JP6414098B2 - Melting method of high Si high Al ultra-low carbon steel - Google Patents
Melting method of high Si high Al ultra-low carbon steel Download PDFInfo
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本発明は、極低炭素鋼でありながらSiとAlを多量に含有する高Si高Al極低炭素鋼の溶製方法に関するものである。 The present invention relates to a method for melting a high-Si high-Al ultra-low carbon steel containing a large amount of Si and Al while being an ultra-low carbon steel.
製鋼工程において、溶鋼の輸送手段として取鍋が使用されている。そして近年では、取鍋を、輸送手段としてのみならず、溶鋼の精錬に関わる反応容器としても使用する技術が開発されている。取鍋を反応容器として使用する場合は、所定の反応が終了するまで溶鋼を取鍋内に収容する必要がある。そのため溶鋼が取鍋内に長時間にわたって収容されることになるので、取鍋に内張りされる耐火煉瓦は耐摩耗性、耐スポーリング性に優れた材料が使用され、特に、溶鋼上のスラグが接触する位置の耐火煉瓦（以下、スラグライン煉瓦という）はMgO、Cを主成分とする耐火煉瓦が使用されている。 In the steelmaking process, a ladle is used as a means for transporting molten steel. In recent years, a technique has been developed in which a ladle is used not only as a transportation means but also as a reaction vessel for refining molten steel. When using a ladle as a reaction container, it is necessary to accommodate molten steel in a ladle until a predetermined reaction is completed. Therefore, the molten steel will be stored in the ladle for a long time, so the refractory bricks lined in the ladle are made of materials with excellent wear resistance and spalling resistance. Refractory bricks mainly composed of MgO and C are used for the refractory bricks in contact (hereinafter referred to as slag line bricks).
こうして溶製した溶鋼から鋼板が製造され、様々な用途に使用される。たとえば自動車外装用鋼板や缶用鋼板等の分野では、Cの含有量が0.01質量％以下の極低炭素鋼と呼ばれる鋼板が広く使用されており、製鋼工程における溶鋼のC含有量を効率良く、かつ精度良く0.01質量％以下まで低減する技術が開発されている。 Steel plates are produced from the molten steel thus produced and used for various purposes. For example, in the field of steel sheets for car exteriors and steel sheets for cans, steel sheets called ultra-low carbon steel with a C content of 0.01% by mass or less are widely used, and the C content of molten steel in the steelmaking process is efficiently increased. In addition, technology has been developed that accurately reduces it to 0.01% by mass or less.
一方で、自動車の排ガスが原因となる環境汚染や地球温暖化を防止するために、電気モーターで走行する自動車（たとえば電気自動車、ハイブリッド車等）が開発され、実用化の段階に来ている。電気モーターの材料として、従来から、SiとAlを多量に含有する鋼板（いわゆる電磁鋼板）が使用されているが、電気モーターの効率や出力を更に向上するために、高Si高AlでありかつC含有量を極低炭素鋼のレベルまで低減した鋼板を製造する技術が種々検討されている。 On the other hand, in order to prevent environmental pollution and global warming caused by exhaust gas from automobiles, automobiles that run on electric motors (for example, electric cars, hybrid cars, etc.) have been developed and are in the stage of practical use. Conventionally, steel plates containing so much Si and Al (so-called electromagnetic steel plates) have been used as materials for electric motors, but in order to further improve the efficiency and output of electric motors, Various techniques for producing steel sheets with a C content reduced to the level of ultra-low carbon steel have been studied.
たとえば特許文献１には、ＲＨ真空脱ガス処理において、取鍋内の溶鋼のO含有量とC含有量との比を制御することによって、C含有量を極低炭素鋼のレベルまで低下する技術が開示されている。 For example, Patent Document 1 discloses a technique for reducing the C content to the level of extremely low carbon steel by controlling the ratio of the O content and the C content of the molten steel in the ladle in the RH vacuum degassing process. Is disclosed.
しかしながらMgO、Cを主成分とする耐火煉瓦をスラグライン煉瓦として使用する取鍋では、溶鋼のC含有量を低下させても、その後の連続鋳造に至るまで溶鋼が取鍋内に収容される間に、スラグライン煉瓦からCが溶出して、溶鋼のC含有量が上昇するので、極低炭素鋼を安定して溶製するのが困難であるという問題がある。 However, in ladles that use refractory bricks composed mainly of MgO and C as slag line bricks, even if the C content of the molten steel is reduced, the molten steel is stored in the ladle until the subsequent continuous casting. In addition, C is eluted from the slag line brick and the C content of the molten steel is increased, so that there is a problem that it is difficult to stably melt extremely low carbon steel.
特許文献２には、取鍋に収容した溶鋼上のスラグ（以下、取鍋スラグという）のCaO含有量とSiO2含有量との比（いわゆる塩基度）、ならびにMgO含有量を制御することによって、スラグライン煉瓦を取鍋スラグでコーティングして、Cの溶出を防止する技術が開示されている。 In Patent Document 2, by controlling the ratio (so-called basicity) of CaO content and SiO 2 content of slag on molten steel (hereinafter referred to as ladle slag) contained in a ladle, and MgO content. A technique is disclosed in which slag line bricks are coated with pan slag to prevent the dissolution of C.
しかしながら極低炭素鋼の電磁鋼板の溶製においては、O含有量が400ppm程度の溶鋼を転炉から出鋼し、次いでＲＨ真空脱ガス処理でC含有量を極低炭素鋼のレベルまで低下させた後、真空槽の上部から多量のSiとAlを投入するので、そのSiと溶鋼中のOとが反応し、生成されたSiO2が取鍋スラグに混入する。その結果、取鍋スラグのSiO2含有量が上昇し、取鍋スラグの融点の上昇および粘度の上昇をもたらす。したがって、特許文献２に開示されるような成分の取鍋スラグでは、取鍋の鉄皮や耐火煉瓦、あるいは真空槽に取付けられる浸漬管に取鍋スラグが大量に付着して、ＲＨ真空脱ガス装置の操業に支障を来たすばかりでなく、取鍋ならびに浸漬管の寿命低下を引き起こす。 However, in the melting of electrical steel sheets with extremely low carbon steel, molten steel with an O content of about 400 ppm is removed from the converter, and then the C content is reduced to the level of extremely low carbon steel by RH vacuum degassing. After that, since a large amount of Si and Al are introduced from the upper part of the vacuum chamber, the Si reacts with O in the molten steel, and the generated SiO 2 is mixed into the ladle slag. As a result, the content of SiO 2 in the ladle slag increases, resulting in an increase in the melting point and viscosity of the ladle slag. Therefore, in the ladle slag of the component as disclosed in Patent Document 2, a large amount of ladle slag adheres to a ladder pipe or a refractory brick, or a dip tube attached to a vacuum tank, and RH vacuum degassing. Not only will the operation of the equipment be hindered, but also the life of the ladle and dip tube will be reduced.
取鍋スラグのMgO含有量が高い場合も、取鍋あるいは浸漬管に取鍋スラグが付着し易くなる。したがって、取鍋スラグのMgO含有量は低い方が好ましい。
また、電磁鋼板の溶製においては、真空槽の上部から多量のSiとAlを投入するので、溶鋼中にSiO2およびAl2O3が生成される。これらの酸化物の生成反応は、いずれも発熱反応であるから、溶鋼の温度が上昇する。したがって、電磁鋼板の素材となる溶鋼が転炉から出鋼される時の温度は、一般的な溶鋼の出鋼温度よりも低く設定されている。そのためＲＨ真空脱ガス処理では、融点が高温である取鍋スラグは溶融し難くなる。
Even when the MgO content of the ladle slag is high, the ladle slag tends to adhere to the ladle or the dip tube. Therefore, it is preferable that the ladle slag has a low MgO content.
Further, in the melting of electromagnetic steel sheets, a large amount of Si and Al are introduced from the upper part of the vacuum chamber, so that SiO 2 and Al 2 O 3 are generated in the molten steel. Since all of these oxide formation reactions are exothermic reactions, the temperature of the molten steel rises. Therefore, the temperature at which the molten steel used as the material of the electromagnetic steel sheet is discharged from the converter is set lower than the temperature at which the general molten steel is discharged. Therefore, in the RH vacuum degassing process, ladle slag having a high melting point is difficult to melt.
特許文献２に開示されたような取鍋スラグは融点が高いので、同様の成分を有する取鍋スラグが極低炭素鋼の電磁鋼板の真空脱ガス処理にて生成すると、ＲＨ真空脱ガス装置の操業に悪影響を及ぼす。 Since the ladle slag as disclosed in Patent Document 2 has a high melting point, when ladle slag having the same component is generated by vacuum degassing treatment of an electromagnetic steel sheet of ultra-low carbon steel, the RH vacuum degassing apparatus It will adversely affect operations.
本発明は、従来の技術の問題点を解消し、極低炭素鋼でありながらSiとAlを多量に含有する高Si高Al極低炭素鋼を溶製する際に、ＲＨ真空脱ガス処理の進行中のみならず、終了後（すなわち連続鋳造を行なうまでの間）も、取鍋スラグによるスラグライン煉瓦のコーティングの効果を得て、スラグライン煉瓦の溶損を防止し、かつスラグライン煉瓦からCが溶出するのを防止することが可能な取鍋スラグを生成させ、しかも、その取鍋スラグの融点および粘度の上昇を抑制することによって、高Si高Al極低炭素鋼を効率良く安定して溶製できる溶製方法を提供することを目的とする。 The present invention eliminates the problems of the prior art, and when melting high Si high Al ultra-low carbon steel containing a large amount of Si and Al while being ultra-low carbon steel, the RH vacuum degassing treatment is performed. Not only during the process, but also after the end (that is, until continuous casting), the effect of coating the slag line brick with ladle slag is obtained to prevent the slag line brick from being melted and from the slag line brick. By producing ladle slag capable of preventing C from eluting and suppressing the rise in melting point and viscosity of the ladle slag, high Si high Al ultra-low carbon steel can be stabilized efficiently. An object of the present invention is to provide a melting method that can be melted.
本発明者は、従来の高Si高Al極低炭素鋼の真空脱ガス処理では高融点かつ高粘度の取鍋スラグが生成することから、取鍋スラグの成分が融点や粘度に及ぼす影響について検討した。そして、取鍋スラグのMgO含有量を適正に制御することによって、低温の溶鋼を取鍋に収容して真空脱ガス処理を行なう際に、取鍋スラグでスラグライン煉瓦を十分にコーティングすることが可能であり、しかも取鍋スラグが取鍋や浸漬管に付着するのを防止できることを見出した。 The present inventor examines the influence of ladle slag components on melting point and viscosity because the high-melting and high-viscosity ladle slag is produced by vacuum degassing of conventional high-Si high-Al ultra-low carbon steel. did. And by appropriately controlling the MgO content of the ladle slag, when ladle the low temperature molten steel in the ladle and perform vacuum degassing treatment, the ladle line slag can be sufficiently coated with the slag line brick It was found that the ladle slag can be prevented from adhering to the ladle or the dip tube.
本発明は、このような知見に基づいてなされたものである。
すなわち本発明は、転炉にて脱炭吹錬を施した溶鋼を、スラグライン煉瓦としてMgO、Cを主成分とする耐火煉瓦を使用した取鍋に収容し、取鍋内の取鍋スラグにMgOを投入して取鍋スラグのMgO含有量を７〜10質量％に調整した後、ＲＨ真空脱ガス装置を用いて溶鋼に真空脱ガス処理を施して、C：0.0010質量％以下、Si：2.0〜3.0質量％、Mn：1.0〜2.0質量％、P：0.05質量％以下、S：0.02質量％以下、Al：0.4〜1.2質量％を含有する高Si高Al極低炭素鋼を得る溶製方法である。
The present invention has been made based on such knowledge.
That is, the present invention accommodates molten steel that has been decarburized and blown in a converter in a ladle that uses refractory bricks mainly composed of MgO and C as slag line bricks, and the ladle slag in the ladle. After MgO was added and the MgO content of the ladle slag was adjusted to 7 to 10% by mass, the molten steel was vacuum degassed using an RH vacuum degasser, and C: 0.0010% by mass or less, Si: Melting to obtain high Si high Al ultra-low carbon steel containing 2.0-3.0 mass%, Mn: 1.0-2.0 mass%, P: 0.05 mass% or less, S: 0.02 mass% or less, Al: 0.4-1.2 mass% Is the method.
本発明の高Si高Al極低炭素鋼の溶製方法においては、スラグライン煉瓦が、MgO：77〜79質量％、C：13〜14質量％を含有することが好ましい。また、取鍋スラグに投入するMgO源は取鍋スラグ１トンあたり0.1〜0.2トンであることが好ましい。 In the melting method of the high Si high Al ultra-low carbon steel of the present invention, the slag line brick preferably contains MgO: 77 to 79% by mass and C: 13 to 14% by mass. Moreover, it is preferable that the MgO source thrown into the ladle slag is 0.1 to 0.2 ton per ton of ladle slag.
本発明によれば、高Si高Al極低炭素鋼を効率良く安定して溶製することが可能となり、産業上格段の効果を奏する。 ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to smelt high Si high Al ultra-low carbon steel efficiently and stably, and there exists a remarkable industrial effect.
一般に製鉄工場の製銑工程から製鋼工程へ至る過程で、高炉から出銑した溶銑を搬送容器（たとえばトーピードカー、溶銑鍋等）に収容して、保温しつつ転炉へ輸送する。そして、輸送しながら溶銑に対して予備処理（たとえば予備脱燐処理、予備脱硫処理等）を施した後、溶銑を転炉に装入して、上吹き酸素あるいは底吹き酸素によって脱炭吹錬を行なって溶鋼を得る。 In general, in the process from a steelmaking process to a steelmaking process in an iron factory, hot metal discharged from a blast furnace is accommodated in a transport container (for example, a torpedo car, a hot metal ladle, etc.) and transported to a converter while keeping the temperature. And after carrying out preliminary treatment (for example, preliminary dephosphorization treatment, preliminary desulfurization treatment, etc.) to the hot metal while transporting, the hot metal is charged into the converter and decarburized and blown by top blowing oxygen or bottom blowing oxygen. To obtain molten steel.
高Si高Al極低炭素鋼を溶製するにあたって、転炉内の溶鋼のC含有量が0.02質量％未満になるまで脱炭吹錬を行なった場合は、溶鋼中のFe、MnがFeO、MnO等の低級酸化物となって、転炉内のスラグ（以下、転炉スラグという）に吸着するので、FeやMnの歩留りの低下を招く。溶鋼のC含有量が0.06質量％を超える状態で脱炭吹錬を停止した場合は、次工程のＲＨ真空脱ガス装置で脱炭するのに長時間を要するので、生産性の低下を引き起こす。したがって、転炉から出鋼する溶鋼のC含有量は0.02〜0.06質量％の範囲内が好ましい。 When melting high Si high Al ultra-low carbon steel, when decarburization blown until the C content of the molten steel in the converter is less than 0.02% by mass, Fe and Mn in the molten steel are FeO, Since it becomes a lower oxide such as MnO and is adsorbed on the slag in the converter (hereinafter referred to as converter slag), the yield of Fe and Mn is reduced. When decarburization blowing is stopped in a state where the C content of the molten steel exceeds 0.06% by mass, it takes a long time to decarburize with the RH vacuum degassing apparatus in the next step, which causes a decrease in productivity. Therefore, the C content of the molten steel coming out from the converter is preferably in the range of 0.02 to 0.06 mass%.
転炉から出鋼された溶鋼のO含有量が400ppm未満の場合は、次工程の真空脱ガス装置にて真空槽で投入される成分調整用のSi、Alと溶鋼中の溶存Oとの酸化反応が進行せず、十分な反応熱が発生しない。そのため、真空槽の上部からO2ガスを吹付けるとともに、酸化発熱量の大きい金属（たとえばAl等）を投入して溶鋼の温度を上昇させなければならないので、通常の温度調整処理よりも長時間を要する。溶鋼のO含有量が600ppmを超える場合は、溶鋼の密度が小さくなり、真空槽内で溶鋼が円滑に流れなくなる。また、真空槽内で溶鋼が許容される高さを上回る位置まで上昇して、設備故障（たとえばSiやAlの投入口の閉塞等）を引き起こす。したがって、転炉から出鋼する溶鋼のO含有量は400〜600ppmの範囲内が好ましい。 When the O content of the molten steel produced from the converter is less than 400 ppm, oxidation of Si, Al for component adjustment and dissolved O in the molten steel is introduced in the vacuum tank in the vacuum degassing unit in the next process. The reaction does not proceed and sufficient heat of reaction is not generated. For this reason, it is necessary to blow O 2 gas from the top of the vacuum chamber and increase the temperature of the molten steel by introducing a metal with a large amount of oxidation heat (such as Al). Cost. When the O content of the molten steel exceeds 600 ppm, the density of the molten steel becomes small and the molten steel does not flow smoothly in the vacuum chamber. Moreover, it raises to the position where the molten steel exceeds the allowable height in the vacuum chamber, causing equipment failure (for example, blocking of the inlet of Si or Al). Therefore, the O content of the molten steel coming out of the converter is preferably in the range of 400 to 600 ppm.
脱炭吹錬が終了した後、転炉から溶鋼を取鍋に出鋼する。出鋼時の溶鋼の温度は、1560〜1620℃の範囲内が好ましい。この温度は通常の出鋼温度よりも50〜100℃程度低く設定した温度であり、次工程のＲＨ真空脱ガス装置で真空脱ガス処理を行なうことによって、SiO2やAl2O3が生成する発熱反応が進行することを考慮して設定された温度である。 After decarburization blowing is finished, the molten steel is taken out from the converter into a ladle. The temperature of the molten steel at the time of steel output is preferably in the range of 1560 to 1620 ° C. This temperature is set to about 50 to 100 ° C. lower than the normal steel output temperature, and SiO 2 and Al 2 O 3 are generated by performing vacuum degassing with the RH vacuum degassing apparatus in the next step. The temperature is set in consideration of the progress of the exothermic reaction.
転炉から出鋼する際には、溶鋼とともに転炉スラグ（MgO含有量５〜６質量％程度）の一部が取鍋に流出する。その結果、取鍋に流出した一部の転炉スラグ（以下、取鍋スラグという）が、取鍋内の溶鋼上に滞留する。その取鍋スラグにMgOを投入して、取鍋スラグのMgO含有量を７〜10質量％に調整する。ここで投入するのはMgOを含有する物質（いわゆるMgO源）であれば良く、MgO源の投入量は取鍋スラグ１トンあたり0.1〜0.2トンであることが好ましい。このMgO源の投入量をMgOの投入量に換算すると、0.03〜0.08トンに相当する。 When steel is output from the converter, a part of the converter slag (MgO content of about 5 to 6% by mass) flows out into the ladle along with the molten steel. As a result, some converter slag (hereinafter referred to as ladle slag) that has flowed into the ladle stays on the molten steel in the ladle. MgO is put into the ladle slag, and the MgO content of the ladle slag is adjusted to 7 to 10% by mass. The material to be added here may be a material containing MgO (so-called MgO source), and the amount of the MgO source input is preferably 0.1 to 0.2 ton per ton of ladle slag. When the input amount of the MgO source is converted into the input amount of MgO, it corresponds to 0.03 to 0.08 tons.
取鍋スラグのMgO含有量の調整とともに、極低炭素鋼を溶製する際に施される従来のスラグ改質を行なっても良い。また、取鍋スラグの酸素ポテンシャルが高い場合は、FeOやMnO等の低級酸化物の生成を抑制するために脱酸剤を投入して、取鍋スラグの酸素ポテンシャルを低下させても良い。 In addition to adjusting the MgO content of the ladle slag, conventional slag reforming performed when melting ultra-low carbon steel may be performed. In addition, when the oxygen potential of the ladle slag is high, a deoxidizer may be added to suppress the formation of lower oxides such as FeO and MnO to lower the oxygen potential of the ladle slag.
取鍋スラグのMgO含有量の調整が終了した後、取鍋をＲＨ真空脱ガス装置へ搬送して、取鍋内の溶鋼に真空脱ガス処理を行なう。ここで、真空脱ガス処理の手順について説明する。 After the adjustment of the MgO content of the ladle slag is completed, the ladle is transported to the RH vacuum degasser, and the molten steel in the ladle is vacuum degassed. Here, the procedure of the vacuum degassing process will be described.
真空脱ガス処理を行なうにあたって、まず、昇降装置で取鍋を上昇させ、真空槽の下部に取付けた２本の浸漬管を取鍋内の溶鋼に浸漬する。次いで、真空槽の上部の排気口に連結された真空排気装置で真空槽内を減圧する。それと同時に、片方の浸漬管に取付けた金属製の送風管（いわゆるステンパイプ）から環流用Arガスを吹込んで、ガスリフト効果によって取鍋内の溶鋼を真空槽内へ環流させる。 In carrying out the vacuum degassing treatment, first, the ladle is raised by the lifting device, and the two dip tubes attached to the lower part of the vacuum chamber are immersed in the molten steel in the ladle. Next, the inside of the vacuum chamber is depressurized by a vacuum exhaust device connected to the exhaust port at the top of the vacuum chamber. At the same time, Ar gas for recirculation is blown from a metal blower pipe (so-called stainless pipe) attached to one of the dip tubes, and the molten steel in the ladle is recirculated into the vacuum chamber by the gas lift effect.
真空槽内は大気中よりCO分圧が低いので、真空槽内で溶鋼中のCと溶存Oとの反応が進行する。つまり脱炭反応が進行して、溶鋼中のCがCOとなって排気口を通じて排気される。このようにして極低炭素鋼を溶製することができる。真空脱ガス処理によって溶存Oが減少して、脱炭反応が遅延する場合には、真空槽の上部に取付けたランスからO2ガスを吹込むことによって、脱炭反応を促進することが可能である。 Since the CO partial pressure is lower in the vacuum chamber than in the atmosphere, the reaction between C in the molten steel and dissolved O proceeds in the vacuum chamber. In other words, the decarburization reaction proceeds, and C in the molten steel becomes CO and is exhausted through the exhaust port. In this way, ultra-low carbon steel can be melted. When the decarburization reaction is delayed due to a decrease in dissolved O due to the vacuum degassing treatment, it is possible to accelerate the decarburization reaction by blowing O 2 gas from a lance attached to the top of the vacuum chamber. is there.
こうして溶鋼を環流させながら、脱炭反応を伴う真空脱ガス処理を行なって、溶鋼のC含有量が所定の規定値に達したとき、真空槽の上部に取付けたホッパーから成分調整用のSiとAlを投入する。SiとAlは脱酸剤としての機能も有する。ここで投入するのはSi、Alを含有する物質（たとえばSi系合金、Al系合金等）であれば良い。ただし、SiよりもAlを先に投入すると、溶鋼中の溶存Oと投入されたAlとが反応して、溶鋼中に多量のAl2O3が生成し、後工程の連続鋳造の操業に支障をきたす。したがって、先にSiを投入し、次にAlを投入することが好ましい。 While circulating the molten steel, vacuum degassing treatment with decarburization reaction was performed, and when the C content of the molten steel reached a predetermined specified value, the component adjustment Si and Si were adjusted from the hopper attached to the upper part of the vacuum tank. Insert Al. Si and Al also have a function as a deoxidizer. Here, it is sufficient to use a substance containing Si or Al (for example, Si-based alloy, Al-based alloy, etc.). However, if Al is added before Si, the dissolved O in the molten steel reacts with the introduced Al, and a large amount of Al 2 O 3 is generated in the molten steel, hindering continuous casting operations in the subsequent process. Bring Therefore, it is preferable to introduce Si first and then Al.
SiとAlを投入した後、溶鋼の環流を数分間継続して、その間に真空槽の上部のホッパーから成分調整用のMnを投入する。ここで投入するのはMnを含有する物質（たとえばMn系合金等）であれば良い。
そして、溶鋼の環流を停止して、真空脱ガス処理を終了する。その後、取鍋は連続鋳造設備へ搬送される。
After introducing Si and Al, the molten steel is continuously refluxed for several minutes, while Mn for adjusting the components is introduced from the hopper at the top of the vacuum chamber. What is necessary here is to use a substance containing Mn (for example, an Mn alloy).
And the reflux of molten steel is stopped and a vacuum degassing process is complete | finished. Thereafter, the ladle is transferred to a continuous casting facility.
このような手順で真空脱ガス処理を行なう間に、投入されたSiと溶鋼中の溶存Oとが反応して、真空槽内の溶鋼中に大量のSiO2が発生する。そして溶鋼の環流によって、そのSiO2が取鍋へ移動して取鍋スラグに吸着する。その結果、取鍋スラグのSiO2が増加して、塩基度が1.0〜1.5と非常に低い値を示し、スラグライン煉瓦に付着し易い取鍋スラグが生成される。なお塩基度は、SiO2の含有量（これを[SiO2]と記す）とCaOの含有量（これを[CaO]と記す）とを用いて、[CaO]／[SiO2]で算出される値である。 During the vacuum degassing process in such a procedure, the charged Si reacts with the dissolved O in the molten steel, and a large amount of SiO 2 is generated in the molten steel in the vacuum chamber. And by the recirculation of molten steel, the SiO 2 moves to the ladle and is adsorbed on the ladle slag. As a result, the ladle slag has an increased SiO 2 and a basicity of 1.0 to 1.5, which is a very low value, and ladle slag that easily adheres to the slag line brick is generated. Note basicity, the content of SiO 2 (this is referred to as [SiO 2]) and the content of CaO by using the (this referred to as [CaO]), calculated in [CaO] / [SiO 2] Value.
また、投入されたAlの一部が溶鋼中の溶存Oや取鍋スラグ中の低級酸化物と反応してAl2O3となり、取鍋スラグに吸着する。その結果、取鍋スラグの融点が低下して、スラグライン煉瓦に付着し易くなる。 Moreover, a part of the charged Al reacts with dissolved O in the molten steel and lower oxide in the ladle slag to become Al 2 O 3 and is adsorbed on the ladle slag. As a result, the melting point of the ladle slag is lowered and it becomes easy to adhere to the slag line brick.
以上に説明した通り、真空脱ガス処理を行なう過程で取鍋スラグがスラグライン煉瓦をコーティングして、ＲＨ真空脱ガス処理の進行中のみならず終了後も、スラグライン煉瓦の溶損を防止し、Cの溶出を防止する。しかも、取鍋スラグがスラグライン煉瓦に付着し易い環境（すなわち取鍋内の溶鋼の温度が低く、かつ取鍋スラグの塩基度が低い環境）の中で、スラグライン煉瓦の過剰なコーティングを回避できる成分の取鍋スラグを生成することによって、高Si高Al極低炭素鋼を効率良く安定して溶製することができる。 As explained above, ladle slag coats slag line bricks in the process of vacuum degassing treatment, preventing slag line bricks from being damaged not only during RH vacuum degassing treatment but also after completion. , Prevent elution of C. In addition, avoiding excessive coating of slag line bricks in an environment where ladle slag tends to adhere to slag line bricks (ie, the temperature of the molten steel in the ladle is low and the basicity of ladle slag is low). By producing ladle slag with possible components, high Si high Al ultra-low carbon steel can be efficiently and stably melted.
なお本発明の溶製方法は、C：0.0010質量％以下、Si：2.0〜3.0質量％、Mn：1.0〜2.0質量％、P：0.05質量％以下、S：0.02質量％以下、Al：0.4〜1.2質量％を含有する高Si高Al極低炭素鋼に適用することによって、顕著な効果が得られる。 The melting method of the present invention is as follows: C: 0.0010 mass% or less, Si: 2.0 to 3.0 mass%, Mn: 1.0 to 2.0 mass%, P: 0.05 mass% or less, S: 0.02 mass% or less, Al: 0.4 to By applying to high Si high Al ultra-low carbon steel containing 1.2% by mass, a remarkable effect can be obtained.
また、MgO：77〜79質量％、C：13〜14質量％を含有するスラグライン煉瓦を使用することによって、その効果が安定してもたらされる。 Moreover, the effect is brought about stably by using the slag line brick containing MgO: 77-79 mass% and C: 13-14 mass%.
高炉から出銑された溶銑をトーピードカーで受銑して搬送し、その溶銑をトーピードカーから転炉装入鍋に移した。そして、転炉装入鍋にCaO系脱硫剤を添加するとともに、回転する攪拌羽根を溶銑に浸漬し、溶銑とCaO系脱硫剤を攪拌して溶銑予備処理を行なった。引き続き、溶銑を転炉に装入して、溶銑の脱炭吹錬を施し、得られた溶鋼を取鍋に出鋼した。転炉出鋼時の溶鋼のC含有量は0.03質量％、SiとAlは微量（いわゆるトレース）であり、溶鋼の温度は1592℃であった。 The hot metal discharged from the blast furnace was received and conveyed by a torpedo car, and the hot metal was transferred from the torpedo car to the converter charging pan. And while adding the CaO type | system | group desulfurization agent to a converter charging pan, the rotating stirring blade was immersed in hot metal, the hot metal and the CaO type desulfurization agent were stirred, and the hot metal preliminary process was performed. Subsequently, the hot metal was charged into a converter and subjected to decarburization blowing of the hot metal, and the resulting molten steel was taken out into a ladle. The C content of the molten steel at the time of converter steelmaking was 0.03% by mass, the amounts of Si and Al were very small (so-called traces), and the temperature of the molten steel was 1592 ° C.
次に、取鍋内の溶鋼に、MgO源であるスラグ改質剤を手投げで0.145トン投入した。このMgO源の投入量は、MgOの投入量に換算して、取鍋スラグ１トンあたり0.05トンに相当する。
そして、ＲＨ真空脱ガス装置へ搬送して真空脱ガス処理を施した。真空脱ガス処理が終了した後の取鍋スラグのT.Feは3.3質量％、Al2O3は20.3質量％、MgOは7.7質量％、MnOは4.0質量％、塩基度[CaO]／[SiO2]は1.2となり、目標とした許容範囲を満たしていた。また、真空脱ガス処理が終了した後の溶鋼のC含有量は0.0003質量％であった。
Next, 0.145 tons of slag modifier as a MgO source was thrown into the molten steel in the ladle by hand. The input amount of this MgO source is equivalent to 0.05 tons per ton of ladle slag in terms of the input amount of MgO.
And it conveyed to RH vacuum degassing apparatus and performed the vacuum degassing process. After the vacuum degassing treatment, the ladle slag T.Fe is 3.3% by mass, Al 2 O 3 is 20.3% by mass, MgO is 7.7% by mass, MnO is 4.0% by mass, basicity [CaO] / [SiO 2 ] was 1.2, which met the target tolerance. Further, the C content of the molten steel after the vacuum degassing treatment was 0.0003% by mass.
その後、連続鋳造を行なって、鋳片のC含有量を測定したところ、0.00033質量％であった。つまり、C含有量の上昇量は0.00003質量％であり、極めて低く抑えられた。
なお、この鋳片のC含有量（＝0.00033質量％）は、製造工程で許容される上限0.0004質量％に対して、その上限を超えることなく溶鋼を溶製できたことを示している。
Thereafter, continuous casting was performed, and the C content of the slab was measured. As a result, it was 0.00033% by mass. In other words, the increase in the C content was 0.00003% by mass, which was extremely low.
The C content (= 0.00033 mass%) of the slab indicates that the molten steel could be melted without exceeding the upper limit of 0.0004 mass% allowed in the manufacturing process.
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