a grain size of 1 μm or more on the polished surface of the mirror-polished sample were examined by the microscopy method. Table 1 shows the results. When the number density of alumina clusters in the slab was 0.30/mm 2 or less, it was determined that there was an effect of reducing alumina clusters.
Ｎｏ．１からＮｏ．７は本発明例であり、いずれも質量％で脱炭処理前のｓｏｌ．Ａｌ濃度が０．００５０％以下、脱炭処理後のＴ．Ｏ濃度が０．００３０％以下であり、ＲＥＭ添加量が（１）式の範囲内で、且つＡｌを添加したタイミングがＲＥＭ添加完了してから１．５～３分後であった。その結果、全ての条件で鋳片でのアルミナクラスタの個数密度が０．３０個／ｍｍ2以下にできたことに加え、ノズル閉塞といった鋳造トラブルも無く溶製できた。 No. 1 to No. 7 is an example of the present invention. The Al concentration is 0.0050% or less, and the T.V. The O concentration was 0.0030% or less, the amount of REM added was within the range of formula (1), and the timing of Al addition was 1.5 to 3 minutes after the completion of REM addition. As a result, under all the conditions, the number density of alumina clusters in the cast slab was 0.30/mm 2 or less, and in addition, the smelting was completed without casting troubles such as clogging of nozzles.
Ｎｏ．８は、ＲＨ型真空脱ガス装置で脱炭処理開始直後にＡｌ添加した従来例である。溶鋼中のＯ濃度が高い段階からＡｌが添加されたため、アルミナクラスタの個数密度は高かった。また、Ｎｏ．９は、ｓｏｌ．ＲＨ型真空脱ガス装置での脱炭処理前後でｓｏｌ．Ａｌ濃度が質量％で０．００５０％よりも高い状態であったため、ＲＥＭ添加前の段階でアルミナクラスタが多く生成され、ＲＥＭを添加してもアルミナクラスタ低減効果が十分得られなかった。 No. No. 8 is a conventional example in which Al is added immediately after the start of decarburization treatment in the RH type vacuum degassing apparatus. Since Al was added from the stage when the O concentration in the molten steel was high, the number density of alumina clusters was high. Also, No. 9 is sol. The sol. Since the Al concentration was higher than 0.0050% by mass, a large amount of alumina clusters were formed before the addition of REM, and even with the addition of REM, the effect of reducing alumina clusters was not sufficiently obtained.
Ｎｏ．１０およびＮｏ．１１は、脱炭処理後のＲＥＭ添加前のＴ．Ｏ濃度が質量％で０．００３０％よりも高かったため、ＲＥＭ添加量が（１）式の範囲であったものの、ＲＥＭ酸化物が過剰に生成されたことによって、鋳造時にノズル閉塞傾向が確認された。 No. 10 and no. 11 is the T.V. before REM addition after decarburization. Since the O concentration was higher than 0.0030% by mass, the REM addition amount was within the range of formula (1), but due to the excessive generation of REM oxide, it was confirmed that the nozzle clogged during casting. rice field.
Ｎｏ．１２およびＮｏ．１３は、ＲＥＭ添加量が（１）式の下限よりも少なかった。このため、ＲＥＭ酸化物が不足して液体酸化鉄が生成してしまったため、アルミナクラスタの形成を低減できなかった。 No. 12 and no. In No. 13, the amount of REM added was less than the lower limit of formula (1). For this reason, since REM oxide was insufficient and liquid iron oxide was generated, the formation of alumina clusters could not be reduced.
Ｎｏ．１４は、ＲＥＭ添加完了からＡｌ添加までの時間が１．５分よりも短かった。このため、Ａｌ添加のタイミングではまだ溶鋼内でＲＥＭが均一に拡散されておらず、ＲＥＭが十分に拡散されていないところではＡｌを展開したことによってアルミナクラスタが形成されやすく、アルミナクラスタを低減できなかった。一方でＮｏ．１５は、ＲＥＭ添加完了からＡｌ添加までの時間が３．０分よりも長かった。このため、ＲＥＭによる脱酸効果が低下した状態、つまり液体酸化鉄の生成を抑制できない状態でＡｌを添加したため、アルミナクラスタの形成を低減できなかった。 No. In No. 14, the time from the completion of REM addition to the addition of Al was shorter than 1.5 minutes. Therefore, at the timing of Al addition, REM has not yet diffused uniformly in the molten steel, and in places where REM has not sufficiently diffused, alumina clusters are likely to be formed due to the expansion of Al, and alumina clusters can be reduced. I didn't. On the other hand, No. In No. 15, the time from the completion of REM addition to the addition of Al was longer than 3.0 minutes. Therefore, since Al was added in a state in which the deoxidizing effect of REM was lowered, that is, in a state in which the formation of liquid iron oxide could not be suppressed, the formation of alumina clusters could not be reduced.
Claims (1)
６１．２×％Ｔ．Ｏ≦Ｗ＿ＲＥＭ ・・・（１）
ここで、Ｗ＿ＲＥＭはＲＥＭ添加量（ｋｇ／ｔｏｎ）を表し、％Ｔ．Ｏは、ＲＥＭを添加する前の溶鋼中の全Ｏ濃度（質量％）を表す。 Using a vacuum degasser, sol. Molten steel having an Al concentration of 0.0050% by mass or less is circulated for decarburization, and the T.E. Reduce the O concentration to 0.0030% by mass or less, then add REM to the molten steel within the range of the following formula (1), and add Al within 1.5 to 3 minutes after the completion of REM addition. A melting method for Al-deoxidized steel, characterized by:
61.2 x %T. O≦W_REM (1)
Here, W_REM represents the amount of REM added (kg/ton), %T. O represents the total O concentration (mass%) in the molten steel before adding REM.
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| JP2002327239A (en) | 2001-05-07 | 2002-11-15 | Nippon Steel Corp | Slab for thin steel sheet with few defect caused by inclusion, and manufacturing method therefor |
| JP2004143510A (en) | 2002-10-23 | 2004-05-20 | Nippon Steel Corp | Method for melting steel sheet for extra low carbon or low carbon thin sheet having excellent surface quality, and continuously cast slab |
| JP2005002421A (en) | 2003-06-12 | 2005-01-06 | Nippon Steel Corp | Method for producing steel material with little alumina cluster |
| JP2012158789A (en) | 2011-01-31 | 2012-08-23 | Sumitomo Metal Ind Ltd | Method for desulfurizing molten metal using vacuum degassing apparatus |
| WO2013058131A1 (en) | 2011-10-20 | 2013-04-25 | 新日鐵住金株式会社 | Bearing steel and method for producing same |
| JP2013216927A (en) | 2012-04-05 | 2013-10-24 | Nippon Steel & Sumitomo Metal Corp | Method for producing high purity steel material |
| WO2013161794A1 (en) | 2012-04-23 | 2013-10-31 | 新日鐵住金株式会社 | Rail |
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