JP2018127680A - Method for smelting clean steel - Google Patents
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本発明は、製品特性を大きく悪化させ得る粗大な介在物、特に酸化物系介在物の生成を抑制することができる清浄鋼の溶製方法に関する。 The present invention relates to a method for producing clean steel capable of suppressing the formation of coarse inclusions, particularly oxide inclusions, which can greatly deteriorate product characteristics.
従来、転炉出鋼後の溶鋼中の過剰な酸素を除去する手法として、溶鋼にＡｌを添加して酸素をＡｌ2Ｏ3として除去するＡｌ脱酸という手法が一般的に採用されている。しかしながら、Ａｌ脱酸過程で生成されるＡｌ2Ｏ3系非金属介在物は非常に硬質であり、かつクラスターを形成して粗大化するため、鋼の製品特性を著しく低下させる。例えば、軸受鋼に代表される高清浄鋼では、Ａｌ2Ｏ3が破壊の起点となり、転動疲労寿命が大きく低下することが知られている。また、タイヤコード等に用いられている高炭素鋼線材は、熱間圧延で線材にした後、冷間引抜き（伸線加工）を行うことで製造されるが、鋼中に高硬度のＡｌ2Ｏ3が混入していると、加工途中での断線の原因となる。したがって、粗大なＡｌ2Ｏ3の生成を抑制することは極めて重要である。 Conventionally, as a technique for removing excess oxygen in molten steel after the converter steel, an Al deoxidation technique in which Al is added to the molten steel to remove oxygen as Al 2 O 3 has been generally employed. However, Al 2 O 3 -based non-metallic inclusions produced in the Al deoxidation process are very hard and coarsen by forming clusters, so that the product properties of the steel are significantly reduced. For example, in high clean steel represented by bearing steel, it is known that Al 2 O 3 serves as a starting point of fracture and the rolling fatigue life is greatly reduced. Moreover, high carbon steel wire material used in tire cords, etc., after the wire in the hot rolling, it is produced by performing a cold drawing (drawing) of high hardness in the steel Al 2 If O 3 is mixed, it may cause disconnection during processing. Therefore, it is extremely important to suppress the formation of coarse Al 2 O 3 .
そこで、このような介在物の生成抑制方法として、例えば特許文献１には、転炉から溶鋼を未脱酸出鋼し、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、結果として溶鋼中酸素濃度を１００ｐｐｍ以下とした後にＡｌを添加する方法が開示されている。この方法は、鋼中酸素をＣＯガスとして排出する減圧Ｃ脱酸反応を活用することで、介在物の生成自体を抑制する技術である。
しかしながら、この方法にはＣ脱酸を生じさせるための溶鋼中ＣおよびＡｌ濃度、さらには雰囲気圧力の条件について明示されておらず、条件によってはＣ脱酸反応が効率的に生じない可能性がある。
Therefore, as a method for suppressing the formation of such inclusions, for example, in Patent Document 1, the molten steel is undeoxidized from the converter, and the carbon-containing material is added to the molten steel until the oxygen concentration in the molten steel becomes 100 ppm or less. As a result, a method is disclosed in which Al is added after the oxygen concentration in molten steel is 100 ppm or less. This method is a technique for suppressing the formation of inclusions by utilizing a reduced pressure C deoxidation reaction in which oxygen in steel is discharged as CO gas.
However, this method does not clearly indicate the conditions of the C and Al concentrations in the molten steel for causing C deoxidation and the atmospheric pressure, and depending on the conditions, there is a possibility that the C deoxidation reaction may not occur efficiently. is there.
また、特許文献２には、以下の（４）式のＣ脱酸反応で決まる平衡酸素濃度が、以下の（５）式のＡｌ脱酸で決まる平衡酸素濃度を下回るＡｌ濃度範囲を明確化し、溶鋼のＡｌ濃度をこの範囲に制御した上で環流型脱ガス装置において環流処理を実施することを特徴とする、高清浄鋼の溶製方法が開示されている。
Ｃ＋Ｏ＝ＣＯ（ｇ） ・・・（４）
Ａｌ2Ｏ3（ｓ）＝２Ａｌ＋３Ｏ ・・・（５）
Patent Document 2 clarifies the Al concentration range in which the equilibrium oxygen concentration determined by the C deoxidation reaction of the following formula (4) is lower than the equilibrium oxygen concentration determined by the Al deoxidation of the following formula (5), There has been disclosed a method for melting highly clean steel, characterized in that the Al concentration of the molten steel is controlled within this range, and then the recirculation treatment is performed in the recirculation type degassing apparatus.
C + O = CO (g) (4)
Al 2 O 3 (s) = 2Al + 3O (5)
この方法では、Ｃ脱酸による介在物抑制効果を安定して活用することができる。しかしながら、環流型脱ガス装置でのＣ脱酸反応は、取鍋上面のスラグからの再酸化の影響を強く受ける。スラグからの再酸化が起こると、Ａｌ2Ｏ3以外にもＳｉＯ2やＭｎＯなどの介在物が溶鋼中に生成される可能性があり、これらの介在物も鋼の製品特性を著しく低下させる場合がある。したがって、Ｃ脱酸による介在物抑制効果を更に安定して活用するためには、再酸化の要因となるスラグ中のＦｅＯ，ＭｎＯといった低級酸化物を脱ガス処理前の段階で十分に低減させる必要がある。 In this method, the inclusion suppression effect by C deoxidation can be stably utilized. However, the C deoxidation reaction in the reflux degassing apparatus is strongly influenced by reoxidation from the slag on the upper surface of the ladle. When reoxidation from slag occurs, inclusions such as SiO 2 and MnO may be generated in the molten steel in addition to Al 2 O 3 , and these inclusions also significantly reduce the product properties of the steel There is. Therefore, in order to utilize the inclusion suppression effect by C deoxidation more stably, it is necessary to sufficiently reduce lower oxides such as FeO and MnO in the slag, which cause reoxidation, at the stage before degassing treatment. There is.
スラグ中の低級酸化物を還元する技術としては、特許文献３には、真空脱ガス装置においてＣとＯを減圧下で反応させる前段階として、取鍋スラグに金属ＡｌまたはＡｌドロスを添加してスラグ中の低級酸化物であるＦｅＯとＭｎＯを還元した後、ＭｇＯを添加してスラグを固化させることを特徴とする、高清浄度鋼の製造方法が開示されている。この方法は、Ａｌを溶鋼ではなくスラグ上面のみに散布し、溶鋼中Ａｌ濃度を増加させることなくＦｅＯ，ＭｎＯを還元させるとともに、ＭｇＯによりスラグを固化させ、スラグからの再酸化を抑制する技術である。
しかしながら、スラグ上面にＡｌおよびＭｇＯを散布させただけでは低級酸化物の還元反応が効率的に進行せず、かつ還元反応に寄与しなかったＡｌが溶鋼に溶解する可能性がある。したがって、脱ガス処理によってＡｌ2Ｏ3低減効果が得られない可能性がある。
As a technique for reducing lower oxides in slag, Patent Document 3 discloses that metal Al or Al dross is added to ladle slag as a pre-stage for reacting C and O under reduced pressure in a vacuum degassing apparatus. A method for producing a high cleanliness steel is disclosed, in which FeO and MnO, which are lower oxides in slag, are reduced and then MgO is added to solidify the slag. In this method, Al is sprayed only on the top surface of the slag, not the molten steel, and FeO and MnO are reduced without increasing the Al concentration in the molten steel, and the slag is solidified with MgO to suppress reoxidation from the slag. is there.
However, if Al and MgO are only sprayed on the upper surface of the slag, the reduction reaction of the lower oxide does not proceed efficiently, and Al that has not contributed to the reduction reaction may be dissolved in the molten steel. Therefore, the Al 2 O 3 reduction effect may not be obtained by the degassing process.
また、特許文献４には、取鍋内のスラグ表面にガスを吹き付けてスラグを冷却し、スラグ表面温度を溶鋼温度よりも１５０℃以上低下させることを特徴とする清浄鋼の溶製方法が開示されている。これは、ガス上吹きにてスラグを固めて、スラグからの再酸化反応そのものを抑制する技術である。
しかしながら、溶鋼と接触しているスラグ下部まで安定的に固化させることは難しく、かつ溶鋼温度の低下を招くという課題がある。
Patent Document 4 discloses a method for producing clean steel, characterized in that gas is blown onto the slag surface in the ladle to cool the slag and the slag surface temperature is lowered by 150 ° C. or more from the molten steel temperature. Has been. This is a technique for suppressing the reoxidation reaction itself from the slag by hardening the slag by blowing the gas.
However, there is a problem that it is difficult to stably solidify the lower part of the slag in contact with the molten steel, and the molten steel temperature is lowered.
上記したような従来の手法では、Ａｌを溶鋼中に溶解させずに、スラグ中ＦｅＯ，ＭｎＯの還元を効率よく実施することは困難である。すなわち、従来の手法では、溶鋼中での介在物の生成を安定的に抑制することは困難である。
そこで本発明は、溶鋼中の酸素を除去する方法として、Ａｌ等の還元剤を使用することなく、かつスラグを固化させることなくスラグ中のＦｅＯ及びＭｎＯ濃度を低減して溶鋼中の介在物を低減できる清浄鋼の溶製方法を提供することを目的とする。
In the conventional methods as described above, it is difficult to efficiently reduce FeO and MnO in slag without dissolving Al in molten steel. That is, with the conventional technique, it is difficult to stably suppress the formation of inclusions in the molten steel.
Therefore, the present invention provides a method for removing oxygen in molten steel by reducing the FeO and MnO concentrations in the slag without using a reducing agent such as Al, and without solidifying the slag, thereby removing inclusions in the molten steel. An object of the present invention is to provide a method for melting clean steel that can be reduced.
上述した課題を解決するためには、本発明者らは、真空脱ガス処理を実施する前段階の取鍋精錬において、Ｃによりスラグ中ＦｅＯおよびＭｎＯの還元を促進させることが有効と考えた。
ここで、上述した（４）式及び（５）式で決定される平衡酸素濃度は、各反応における平衡関係式からそれぞれ下記（６）式及び（７）式で表される。したがって、Ａｌ脱酸が生じずＣ脱酸のみが生じる条件は以下の（８）式で表すことができ、（６）式〜（８）式を解くことで、Ｃ脱酸が活用できるＡｌ濃度範囲はＣ濃度の関数として以下の（９）式で表すことができる。
［％Ｏ］C＝Ｃ6（定数）×ＰCO／［％Ｃ］ ・・・（６）
［％Ｏ］Al＝（Ｃ7（定数）／［％Ａｌ］2）2/3 ・・・（７）
［％Ｏ］C＜［％Ｏ］＜［％Ｏ］Al ・・・（８）
［％Ａｌ］＜Ｃ9（定数）×［％Ｃ］1.5 ・・・（９）
ここで、［％Ｏ］Al：Ａｌの酸化反応から求まる溶鋼中Ｏ濃度（質量％）、［％Ｏ］C：Ｃの酸化反応から求まる溶鋼中Ｏ濃度（質量％）、［％Ａｌ］：ｓｏｌ．Ａｌ濃度（質量％）、ＰCO：ＣＯ分圧（Ｔｏｒｒ）、［％Ｃ］：Ｃ濃度（質量％）、［％Ｏ］：溶存酸素濃度（質量％）である。
In order to solve the above-described problems, the present inventors considered that it is effective to promote the reduction of FeO and MnO in slag by C in the ladle refining before the vacuum degassing treatment.
Here, the equilibrium oxygen concentration determined by the above-described equations (4) and (5) is expressed by the following equations (6) and (7) from the equilibrium relational equations in each reaction. Therefore, the conditions under which Al deoxidation does not occur and only C deoxidation occurs can be expressed by the following equation (8), and the Al concentration at which C deoxidation can be utilized by solving equations (6) to (8) The range can be expressed by the following equation (9) as a function of C concentration.
[% O] C = C 6 (constant) × P CO / [% C] (6)
[% O] Al = (C 7 (constant) / [% Al] 2 ) 2/3 (7)
[% O] C <[% O] <[% O] Al (8)
[% Al] <C 9 (constant) × [% C] 1.5 (9)
Here, [% O] Al : O concentration (mass%) in molten steel determined from oxidation reaction of Al, [% O] C : O concentration (mass%) in molten steel determined from oxidation reaction of C, [% Al]: sol. Al concentration (mass%), P CO : CO partial pressure (Torr), [% C]: C concentration (mass%), [% O]: dissolved oxygen concentration (mass%).
本発明者らは、真空脱ガス処理中だけでなく、取鍋精錬中においてもＡｌ濃度を（７）式の範囲に制御した上でＣＯ分圧を低位に制御することで、溶鋼中のＣによりスラグ中のＦｅＯおよびＭｎＯの還元が可能と考えた。また、本発明者らは、溶鋼中Ｃによるスラグ中のＦｅＯおよびＭｎＯの還元速度は、ＣＯ分圧、Ｃ濃度、溶鋼の攪拌動力密度およびスラグ原単位（溶鋼１ｔｏｎ当たりのスラグ質量）と相関があることを見出し、還元に必要な取鍋精錬時間はこれらの関数で表すことが可能と考えた。 The inventors of the present invention not only during the vacuum degassing treatment but also during ladle refining, controlling the Al concentration within the range of the formula (7) and controlling the CO partial pressure to a low level, thereby reducing the C in the molten steel. It was considered that FeO and MnO in the slag can be reduced. Further, the present inventors have found that the reduction rate of FeO and MnO in slag by C in molten steel correlates with CO partial pressure, C concentration, stirring power density of molten steel, and slag unit (slag mass per ton of molten steel). I found out that there was a ladle refining time required for the reduction, and I thought that it was possible to express it with these functions.
上記の考えを踏まえ、本発明は、スラグ中のＦｅＯおよびＭｎＯを、取鍋精錬下でのＣ脱酸により真空脱ガス処理中に再酸化が生じないレベルまでスラグ中のＦｅＯおよびＭｎＯを還元が可能となる操業条件範囲を明らかとすることでなされたものであり、以下に記載の通りである。
（１）Ｃ：０．２〜１．２質量％、Ｓｉ：０．０３〜０．３質量％、Ｍｎ：０．１〜１．５質量％、Ｔｉ：０．０３質量％以下を含有する溶鋼を、不活性ガスによる底吹き攪拌下で取鍋精錬を実施した後、環流型脱ガス装置にて脱ガス処理を実施する清浄鋼の溶製方法であって、
出鋼後の溶鋼中のＡｌ濃度を（１）式の範囲に調整し、かつスラグ組成をＣａＯ／Ａｌ2Ｏ3：１．４〜２．０、ＣａＯ／ＳｉＯ2：２．５〜４．０、ＦｅＯ＋ＭｎＯ：５〜１５質量％に調整した後、前記取鍋精錬において、雰囲気ＣＯ分圧を８０Ｔｏｒｒ未満、溶鋼の攪拌動力密度を３０〜８０Ｗ／ｔｏｎに調整し、（２）式及び（３）式に示す条件で取鍋精錬処理を実施し、その後、Ａｌ及び強脱酸元素のいずれも新たに添加せずに、環流型脱ガス装置にて脱ガス処理を実施することを特徴とする清浄鋼の溶製方法。
［％Ａｌ］＜０．０３５×［％Ｃ］1.5 ・・・（１）
ｔLadle＞５５×（ＰCO／［％Ｃ］）0.28×ε-1.69×（ＷSlag／ＷSteel）1.29
・・・（２）
ε＝３７１ＧＴ／ＷSteel×｛ｌｎ（１＋７５ρSteelＨ／ＰLadle）＋０．０６（１−３００／Ｔ）｝ ・・・（３）
ここで、［％Ａｌ］：溶鋼中Ｓｏｌ．Ａｌ濃度（質量％）、［％Ｃ］：溶鋼中Ｃ濃度（質量％）、ｔLadle：取鍋精錬処理時間（ｍｉｎ）、ＰCO：取鍋内ＣＯ分圧（Ｔｏｒｒ）、ε：攪拌動力密度（Ｗ／ｔｏｎ）、ＷSlag：スラグ質量（ｋｇ）、ＷSteel：溶鋼質量（ｔｏｎ）、Ｇ：底吹き不活性ガス流量（Ｎｍ3／ｓ）、Ｔ：溶鋼温度（Ｋ）、ρSteel：溶鋼密度（ｔｏｎ／ｍ3）、Ｈ：取鍋内溶鋼の浴深（ｍ）、ＰLadle：取鍋内全圧（Ｔｏｒｒ）である。
ここで、攪拌動力密度εを定義する（３）式は非特許文献１に記載されており、本発明では、この関係式を用いた。
Based on the above idea, the present invention reduces FeO and MnO in slag to a level where reoxidation does not occur during vacuum degassing by C deoxidation under ladle refining. It was made by clarifying the range of operating conditions that can be achieved, and is as described below.
(1) C: 0.2 to 1.2% by mass, Si: 0.03 to 0.3% by mass, Mn: 0.1 to 1.5% by mass, Ti: 0.03% by mass or less A method for producing clean steel in which molten steel is subjected to ladle refining under bottom blowing stirring with an inert gas, and then degassed with a reflux degasser,
The Al concentration in the molten steel after steel is adjusted to the range of the formula (1), and the slag composition is CaO / Al 2 O 3 : 1.4 to 2.0, CaO / SiO 2 : 2.5 to 4 . After adjusting to 0, FeO + MnO: 5 to 15% by mass, in the ladle refining, the atmospheric CO partial pressure is adjusted to less than 80 Torr, and the stirring power density of the molten steel is adjusted to 30 to 80 W / ton. ) The ladle refining process is carried out under the conditions shown in the formula, and then the degassing process is carried out with a recirculation type degassing apparatus without newly adding any of Al and strong deoxidizing elements. A method for melting clean steel.
[% Al] <0.035 × [% C] 1.5 (1)
t Ladle > 55 × (P CO / [% C]) 0.28 × ε- 1.69 × (W Slag / W Steel ) 1.29
... (2)
ε = 371 GT / W Steel × {ln (1 + 75ρ Steel H / P Ladle ) +0.06 (1-300 / T)} (3)
Here, [% Al]: Sol. Al concentration (% by mass), [% C]: C concentration in molten steel (% by mass), t Ladle : Ladle refining treatment time (min), P CO : CO partial pressure in the ladle (Torr), ε: Stirring power Density (W / ton), W Slag : Slag mass (kg), W Steel : Molten steel mass (ton), G: Bottom blowing inert gas flow rate (Nm 3 / s), T: Molten steel temperature (K), ρ Steel : Molten steel density (ton / m 3 ), H: Bath depth (m) of molten steel in the ladle, P Ladle : Total pressure in the ladle (Torr).
Here, the expression (3) defining the stirring power density ε is described in Non-Patent Document 1, and this relational expression is used in the present invention.
本発明によれば、Alを使用することなく、かつ処理負荷を増加させることなくスラグ中のＦｅＯおよびＭｎＯを還元して脱ガス処理中の再酸化を抑制することが可能となり、Ｃ脱酸による介在物低減効果を安定して得ることができる。 According to the present invention, FeO and MnO in slag can be reduced without using Al and without increasing the processing load, and reoxidation during degassing can be suppressed. The inclusion reduction effect can be obtained stably.
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.
１．本発明における用語の定義
「取鍋精錬」とは、ＬＦやＶＡＤに代表される取鍋精錬処理中の雰囲気ＣＯ分圧を低下させた上で、取鍋内溶鋼およびスラグを不活性ガスにより底吹きにて攪拌させる処理を指す。「環流型脱ガス装置」とは、一般的にＲＨと呼称される真空槽を要する溶鋼処理装置である。「脱ガス処理」とは、溶鋼成分とスラグ成分とを所定の範囲に調整した後、環流型脱ガス装置の真空槽内にて（４）式のＣ脱酸反応を生じさせ、Ｃによる脱酸を行う処理のことを指す。また、「強脱酸元素」とは、酸素との親和力がＡｌと同等もしくはそれ以上に高い元素を指し、Ｔｉ、Ｚｒ、Ｃａ、Ｍｇおよび希土類元素（ＲＥＭ）がこれに該当する。
1. Definition of terms in the present invention “Ladle refining” means that the atmospheric CO partial pressure during ladle refining treatment represented by LF and VAD is reduced, and the molten steel and slag in the ladle are bottomed with an inert gas. Refers to the process of stirring by blowing. The “circulating degassing device” is a molten steel processing device that requires a vacuum chamber generally called RH. “Degassing treatment” means that after the molten steel component and the slag component are adjusted within a predetermined range, a C deoxidation reaction of the formula (4) is caused in a vacuum tank of a recirculation type degassing device, and degassing by C is performed. It refers to the treatment of acid. The “strong deoxidation element” refers to an element having an affinity for oxygen equal to or higher than that of Al, and corresponds to Ti, Zr, Ca, Mg, and rare earth elements (REM).
２．本発明に係る出鋼後の溶鋼組成（溶鋼全体に対する割合）
［Ｃ：０．２〜１．２質量％］
Ｃは、鋼の強度を決める重要元素である。本発明はＡｌキルド鋼のようなＡｌ濃度の高い鋼種への適用も想定しており、Ｃ濃度が低いと効率よくＣ脱酸を活用できない可能性があるため、Ｃ濃度の下限を０．２質量％とする。また、Ｃ濃度が高いほどＣ脱酸の効果は大きくなるが、Ｃ濃度が１．２質量％を超えると母材の硬度が大きくなり過ぎるため、加工性が著しく低下してしまう。また、Ｃが１．２質量％を超えると脱ガス処理後に脱炭処理を行う必要性が生じるため、本発明でのＣ濃度の上限は１．２質量％とする。
2. Molten steel composition after steelmaking according to the present invention (ratio to the entire molten steel)
[C: 0.2 to 1.2% by mass]
C is an important element that determines the strength of steel. The present invention also assumes application to steel types with a high Al concentration such as Al killed steel, and if the C concentration is low, there is a possibility that C deoxidation cannot be utilized efficiently. Mass%. Further, the higher the C concentration, the greater the effect of C deoxidation. However, if the C concentration exceeds 1.2% by mass, the hardness of the base material becomes too high, and the workability is significantly reduced. Moreover, since it will be necessary to perform a decarburization process after a degassing process when C exceeds 1.2 mass%, the upper limit of C density | concentration in this invention shall be 1.2 mass%.
［Ｓｉ：０．０３〜０．３０質量％］
Ｓｉは、鋼材の焼き入れ性および強度を高める重要な元素であり、かつ溶鋼の酸素濃度を低位に維持するために最低限必要であるため、転炉出鋼直後の時点で少なくとも０．０３質量％は含有させる必要がある。しかし、Ｓｉ濃度が０．３０質量％を上回るとＳｉ脱酸が顕著に生じ、ＳｉＯ2系酸化物が大量に生成して溶鋼の清浄度が悪化する可能性があるため、０．３０質量％を上限とする。
[Si: 0.03-0.30 mass%]
Si is an important element that enhances the hardenability and strength of the steel material, and is at least necessary to maintain the oxygen concentration of the molten steel at a low level. Therefore, at least 0.03 mass immediately after converter steel output. % Must be included. However, when the Si concentration exceeds 0.30% by mass, Si deoxidation occurs remarkably, and there is a possibility that a large amount of SiO 2 oxide is generated and the cleanliness of the molten steel is deteriorated. Is the upper limit.
［Ｍｎ：０．１〜１．５質量％］
ＭｎもＳｉと同様に、鋼材の強度を高める重要な元素であり、かつ溶鋼の酸素濃度を低位維持するために最低限必要であるため、転炉出鋼直後の時点で０．１質量％は含有させる必要がある。しかし、Ｍｎ濃度が高過ぎると、Ｓｉと同様にＭｎＯ系酸化物が大量に生成する可能性があるため、１．５質量％を上限とする。
[Mn: 0.1 to 1.5% by mass]
Similar to Si, Mn is an important element that increases the strength of the steel material, and is the minimum necessary to maintain the oxygen concentration of the molten steel at a low level. It is necessary to contain. However, if the Mn concentration is too high, a large amount of MnO-based oxides may be generated in the same manner as Si, so the upper limit is 1.5% by mass.
［（１）式条件：［％Ａｌ］＜０．０３５×［％Ｃ］1.5］
取鍋精錬でのＣによるＦｅＯおよびＭｎＯの還元、ならびに環流脱ガス装置での脱ガス処理を行うためには、Ｃ脱酸がＡｌ脱酸よりも優勢な条件に制御する必要がある。（１）式の条件は（６）式の形で記述でき、（６）式の右辺の係数（Ｃ6）を鋭意検討により求めることで（１）式の条件を得ることができた。したがって、出鋼後から取鍋精錬開始までの間に、Ａｌ濃度およびＣ濃度が（１）式の条件を満たすように制御する必要がある。なお、取鍋精錬の時点で（１）式の範囲に制御出来ていれば、脱ガス処理時もほぼこの範囲に制御可能となる。
[(1) Formula condition: [% Al] <0.035 × [% C] 1.5 ]
In order to perform reduction of FeO and MnO by C in ladle refining and degassing treatment in a reflux degassing apparatus, it is necessary to control C deoxidation to prevail conditions over Al deoxidation. The condition of the expression (1) can be described in the form of the expression ( 6 ), and the condition of the expression (1) can be obtained by earnestly examining the coefficient (C 6 ) on the right side of the expression (6). Therefore, it is necessary to control the Al concentration and the C concentration so as to satisfy the condition of the expression (1) between the time of steel output and the start of ladle refining. In addition, if it can control to the range of (1) Formula at the time of ladle refining, it will become controllable to this range also at the time of a degassing process.
３．鋼材の機械特性の観点から鋼中に含有することが許容される成分濃度範囲
本発明で溶製する清浄鋼には、対象となる溶鋼に製品に必要な機能を付加する目的で、合金元素を含有させることも原理的に許容される。具体的には、Ｆｅの一部に加えて、Ｃｒ：１．７質量％以下、Ｍｏ：１．０質量％以下、Ｖ：０．３質量％以下、Ｎｉ：２．０質量％以下を含有させてもよい。また、不可避的不純物としてＰ：０．０３質量％以下、Ｓ：０．０３質量％以下、Ｍｇ：０．００２質量％以下、Ｃａ：０．００２質量％以下、Ｎ：０．０２質量％以下を含有していてもよい。ただし、取鍋精錬処理後から環流型脱ガス装置にて脱ガス処理を実施するまでの間にＡｌあるいは強脱酸元素を添加してしまうと、脱ガス処理中にＣ脱酸が生じず溶鋼の清浄化がなされない懸念があるため、上述した時期にＡｌあるいは強脱酸元素を添加しないようにする。
3. Ingredient concentration range allowed to be contained in steel from the viewpoint of mechanical properties of steel material In the clean steel melted in the present invention, an alloy element is added for the purpose of adding a necessary function to the product to the target molten steel. Inclusion in principle is also permitted. Specifically, in addition to a part of Fe, Cr: 1.7% by mass or less, Mo: 1.0% by mass or less, V: 0.3% by mass or less, Ni: 2.0% by mass or less You may let them. Further, as inevitable impurities, P: 0.03% by mass or less, S: 0.03% by mass or less, Mg: 0.002% by mass or less, Ca: 0.002% by mass or less, N: 0.02% by mass or less May be contained. However, if Al or a strong deoxidizing element is added between the ladle refining process and the degassing process in the reflux degassing apparatus, C deoxidation does not occur during the degassing process. Therefore, Al or a strong deoxidizing element should not be added at the above-mentioned time.
４．本発明に係る出鋼後のスラグ組成
［ＣａＯ／Ａｌ2Ｏ3：１．４〜２．０］
取鍋精錬下における溶鋼−スラグ間反応を効率的に実施するためには、スラグの粘度を低下させるとともに、スラグ液相率を高位に維持することが重要となる。ＣａＯ／Ａｌ2Ｏ3が低すぎるとスラグ粘度が大きく増加してしまうため、１．４を下限とする。一方で、ＣａＯ／Ａｌ2Ｏ3が高すぎるとスラグの液相率が大きく低下してしまうため、２．０を上限とする。
4). Slag composition after steelmaking according to the present invention [CaO / Al 2 O 3 : 1.4 to 2.0]
In order to efficiently carry out the reaction between molten steel and slag under ladle refining, it is important to reduce the viscosity of the slag and maintain the slag liquid phase ratio at a high level. If CaO / Al 2 O 3 is too low, the slag viscosity will increase greatly, so 1.4 is the lower limit. On the other hand, if CaO / Al 2 O 3 is too high, the liquid phase ratio of the slag is greatly reduced, so 2.0 is the upper limit.
［ＣａＯ／ＳｉＯ2：２．５〜４．０］
スラグ中のＳｉＯ2はスラグの融点を低下させて液相率を増加させる効果があるため、スラグ中に最低限のＳｉＯ2が含有されている必要があり、ＣａＯ／ＳｉＯ2の上限を４．０とする。一方で、ＳｉＯ2はＣａＯやＡｌ2Ｏ3と比較すると酸素との親和性が弱く、スラグ中にＳｉＯ2が過剰に含有されるとＳｉＯ2がＳｉとＯとに分離して溶鋼中での再酸化の要因となるため、ＣａＯ／ＳｉＯ2の下限を２．５とする。
[CaO / SiO 2 : 2.5 to 4.0]
Since SiO 2 in the slag has the effect of lowering the melting point of the slag and increasing the liquid phase rate, the minimum amount of SiO 2 needs to be contained in the slag, and the upper limit of CaO / SiO 2 is 4. 0. On the other hand, SiO 2 is weak affinity for oxygen when compared to CaO and Al 2 O 3, the SiO 2 is excessively contained in the slag SiO 2 is in the molten steel is separated into Si and O Since it causes reoxidation, the lower limit of CaO / SiO 2 is set to 2.5.
［ＦｅＯ＋ＭｎＯ：５〜１５質量％（スラグ全体に対する割合）］
スラグ中のＦｅＯおよびＭｎＯは溶鋼での再酸化の要因となり、取鍋精錬前の段階で１５％を超えていると、取鍋精錬の現実的な処理時間内にこれらの低級酸化物を還元し切れない可能性があるため、スラグ全体に対して合計で１５質量％を上限とする。一方で、ＦｅＯおよびＭｎＯはスラグの融点を低下させる成分であり、出鋼直後に液相スラグを効率的に生成させる必要があるため、スラグ全体に対して合計で５質量％を下限とする。なお、本発明により、取鍋精錬後のスラグ中のＦｅＯ濃度およびＭｎＯ濃度の合計を１．０質量％未満にするものとするが、取鍋精錬前の段階で１．０質量％未満にすると、ＣａＯやＳｉＯ2などを大量に添加する必要があり操業上困難であることから、取鍋精錬前の段階では合計で５質量％を下限とする。
[FeO + MnO: 5 to 15% by mass (ratio to the whole slag)]
FeO and MnO in the slag cause reoxidation in the molten steel. If it exceeds 15% in the stage before ladle refining, these lower oxides are reduced within the practical processing time of ladle refining. Since it may not be cut, the upper limit is 15% by mass in total with respect to the entire slag. On the other hand, FeO and MnO are components that lower the melting point of slag, and it is necessary to efficiently generate liquid phase slag immediately after steeling out. Therefore, the lower limit is 5% by mass in total with respect to the entire slag. According to the present invention, the total FeO concentration and MnO concentration in the slag after ladle refining is set to less than 1.0% by mass. Since it is necessary to add a large amount of CaO, SiO 2 and the like and it is difficult to operate, a total of 5% by mass is made the lower limit before the ladle refining.
本発明で使用するスラグには、上記以外に、スラグに必要な機能を付加する目的で、ＭｇＯ：５．０質量％以下、Ｆ：１０質量％以下、Ｔｉ2Ｏ3：５．０質量％以下を含有させてもよい。また、不可避的不純物としてＰ2Ｏ5：１．０質量％以下、Ｓ：５．０質量％以下程度が許容される。 In addition to the above, the slag used in the present invention includes MgO: 5.0% by mass or less, F: 10% by mass or less, Ti 2 O 3 : 5.0% by mass for the purpose of adding functions necessary for the slag. The following may be included. Further, P 2 O 5 : 1.0 mass% or less and S: 5.0 mass% or less are allowed as inevitable impurities.
５．本発明に係る取鍋精錬処理条件
［雰囲気ＣＯ分圧：８０Ｔｏｒｒ未満］
（２）式からもわかるように、Ｃ脱酸反応は雰囲気ＣＯ分圧が低位であるほど顕著に生じるため、取鍋精錬中の雰囲気ＣＯ分圧は８０Ｔｏｒｒ未満とする。
5). Ladle refining treatment conditions according to the present invention [atmosphere CO partial pressure: less than 80 Torr]
As can be seen from the equation (2), the C deoxidation reaction is more prominent as the atmospheric CO partial pressure is lower, so the atmospheric CO partial pressure during ladle refining is less than 80 Torr.
［攪拌動力密度ε：３０〜８０Ｗ／ｔｏｎ］
一般的に溶鋼−スラグ間反応は溶鋼の攪拌動力密度が高いほど顕著に生じることが知られており、スラグ中のＦｅＯおよびＭｎＯを効率的に還元させるためには少なくとも３０Ｗ／ｔｏｎは確保する必要がある。一方で、攪拌動力密度を過度に増加させると取鍋固体酸化物の著しい損耗が生じ、この損耗に伴って溶鋼再酸化が顕著となり溶鋼清浄度の悪化を招く懸念があるため、８０Ｗ／ｔｏｎを上限とする。前述したように、攪拌動力密度の計算式は非特許文献１に記載された（３）式を用いる。
[Stirring power density ε: 30 to 80 W / ton]
Generally, it is known that the reaction between molten steel and slag is more noticeable as the stirring power density of the molten steel is higher. In order to reduce FeO and MnO in the slag efficiently, it is necessary to ensure at least 30 W / ton. There is. On the other hand, if the stirring power density is excessively increased, significant ladle solid oxide wear occurs, and there is a concern that reoxidation of the molten steel becomes noticeable with this wear, leading to deterioration of the cleanliness of the molten steel. The upper limit. As described above, the formula (3) described in Non-Patent Document 1 is used as the calculation formula for the stirring power density.
［（２）式条件：ｔLadle＞５５×（ＰCO／［％Ｃ］）0.28×ε-1.69×（ＷSlag／ＷSteel）1.29］
スラグ中のＦｅＯおよびＭｎＯをＣにより還元させるためには一定以上の時間を要し、還元に必要な時間を決定する因子として、ＣＯ分圧、Ｃ濃度、攪拌動力密度およびスラグと溶鋼との質量比が挙げられる。本発明者らは、後述する効果の確認方法に則り、（１）式の条件を満たした上で、発明の効果を得るために必要な取鍋精錬処理時間と上記の因子との関係を鋭意検討し、（２）式の条件を得た。図１に、（１）式の条件を満たした上での（２）式で計算された右辺の値と、取鍋精錬処理時間ｔLadleの実績とを比較した結果を示すが、本発明の効果が得られたものは全て（２）式の条件を満たしていることがわかる。したがって、本発明の効果を得るためには、取鍋精錬処理時間ｔLadleを（２）式の条件を満たすように設定する必要がある。
[(2) Formula Condition: t Ladle > 55 × (P CO / [% C]) 0.28 × ε -1.69 × (W Slag / W Steel ) 1.29 ]
It takes a certain amount of time to reduce FeO and MnO in the slag with C, and factors that determine the time required for the reduction include CO partial pressure, C concentration, stirring power density, and mass of the slag and molten steel. Ratio. In accordance with a method for confirming the effect described later, the present inventors have earnestly established the relationship between the ladle refining treatment time necessary for obtaining the effect of the invention and the above factors after satisfying the condition of the expression (1). The conditions of the formula (2) were obtained. FIG. 1 shows the result of comparing the value of the right side calculated by the formula (2) after satisfying the condition of the formula (1) with the actual result of the ladle refining treatment time t Ladle . It can be seen that all the obtained effects satisfy the condition of the expression (2). Therefore, in order to obtain the effect of the present invention, it is necessary to set the ladle refining treatment time t Ladle so as to satisfy the condition of the expression (2).
６．処理条件
本発明において、転炉から出鋼された溶鋼は、まず取鍋精錬処理にてスラグ改質が実施された後、環流型脱ガス装置にて脱ガス処理される。転炉等の精錬容器から取鍋に出鋼され、取鍋精錬装置まで搬送されて処理を行う前に、上記の溶鋼成分範囲に調整する目的で、合金等の添加を行うことが望ましい。具体的には、取鍋精錬処理を開始する前に、溶鋼およびスラグ組成を所定の範囲に調整することである。成分調整後の溶鋼およびスラグからサンプルを採取し、迅速分析にて成分濃度を得るとともに、スラグの厚みを測定し、取鍋断面積およびスラグ密度からスラグ質量ＷSlagを算出する。
6). Treatment conditions In the present invention, the molten steel discharged from the converter is first subjected to slag reforming in a ladle refining treatment and then degassed in a circulating degassing apparatus. It is desirable to add an alloy or the like for the purpose of adjusting to the above-mentioned molten steel component range before being processed into a ladle from a refining vessel such as a converter and transported to a ladle refining device. Specifically, before starting the ladle refining process, the molten steel and the slag composition are adjusted to a predetermined range. Samples are taken from the molten steel and slag after component adjustment, the component concentration is obtained by rapid analysis, the thickness of the slag is measured, and the slag mass W Slag is calculated from the ladle cross-sectional area and slag density.
上記操作を終えた溶鋼およびスラグは取鍋精錬装置まで搬送され、取鍋底部の底吹き羽口から不活性ガスを導入して攪拌、かつ容器内の雰囲気ＣＯ分圧を８０Ｔｏｒｒ未満の水準まで低下させて取鍋精錬処理を開始する。ここで、雰囲気ＣＯ分圧を低下させる具体的な方法として容器内の不活性ガスによる置換、減圧が挙げられ、その手法としていずれの方法でも問題はないが、設備負荷の観点から不活性ガスによる容器内の置換が望ましく、さらには操業コストの観点から不活性ガスとして安価なＡｒを使用することが望ましい。さらに、取鍋精錬処理を開始する前に測定したＣ濃度、スラグ質量、底吹き不活性ガス流量から（３）式で算出される攪拌動力密度εを計算し、容器内雰囲気のガス分析で得られたＣＯ分圧から、（２）式を用いて取鍋精錬処理時間ｔLadleを決定する。 The molten steel and slag after the above operation are transported to the ladle refining equipment, and inert gas is introduced from the bottom blowing tuyeres at the bottom of the ladle and stirred, and the atmospheric CO partial pressure in the container is reduced to a level of less than 80 Torr. Let the ladle refining process start. Here, specific methods for lowering the atmospheric CO partial pressure include replacement with an inert gas in the container and pressure reduction, and there is no problem with any of the methods, but with an inert gas from the viewpoint of equipment load. It is desirable to replace the inside of the container, and it is desirable to use inexpensive Ar as an inert gas from the viewpoint of operation cost. Furthermore, the stirring power density ε calculated by the equation (3) is calculated from the C concentration, slag mass, and bottom blown inert gas flow rate measured before starting the ladle refining process, and obtained by gas analysis of the atmosphere in the container. From the obtained CO partial pressure, the ladle refining treatment time t Ladle is determined using equation (2).
取鍋精錬を終えた溶鋼は、Ａｌおよび強脱酸元素を新たに添加することなく、環流型真空脱ガス装置において脱ガス処理される。脱ガス処理は通常５０Ｔｏｒｒ未満の高真空下で処理されるため、Ａｌ濃度を（１）式の範囲に制御すればＣ脱酸が優先的に生じる条件となる。 The molten steel that has been subjected to ladle refining is degassed in a reflux-type vacuum degassing apparatus without newly adding Al and a strong deoxidizing element. Since the degassing process is usually performed under a high vacuum of less than 50 Torr, if the Al concentration is controlled within the range of the formula (1), the condition for preferentially generating C deoxidation is obtained.
７．効果の確認方法
本発明の効果は、取鍋精錬後のスラグ中のＦｅＯ濃度およびＭｎＯ濃度の合計、脱ガス処理後の酸化物系介在物の個数密度にて評価する。スラグ中のＦｅＯ濃度およびＭｎＯ濃度の合計は、取鍋精錬後の溶鋼上面のスラグからサンプルを採取し、化学分析に供することで得ることができる。酸化物系介在物の個数密度は、脱ガス処理後に採取した溶鋼のボンブサンプルを切断、樹脂埋め、研磨した後に切断面を光学顕微鏡で観察し、検鏡範囲内（＝２００ｍｍ2）に存在する５．０μｍ以上２０μｍ未満の介在物の個数を計測することで評価する。ただし、本発明ではＡｌを殆ど添加しないため、酸化物系介在物はＡｌ2Ｏ3以外にＳｉＯ2、ＭｎＯ、Ｔｉ2Ｏ3が主成分となる可能性があり、Ａｌ2Ｏ3系介在物のみ評価したのでは本発明による介在物低減効果を充分に確認できない。そこで、エネルギー分散型Ｘ線アナライザーを具備した走査電子顕微鏡で測定した際、Ａｌ、Ｓｉ、Ｍｎ、Ｔｉ、Ｃａ、ＭｇおよびＯの占める割合が９０ａｔｍ％以上であるものを介在物として計測する。本発明において、取鍋精錬後のスラグ中のＦｅＯ濃度およびＭｎＯ濃度の合計が１．０質量％未満、かつ５．０μｍ以上２０μｍ未満の酸化物系介在物の個数密度が１０個／ｍｍ2未満であったものを、発明の効果が得られたと判断することができる。
7). Method for confirming the effect The effect of the present invention is evaluated by the sum of the FeO concentration and the MnO concentration in the slag after ladle refining, and the number density of oxide inclusions after the degassing treatment. The total of the FeO concentration and the MnO concentration in the slag can be obtained by taking a sample from the slag on the upper surface of the molten steel after ladle refining and subjecting it to chemical analysis. The number density of oxide inclusions is within the microscopic range (= 200 mm 2 ) after observing the cut surface with an optical microscope after cutting, filling and polishing a bomb sample of molten steel collected after degassing treatment. Evaluation is made by measuring the number of inclusions of 5.0 μm or more and less than 20 μm. However, since the present invention without addition little Al, oxide-based inclusions may SiO 2, MnO, the Ti 2 O 3 as a main component other than Al 2 O 3, Al 2 O 3 inclusions However, the inclusion reduction effect according to the present invention cannot be sufficiently confirmed. Then, when it measures with the scanning electron microscope which equipped the energy dispersive X-ray analyzer, the thing for which the ratio for which Al, Si, Mn, Ti, Ca, Mg, and O account for 90 atm% or more is measured as an inclusion. In the present invention, the total density of FeO concentration and MnO concentration in the slag after ladle refining is less than 1.0 mass%, and the number density of oxide inclusions of 5.0 μm or more and less than 20 μm is less than 10 pieces / mm 2. It can be determined that the effect of the invention was obtained.
次に、本発明を実施例に基づいて更に説明するが、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, the present invention will be further described based on examples, but the conditions in the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention. It is not limited to the example conditions. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
転炉から出鋼直後の溶鋼およびスラグに対し成分調整を実施し、表１に示す組成の溶鋼およびスラグを得た。
次に、表１に示す組成の溶鋼とスラグを、取鍋とともに取鍋精錬装置であるＬＦまで搬送し、表２に示す条件にて取鍋精錬処理を行った。なお、発明例（実施例）、比較例とも全て、溶鋼量ＷSteelは８０ｔｏｎ、溶鋼温度Ｔは１８７３Ｋ、取鍋内溶鋼の浴深Ｈは２．６ｍ、取鍋内全圧ＰTotalは７６０Ｔｏｒｒであった。また、上記計算において、溶鋼の密度ρSteelは７ｔｏｎ／ｍ3とした。
Component adjustment was performed on the molten steel and slag immediately after the steel from the converter, and molten steel and slag having the compositions shown in Table 1 were obtained.
Next, the molten steel and slag having the composition shown in Table 1 were transported together with the ladle to LF, which is a ladle refining device, and ladle refining treatment was performed under the conditions shown in Table 2. In all of the inventive examples (examples) and comparative examples, the molten steel amount W Steel is 80 ton, the molten steel temperature T is 1873 K, the bath depth H of the molten steel in the ladle is 2.6 m, and the total pressure P Total in the ladle is 760 Torr. there were. In the above calculation, the density ρ Steel of the molten steel was 7 ton / m 3 .
取鍋精錬開始前には、溶鋼サンプルを採取してＣ濃度を測定し、スラグ厚みの測定によりスラグ質量ＷSlagを算出した。また、取鍋精錬中には容器内のガス分析を実施し、雰囲気ＣＯ分圧ＰCOを測定した。さらに取鍋精錬後のスラグを採取することで取鍋精錬後のＦｅＯ濃度およびＭｎＯ濃度を得た。 Prior to the start of ladle refining, a molten steel sample was collected, the C concentration was measured, and the slag mass W Slag was calculated by measuring the slag thickness. Further, during ladle refining, gas analysis in the container was performed, and the atmospheric CO partial pressure PCO was measured. Furthermore, by collecting slag after ladle refining, FeO concentration and MnO concentration after ladle refining were obtained.
また、取鍋精錬後にはＲＨ環流脱ガス装置にて脱ガス処理を実施した。そして、脱ガス処理直後に溶鋼サンプルを採取し、溶鋼サンプルから検鏡用のミクロサンプルを切り出した。前述した効果の確認方法に従って、ミクロサンプルから検鏡法にて介在物個数を計測した後、ＥＤＳ付属の走査型電子顕微鏡にて酸化物組成を測定した。ＲＨ真空脱ガス装置で処理した後は、連続鋳造法によってブルームあるいはビレットといった半製品を得た。
各試験における取鍋精錬処理後のスラグ中の（ＦｅＯ＋ＭｎＯ）濃度、および脱ガス処理後の最終的な溶鋼中介在物個数密度を表２に示す。
Moreover, after the ladle refining, the degassing process was implemented with the RH recirculation degassing apparatus. And the molten steel sample was extract | collected immediately after the degassing process, and the micro sample for speculum was cut out from the molten steel sample. According to the method for confirming the effect described above, the number of inclusions was measured from a micro sample by a spectroscopic method, and then the oxide composition was measured by a scanning electron microscope attached to EDS. After processing with the RH vacuum degassing apparatus, a semi-finished product such as bloom or billet was obtained by a continuous casting method.
Table 2 shows the (FeO + MnO) concentration in the slag after the ladle refining treatment and the final inclusion number density in the molten steel after the degassing treatment in each test.
表１及び表２に示すように、実施例であるＣｈ．Ｎｏ．１〜６は、本発明の条件を全て満たしていたため、取鍋精錬後のスラグ中のＦｅＯ濃度およびＭｎＯ濃度の合計が１質量％未満であり、かつ脱ガス処理後の介在物個数密度が１０個／ｍｍ2未満であったため、発明の効果が顕著に得られた。 As shown in Table 1 and Table 2, Ch. No. 1 to 6 satisfied all the conditions of the present invention, so the total of FeO concentration and MnO concentration in the slag after ladle refining was less than 1% by mass, and the inclusion number density after degassing treatment was 10 Since it was less than pieces / mm 2 , the effect of the invention was remarkably obtained.
また、以下の比較例の結果から、本発明により介在物の生成抑制効果を得るには、前述の条件を全て満たす必要があることが分かった。
表１及び表２のＣｈ．Ｎｏ．７〜２７は、本発明の条件を一部満たしていなかったため発明の効果が得られなかったものである。
In addition, from the results of the following comparative examples, it was found that all the above-described conditions must be satisfied in order to obtain the inclusion formation suppressing effect according to the present invention.
In Table 1 and Table 2, Ch. No. Nos. 7 to 27 did not satisfy the conditions of the present invention, and thus the effects of the invention could not be obtained.
Ｃｈ．Ｎｏ．７は溶鋼のＣ濃度が０．２質量％を下回っていたため、Ｃによりスラグ中のＦｅＯおよびＭｎＯを効率的に還元できなかった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。この結果から、出鋼直後の溶鋼中Ｃ濃度は０．２質量％以上である必要があることが確認できた。 Ch. No. In No. 7, since the C concentration of the molten steel was less than 0.2 mass%, FeO and MnO in the slag could not be efficiently reduced by C. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. From this result, it was confirmed that the C concentration in the molten steel immediately after the steel output needs to be 0.2% by mass or more.
Ｃｈ．Ｎｏ．８はＳｉ濃度が０．０３質量％を下回っていたため、溶鋼の脱酸不足で溶鋼中の酸素濃度が高くなりすぎ、スラグ中のＦｅＯおよびＭｎＯの還元不良が生じてしまった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。一方で、Ｃｈ．Ｎｏ．９はＳｉ濃度が０．３質量％を上回っていたため、スラグ中のＦｅＯおよびＭｎＯを効率的に還元することができたが、Ｓｉ脱酸が顕著に生じてＳｉＯ2系介在物が大量に生成してしまった。この結果から、出鋼後の溶鋼中Ｓｉ濃度は０．０３〜０．３質量％の範囲に制御する必要があることが確認できた。 Ch. No. In No. 8, since the Si concentration was less than 0.03% by mass, the oxygen concentration in the molten steel became too high due to insufficient deoxidation of the molten steel, resulting in poor reduction of FeO and MnO in the slag. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. On the other hand, Ch. No. 9 had a Si concentration higher than 0.3% by mass, so it was possible to efficiently reduce FeO and MnO in the slag, but Si deoxidation occurred significantly and a large amount of SiO 2 inclusions were produced. have done. From this result, it was confirmed that the Si concentration in the molten steel after the steel was required to be controlled in the range of 0.03 to 0.3% by mass.
Ｃｈ．Ｎｏ．１０は、Ｍｎ濃度が０．１質量％を下回っていたため、Ｓｉの場合と同様溶鋼の脱酸不足で酸素濃度が高くなりすぎ、スラグ中のＦｅＯおよびＭｎＯの還元不良が生じてしまった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。一方で、Ｃｈ．Ｎｏ．１１はＭｎ濃度が１．５質量％を上回っていたため、スラグ中のＦｅＯおよびＭｎＯを効率的に還元することができたが、Ｍｎ脱酸が顕著に生じてＭｎＯ系介在物が大量に生成してしまった。この結果から、出鋼後の溶鋼中Ｍｎ濃度は０．１〜１．５質量％の範囲に制御する必要がある。 Ch. No. In No. 10, since the Mn concentration was less than 0.1% by mass, the oxygen concentration became too high due to insufficient deoxidation of the molten steel as in the case of Si, resulting in poor reduction of FeO and MnO in the slag. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. On the other hand, Ch. No. 11 had a Mn concentration higher than 1.5% by mass, and thus was able to efficiently reduce FeO and MnO in the slag, but Mn deoxidation occurred significantly and a large amount of MnO-based inclusions were generated. I have. From this result, it is necessary to control the Mn concentration in the molten steel after steelmaking to a range of 0.1 to 1.5 mass%.
Ｃｈ．Ｎｏ．１２は、Ｔｉ濃度が０．０３質量％を上回っていたため、スラグ中のＦｅＯおよびＭｎＯを効率的に還元することができたが、Ｔｉ脱酸が顕著に生じてＴｉ2Ｏ3系介在物が大量に生成してしまった。この結果から、出鋼後の溶鋼中Ｔｉ濃度は０．０３質量％以下の範囲に制御する必要があることが確認できた。 Ch. No. No. 12, since the Ti concentration exceeded 0.03% by mass, FeO and MnO in the slag could be efficiently reduced. However, Ti deoxidation occurred remarkably, and Ti 2 O 3 inclusions were A large amount has been generated. From this result, it has been confirmed that the Ti concentration in the molten steel after steel is required to be controlled within a range of 0.03% by mass or less.
Ｃｈ．Ｎｏ．１３は、スラグ中のＣａＯ／Ａｌ2Ｏ3が１．４を下回っていたため、スラグ液相率は十分確保されていたもののスラグの粘度が増加して流動性が大きく悪化し、スラグ中のＦｅＯおよびＭｎＯの還元不良が生じてしまった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。一方で、Ｃｈ．Ｎｏ．１４はスラグ中のＣａＯ／Ａｌ2Ｏ3が２．０を上回っていたため、スラグ液相率が大きく低下したことによってスラグの流動性が低下し、スラグ中のＦｅＯおよびＭｎＯの還元不良が生じてしまった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。以上の結果から、出鋼後のスラグ中のＣａＯ／Ａｌ2Ｏ3は１．４〜２．０の範囲に制御する必要があることが確認できた。 Ch. No. In No. 13, since CaO / Al 2 O 3 in the slag was less than 1.4, the slag liquid phase ratio was sufficiently secured, but the viscosity of the slag increased and the fluidity was greatly deteriorated, and FeO in the slag And reduction failure of MnO has occurred. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. On the other hand, Ch. No. In No. 14, CaO / Al 2 O 3 in the slag was higher than 2.0. Therefore, the slag liquid phase ratio was greatly reduced, so that the fluidity of the slag was lowered, resulting in poor reduction of FeO and MnO in the slag. Oops. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. From the above results, it was confirmed that the CaO / Al 2 O 3 in the slag after steelmaking needs to be controlled in the range of 1.4 to 2.0.
Ｃｈ．Ｎｏ．１５は、スラグ中のＣａＯ／ＳｉＯ2が２．５を下回っていたため、スラグの酸化度が増加してＣによるＦｅＯおよびＭｎＯの還元不良が生じてしまった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。一方で、Ｃｈ．Ｎｏ．１６はスラグ中のＣａＯ／ＳｉＯ2が４．０を上回っていたため、スラグの初期の溶融が効率的に進行せず、スラグの流動性が低下してＦｅＯおよびＭｎＯの還元不良が生じてしまった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。以上の結果から、出鋼後のスラグ中のＣａＯ／ＳｉＯ2は２．５〜４．０の範囲に制御する必要があることが確認できた。 Ch. No. In No. 15, since CaO / SiO 2 in the slag was less than 2.5, the degree of oxidation of the slag was increased, resulting in poor reduction of FeO and MnO by C. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. On the other hand, Ch. No. In No. 16, since CaO / SiO 2 in the slag exceeded 4.0, the initial melting of the slag did not proceed efficiently, and the fluidity of the slag was lowered, resulting in poor reduction of FeO and MnO. . As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. From the above results, it was confirmed that the CaO / SiO 2 in the slag after steelmaking needs to be controlled in the range of 2.5 to 4.0.
Ｃｈ．Ｎｏ．１７は、取鍋精錬前でスラグ中のＦｅＯ濃度およびＭｎＯ濃度の合計が５質量％を下回っていたため、スラグの初期の溶融が効率的に進行せず、スラグの流動性が低下してＦｅＯおよびＭｎＯの還元不良が生じた。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。一方で、Ｃｈ．Ｎｏ．１８は取鍋精錬前でスラグ中のＦｅＯ濃度およびＭｎＯ濃度の合計が１５質量％を上回っていたため、現実的な取鍋精錬時間内にＦｅＯおよびＭｎＯを充分に還元し切れなかった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。以上の結果から、出鋼後のスラグ中のＦｅＯ濃度およびＭｎＯ濃度の合計は５〜１５質量％の範囲に制御する必要があることが確認できた。 Ch. No. No. 17, since the total of the FeO concentration and the MnO concentration in the slag before ladle refining was less than 5% by mass, the initial melting of the slag did not proceed efficiently, and the fluidity of the slag was lowered and FeO and MnO reduction failure occurred. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. On the other hand, Ch. No. Since the total of FeO concentration and MnO concentration in the slag exceeded 15% by mass before ladle refining, FeO and MnO could not be sufficiently reduced within the actual ladle refining time. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. From the above results, it was confirmed that the total of the FeO concentration and the MnO concentration in the slag after steelmaking must be controlled in the range of 5 to 15% by mass.
Ｃｈ．Ｎｏ．１９は、取鍋精錬中の雰囲気ＣＯ分圧が８０Ｔｏｒｒを超えていたため、Ｃ脱酸反応が効率的に進行せず、Ｃによるスラグ中ＦｅＯおよびＭｎＯの還元が効率的になされなかった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。以上の結果から、取鍋精錬中の雰囲気ＣＯ分圧は８０Ｔｏｒｒ未満の水準に制御する必要があることが確認できた。 Ch. No. In No. 19, since the atmospheric CO partial pressure during ladle refining exceeded 80 Torr, the C deoxidation reaction did not proceed efficiently, and the reduction of FeO and MnO in the slag by C was not efficiently performed. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. From the above results, it was confirmed that the atmospheric CO partial pressure during ladle refining needs to be controlled to a level of less than 80 Torr.
Ｃｈ．Ｎｏ．２０は、取鍋精錬中の溶鋼の攪拌動力密度が３０Ｗ／ｔｏｎを下回っていたため、溶鋼とスラグとの混合が効率的になされず、取鍋精錬処理時間内にスラグ中のＦｅＯおよびＭｎＯの還元が効率的になされなかった。その結果、脱ガス処理中にスラグからの再酸化が生じ、介在物が多く生成されてしまった。一方で、Ｃｈ．Ｎｏ．２１は、溶鋼の攪拌動力密度が８０Ｗ／ｔｏｎを上回っていたため、スラグ中のＦｅＯおよびＭｎＯを効率的に還元することができたが、取鍋の固体酸化物が損耗し、これに伴って溶鋼中で再酸化が顕著に生じてしまい脱ガス処理後の介在物個数が増加してしまった。以上の結果から、取鍋精錬中の溶鋼の攪拌動力密度は３０〜８０Ｗ／ｔｏｎの範囲内に制御する必要があることが確認できた。 Ch. No. In No. 20, since the stirring power density of the molten steel during ladle refining was less than 30 W / ton, mixing of the molten steel and slag was not efficient, and FeO and MnO in the slag were reduced within the ladle refining treatment time. Was not done efficiently. As a result, reoxidation from the slag occurred during the degassing process, and many inclusions were generated. On the other hand, Ch. No. In No. 21, since the stirring power density of the molten steel exceeded 80 W / ton, FeO and MnO in the slag could be reduced efficiently, but the solid oxide in the ladle was worn out, and accordingly the molten steel In particular, reoxidation occurred remarkably and the number of inclusions after degassing treatment increased. From the above results, it was confirmed that the stirring power density of the molten steel during ladle refining needs to be controlled within the range of 30 to 80 W / ton.
表１及び表２のＣｈ．Ｎｏ．２２〜２７は、本発明の（１）式または（２）式の条件を満たしていなかったため、発明の効果が得られなかったものである。
Ｃｈ．Ｎｏ．２２は、溶鋼中のＡｌが（１）式の範囲を超えて含有されていたため、Ａｌ脱酸がＣ脱酸よりも優勢となってＡｌ2Ｏ3が大量に生成してしまい、介在物個数が大きく増加してしまった。以上の結果から、本発明の効果を得るためには、（１）式の条件を満足する必要があることが確認できた。
In Table 1 and Table 2, Ch. No. Since Nos. 22 to 27 did not satisfy the conditions of the formula (1) or (2) of the present invention, the effects of the invention were not obtained.
Ch. No. In No. 22, since Al in the molten steel was contained exceeding the range of the formula (1), Al deoxidation was dominant over C deoxidation, and a large amount of Al 2 O 3 was produced, and the number of inclusions Has greatly increased. From the above results, it was confirmed that in order to obtain the effect of the present invention, it is necessary to satisfy the condition of the expression (1).
Ｃｈ．Ｎｏ．２３〜２７は、それぞれ取鍋精錬処理時間が（２）式の範囲から外れていたため、スラグ中のＦｅＯおよびＭｎＯが処理時間内に還元し切れず、脱ガス処理中の再酸化にて最終的な介在物個数が大きく増加してしまった。以上の結果から、本発明の効果を得るためには（２）式の条件を満足する必要があることが確認できた。 Ch. No. In Nos. 23 to 27, the ladle refining treatment time was out of the range of the formula (2), so that FeO and MnO in the slag could not be completely reduced within the treatment time, and the final reoxidation during the degassing treatment The number of inclusions has increased greatly. From the above results, it was confirmed that in order to obtain the effect of the present invention, it is necessary to satisfy the condition of the expression (2).
Claims (1)
出鋼後の溶鋼中のＡｌ濃度を（１）式の範囲に調整し、かつスラグ組成をＣａＯ／Ａｌ2Ｏ3：１．４〜２．０、ＣａＯ／ＳｉＯ2：２．５〜４．０、ＦｅＯ＋ＭｎＯ：５〜１５質量％に調整した後、前記取鍋精錬において、雰囲気ＣＯ分圧を８０Ｔｏｒｒ未満、溶鋼の攪拌動力密度を３０〜８０Ｗ／ｔｏｎに調整し、（２）式及び（３）式に示す条件で取鍋精錬処理を実施し、その後、Ａｌおよび強脱酸元素のいずれも新たに添加せずに、環流型脱ガス装置にて脱ガス処理を実施することを特徴とする清浄鋼の溶製方法。
［％Ａｌ］＜０．０３５×［％Ｃ］1.5 ・・・（１）
ｔLadle＞５５×（ＰCO／［％Ｃ］）0.28×ε-1.69×（ＷSlag／ＷSteel）1.29
・・・（２）
ε＝３７１ＧＴ／ＷSteel×｛ｌｎ（１＋７５ρSteelＨ／ＰLadle）＋０．０６（１−３００／Ｔ）｝ ・・・（３）
ここで、［％Ａｌ］：溶鋼中Ｓｏｌ．Ａｌ濃度（質量％）、［％Ｃ］：溶鋼中Ｃ濃度（質量％）、ｔLadle：取鍋精錬処理時間（ｍｉｎ）、ＰCO：取鍋内ＣＯ分圧（Ｔｏｒｒ）、ε：攪拌動力密度（Ｗ／ｔｏｎ）、ＷSlag：スラグ質量（ｋｇ）、ＷSteel：溶鋼質量（ｔｏｎ）、Ｇ：底吹き不活性ガス流量（Ｎｍ3／ｓ）、Ｔ：溶鋼温度（Ｋ）、ρSteel：溶鋼密度（ｔｏｎ／ｍ3）、Ｈ：取鍋内溶鋼の浴深（ｍ）、ＰLadle：取鍋内全圧（Ｔｏｒｒ）である。 C: 0.2-1.2% by mass, Si: 0.03-0.3% by mass, Mn: 0.1-1.5% by mass, Ti: 0.03% by mass or less containing molten steel, After carrying out ladle refining under bottom blowing stirring with inert gas, it is a method for producing clean steel in which degassing treatment is performed with a reflux degassing device,
The Al concentration in the molten steel after steel is adjusted to the range of the formula (1), and the slag composition is CaO / Al 2 O 3 : 1.4 to 2.0, CaO / SiO 2 : 2.5 to 4 . After adjusting to 0, FeO + MnO: 5 to 15% by mass, in the ladle refining, the atmospheric CO partial pressure is adjusted to less than 80 Torr, and the stirring power density of the molten steel is adjusted to 30 to 80 W / ton. ) The ladle refining process is carried out under the conditions shown in the formula, and then the degassing process is carried out in a recirculation type degassing apparatus without newly adding any of Al and strong deoxidizing elements. A method for melting clean steel.
[% Al] <0.035 × [% C] 1.5 (1)
t Ladle > 55 × (P CO / [% C]) 0.28 × ε- 1.69 × (W Slag / W Steel ) 1.29
... (2)
ε = 371 GT / W Steel × {ln (1 + 75ρ Steel H / P Ladle ) +0.06 (1-300 / T)} (3)
Here, [% Al]: Sol. Al concentration (% by mass), [% C]: C concentration in molten steel (% by mass), t Ladle : Ladle refining treatment time (min), P CO : CO partial pressure in the ladle (Torr), ε: Stirring power Density (W / ton), W Slag : Slag mass (kg), W Steel : Molten steel mass (ton), G: Bottom blowing inert gas flow rate (Nm 3 / s), T: Molten steel temperature (K), ρ Steel : Molten steel density (ton / m 3 ), H: Bath depth (m) of molten steel in the ladle, P Ladle : Total pressure in the ladle (Torr).
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| JP2020180341A (en) * | 2019-04-25 | 2020-11-05 | 日本製鉄株式会社 | Melting method of ultra-low nitrogen steel |
| CN112030067A (en) * | 2020-07-23 | 2020-12-04 | 江苏华能电缆股份有限公司 | Ultrahigh-strength armored steel wire for load-bearing exploration cable and manufacturing method thereof |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008303406A (en) * | 2007-06-05 | 2008-12-18 | Kobe Steel Ltd | Method for manufacturing high-cleanliness steel |
| JP2012172218A (en) * | 2011-02-23 | 2012-09-10 | Sumitomo Metal Ind Ltd | Method of melting low-al steel |
| JP2015161022A (en) * | 2014-02-28 | 2015-09-07 | 新日鐵住金株式会社 | Method for smelting highly clean steel |
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| JP2015161022A (en) * | 2014-02-28 | 2015-09-07 | 新日鐵住金株式会社 | Method for smelting highly clean steel |
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| JP2020180341A (en) * | 2019-04-25 | 2020-11-05 | 日本製鉄株式会社 | Melting method of ultra-low nitrogen steel |
| JP7265136B2 (en) | 2019-04-25 | 2023-04-26 | 日本製鉄株式会社 | Melting method of ultra-low nitrogen steel |
| CN112030067A (en) * | 2020-07-23 | 2020-12-04 | 江苏华能电缆股份有限公司 | Ultrahigh-strength armored steel wire for load-bearing exploration cable and manufacturing method thereof |
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