JP5910579B2 - Melting method of ultra-low nitrogen pure iron - Google Patents
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims description 179
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims description 110
- 229910052757 nitrogen Inorganic materials 0.000 title claims description 90
- 229910052742 iron Inorganic materials 0.000 title claims description 54
- 238000000034 method Methods 0.000 title claims description 30
- 238000002844 melting Methods 0.000 title claims description 25
- 230000008018 melting Effects 0.000 title claims description 25
- 229910000831 Steel Inorganic materials 0.000 claims description 161
- 239000010959 steel Substances 0.000 claims description 161
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 62
- 229910052799 carbon Inorganic materials 0.000 claims description 62
- 238000007670 refining Methods 0.000 claims description 50
- 238000005261 decarburization Methods 0.000 claims description 47
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 28
- 229910052698 phosphorus Inorganic materials 0.000 claims description 28
- 239000011574 phosphorus Substances 0.000 claims description 28
- 238000009849 vacuum degassing Methods 0.000 claims description 24
- 229910052751 metal Inorganic materials 0.000 claims description 22
- 239000002184 metal Substances 0.000 claims description 22
- 238000006243 chemical reaction Methods 0.000 claims description 21
- 239000007789 gas Substances 0.000 claims description 17
- 239000003610 charcoal Substances 0.000 claims description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 11
- 229910052760 oxygen Inorganic materials 0.000 description 11
- 239000001301 oxygen Substances 0.000 description 11
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 8
- 238000005255 carburizing Methods 0.000 description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 7
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 7
- 239000003795 chemical substances by application Substances 0.000 description 7
- 238000006477 desulfuration reaction Methods 0.000 description 7
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- 238000007664 blowing Methods 0.000 description 6
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- 239000000292 calcium oxide Substances 0.000 description 4
- 235000012255 calcium oxide Nutrition 0.000 description 4
- 239000006229 carbon black Substances 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000007800 oxidant agent Substances 0.000 description 4
- 239000010936 titanium Substances 0.000 description 4
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 3
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 229910001882 dioxygen Inorganic materials 0.000 description 3
- 230000006698 induction Effects 0.000 description 3
- 229910052748 manganese Inorganic materials 0.000 description 3
- 239000011572 manganese Substances 0.000 description 3
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 238000010309 melting process Methods 0.000 description 3
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- 239000002893 slag Substances 0.000 description 3
- 238000009628 steelmaking Methods 0.000 description 3
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- 229910052719 titanium Inorganic materials 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 230000000903 blocking effect Effects 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
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- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
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- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- 229910000677 High-carbon steel Inorganic materials 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 238000010306 acid treatment Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 150000001721 carbon Chemical class 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- 239000000571 coke Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 150000002505 iron Chemical class 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
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- 238000005507 spraying Methods 0.000 description 1
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Description
本発明は、転炉での精錬とＲＨ真空脱ガス装置での精錬とを組み合わせて、窒素含有量の少ない純鉄を溶製する方法に関する。 The present invention relates to a method for melting pure iron having a low nitrogen content by combining refining in a converter and refining in an RH vacuum degassing apparatus.
純鉄（「工業用純鉄」ともいう）は、炭素、珪素、マンガンなどの不純物の含有量が少なく、リレー用鉄心、ヨークなどの電気・電子部品の素材用の鉄源や、真空誘導溶解炉などでの特殊な合金鋼製造用の鉄源として広く使用されている。 Pure iron (also referred to as “industrial pure iron”) has a low content of impurities such as carbon, silicon, and manganese, and is an iron source for materials for electrical and electronic parts such as relay cores and yokes, and vacuum induction melting. Widely used as an iron source for producing special alloy steel in furnaces.
種々の純鉄のなかで、銑鋼一貫製鉄所において、転炉での精錬とＲＨ真空脱ガス装置での精錬とを組み合わせて溶製される純鉄（「転炉鋼純鉄」とも記す）は、大量生産が可能であり、他の製造方法によって製造される純鉄に比較して安価であり、主に、電解鉄の代替として、電気炉や真空誘導溶解炉で大量に使用されている。転炉鋼純鉄の化学成分については、主に、炭素（Ｃ）、燐（Ｐ）、硫黄（Ｓ）の含有量が少ないことが求められている。尚、電解鉄とは、鉄塩水溶液の電解によって得られる純鉄で、通常、含有される不純物元素は、炭素０．００５質量％以下、珪素０．００５質量％以下、マンガン０．００５質量％以下、燐０．００４質量％以下、硫黄０．００５質量％以下である（ＪＩＳ工業用語大辞典、第５版、２００１年３月３０日発行を参照）。 Among various types of pure iron, pure iron that is melted by combining refining in the converter and refining in the RH vacuum degassing unit at the integrated steelworks of the steel industry (also referred to as “converter steel pure iron”) Can be mass-produced and is cheaper than pure iron produced by other production methods, and is mainly used in large quantities in electric furnaces and vacuum induction melting furnaces as an alternative to electrolytic iron . The chemical components of converter steel pure iron are mainly required to have a low content of carbon (C), phosphorus (P), and sulfur (S). In addition, electrolytic iron is pure iron obtained by electrolysis of an iron salt aqueous solution, and usually contained impurity elements are carbon 0.005 mass% or less, silicon 0.005 mass% or less, manganese 0.005 mass%. Hereinafter, phosphorus is 0.004% by mass or less and sulfur is 0.005% by mass or less (see JIS Industrial Glossary, 5th edition, issued on March 30, 2001).
航空機材には疲労特性が求められており、鋼中の窒素含有量が高いと窒化アルミニウム（ＡｌＮ）などの窒化物が結晶粒界に形成しやすく、疲労破壊の起点となりやすい。また、純鉄を再溶解する真空誘導溶解炉などでは脱窒反応に限界があり、そのため、航空機材用途の鉄源としての純鉄には、窒素含有量が少ないことが要求されている。同様に、転炉鋼純鉄においても窒素含有量の少ないこと、具体的には、窒素含有量が０．００１６質量％以下であることが要求されている。 Aircraft materials are required to have fatigue characteristics, and when the nitrogen content in steel is high, nitrides such as aluminum nitride (AlN) are likely to form at the grain boundaries, which tends to be the starting point of fatigue failure. Moreover, in a vacuum induction melting furnace or the like for remelting pure iron, there is a limit to the denitrification reaction. Therefore, pure iron as an iron source for aircraft materials is required to have a low nitrogen content. Similarly, the converter steel pure iron is also required to have a low nitrogen content, specifically, a nitrogen content of 0.0016% by mass or less.
溶鋼の二次精錬工程において、ＲＨ真空脱ガス装置による高真空処理が普及して以降、窒素含有量が０．００８０質量％以下の低窒素鋼は容易に溶製可能となった。しかし、窒素含有量の更なる低い極低窒素鋼を溶製するべく、従来、種々の提案がなされている。 In the secondary refining process of molten steel, low nitrogen steel having a nitrogen content of 0.0080% by mass or less can be easily melted since high vacuum processing using an RH vacuum degassing apparatus has become widespread. However, various proposals have heretofore been made in order to melt ultra-low nitrogen steel having a still lower nitrogen content.
例えば、特許文献１には、ＲＨ真空脱ガス装置での処理中に、上昇側浸漬管及び下降側浸漬管の少なくとも耐火物が溶湯に浸漬されない大気への露出部分を遮蔽囲いで包囲し、該遮蔽囲い内に水素もしくは水素と不活性ガスとの混合ガスを供給して前記耐火物の露出部分をガスで覆い、大気との接触を遮断してガスシールするようにした、ＲＨ真空脱ガス装置における吸窒防止方法が提案されている。この方法によれば吸窒防止は可能であるが、脱ガス処理前の溶鋼の窒素含有量が０．００１６質量％を超える場合には、鋼中の窒素含有量を０．００１６質量％以下に調整することは容易でない。 For example, in Patent Document 1, during the processing in the RH vacuum degassing apparatus, at least the refractory material of the ascending-side dip tube and the descending-side dip tube is surrounded by a shielding enclosure that is not immersed in the molten metal, An RH vacuum degassing device in which hydrogen or a mixed gas of hydrogen and an inert gas is supplied into a shielding enclosure to cover the exposed portion of the refractory with gas, and gas sealing is performed by blocking contact with the atmosphere. Nitrogen absorption prevention methods have been proposed. According to this method, it is possible to prevent nitrogen absorption, but when the nitrogen content of the molten steel before degassing treatment exceeds 0.0016% by mass, the nitrogen content in the steel is set to 0.0016% by mass or less. It is not easy to adjust.
特許文献２には、ランタン（Ｌａ）、セリウム（Ｃｅ）及びネオジム（Ｎｄ）のうちの一種または二種以上の希土類金属を、ＲＨ真空脱ガス装置にて処理中の溶鋼に添加して脱窒を促進させ、窒素含有量が０．００２５質量％以下の溶鋼を溶製する方法が提案されている。この方法によれば、脱窒剤として機能する希土類金属の添加により、脱窒を効果的に促進できるものの、溶鋼中に希土類金属の酸化物が残留し、連続鋳造工程において、取鍋のノズルまたはタンディッシュの浸漬ノズルの内壁に前記酸化物が付着・成長し、ノズル詰りのトラブル発生を助長させる。 Patent Document 2 describes denitrification by adding one or more rare earth metals of lanthanum (La), cerium (Ce), and neodymium (Nd) to molten steel being processed by an RH vacuum degassing apparatus. Has been proposed, and a method for melting molten steel having a nitrogen content of 0.0025% by mass or less has been proposed. According to this method, although the denitrification can be effectively promoted by the addition of the rare earth metal functioning as a denitrification agent, the rare earth metal oxide remains in the molten steel, and in the continuous casting process, the ladle nozzle or The oxide adheres to and grows on the inner wall of the submerged nozzle of the tundish, which promotes the occurrence of nozzle clogging troubles.
特許文献３には、ＲＨ真空脱ガス装置の真空槽内の溶鋼に粒径１０〜２００μｍの酸化剤粉体を吹きつけて脱窒することが提案されている。しかしながら、本発明の対象とする純鉄の溶製においては酸化剤中の微量の不純物元素によって要求成分を満足できない場合が発生する可能性があり、使用する酸化剤の管理を厳格化する必要がある。また、ＲＨ真空脱ガス装置では酸化剤を吹き込むための設備が必要となる。 Patent Document 3 proposes denitrification by spraying an oxidant powder having a particle size of 10 to 200 μm on molten steel in a vacuum tank of an RH vacuum degassing apparatus. However, in the melting of pure iron that is the subject of the present invention, there may be a case where the required components cannot be satisfied due to a trace amount of impurity elements in the oxidant, and it is necessary to strictly control the oxidant to be used. is there. Further, the RH vacuum degassing apparatus requires equipment for blowing in the oxidant.
特許文献４には、取鍋内溶鋼に直胴型浸漬管を浸漬し該管内を減圧するとともに、取鍋の底部からガスを供給して鋼浴を攪拌する真空精錬装置において、前記管内の真空度、攪拌ガス流量などを所定の範囲に制御し、脱窒を促進させる方法が提案されている。この方法では、取鍋底から吹き込んだガスにより、直胴型浸漬管外の溶鋼とスラグとが攪拌され、スラグ−メタル反応が助長されて、スラグからの復燐が懸念される。 Patent Document 4 discloses a vacuum refining apparatus in which a straight barrel type dip tube is immersed in molten steel in a ladle to decompress the inside of the tube and gas is supplied from the bottom of the ladle to stir the steel bath. A method for promoting the denitrification by controlling the flow rate and the stirring gas flow rate within a predetermined range has been proposed. In this method, the molten steel and the slag outside the straight barrel type dip tube are agitated by the gas blown from the bottom of the ladle, the slag-metal reaction is promoted, and there is a concern about the recovery from the slag.
特許文献５には、転炉出鋼時の鋼中炭素含有量を０．１０質量％以上とし、ＲＨ真空脱ガス装置での処理中に酸素含有ガスを溶鋼に吹き付けて脱炭し、この脱炭反応によって発生するＣＯガスにより脱窒を促進させ、鋼中窒素含有量を０．００２０質量％以下にする方法が提案されている。しかし、この方法では、出鋼時の溶鋼炭素含有量を０．１０質量％以上にする必要があるので、転炉での脱燐反応が進行しにくく、純鉄で要求される燐含有量の少ない溶鋼を得ることができない。 In Patent Document 5, the carbon content in the steel at the time of conversion from the converter is set to 0.10% by mass or more, and decarburization is performed by blowing an oxygen-containing gas onto the molten steel during the treatment in the RH vacuum degassing apparatus. A method has been proposed in which denitrification is promoted by CO gas generated by a charcoal reaction so that the nitrogen content in steel is 0.0020% by mass or less. However, in this method, since the molten steel carbon content at the time of steel output needs to be 0.10% by mass or more, the dephosphorization reaction in the converter is difficult to proceed, and the phosphorus content required for pure iron is reduced. Less molten steel cannot be obtained.
特許文献６には、転炉によって溶鋼中炭素濃度を製品の最終目標値よりも０．１５〜０．８質量％低く脱炭精錬した後、出鋼するにあたり、転炉吹錬終了後、出鋼までの間には、強制脱酸剤を使用することなく出鋼するとともに、出鋼期間の前半においては、強制脱酸剤を使用することなく、取鍋中に加炭剤を添加して加炭剤と取鍋中に出鋼される溶鋼との反応によって生ずるＣＯガスによって溶鋼流及び取鍋内溶鋼を大気から遮断して窒素のピックアップを阻止し、出鋼期間の後半においては、珪素及びマンガンによる脱酸を行って、高炭素低窒素鋼を溶製する方法が提案されている。 In Patent Document 6, after decarburizing and refining the carbon concentration in the molten steel by 0.15 to 0.8 mass% lower than the final target value of the product by a converter, In the first half of the steelmaking period, a carburizing agent is added to the ladle without using a forced deoxidizing agent. The CO gas generated by the reaction between the carburizing agent and the molten steel discharged in the ladle blocks the molten steel flow and the molten steel in the ladle from the atmosphere to prevent nitrogen pick-up. In addition, a method of melting high-carbon low-nitrogen steel by deoxidation with manganese has been proposed.
この方法では、出鋼時の窒素のピックアップを阻止することはできるが、この方法だけでは、溶鋼中窒素濃度を０．００３０質量％以下にすることはできず、溶鋼に脱窒剤として機能するチタン（Ｔｉ）を添加して溶鋼中の窒素を強制的に除去するなどの対策が別途必要である。また、特許文献６は、高炭素鋼の溶製を対象とする技術であり、また、ＲＨ真空脱ガス装置を使用しておらず、特許文献６の技術をそのまま純鉄の溶製方法に適用することはできない。 With this method, it is possible to prevent the pickup of nitrogen at the time of steel production, but with this method alone, the nitrogen concentration in the molten steel cannot be reduced to 0.0030% by mass or less, and it functions as a denitrifying agent in the molten steel. Additional measures such as forcibly removing nitrogen in the molten steel by adding titanium (Ti) are necessary. Patent Document 6 is a technique for melting high carbon steel, and does not use an RH vacuum degassing apparatus, and the technique of Patent Document 6 is directly applied to a pure iron melting method. I can't do it.
上記のように、極低窒素鋼を溶製する技術は幾つか提案されているが、本発明の対象である純鉄は燐含有量が０．００２５質量％以下と少ないことも必須条件であり、上記の従来技術では、純鉄に要求される極低窒素（窒素含有量≦０．００１６質量％）及び極低燐（燐含有量≦０．００２５質量％）を同時に達成することはできない。 As described above, several techniques for melting ultra-low nitrogen steel have been proposed, but it is also an essential condition that the pure iron which is the object of the present invention has a low phosphorus content of 0.0025% by mass or less. In the above-described prior art, the extremely low nitrogen (nitrogen content ≦ 0.0016 mass%) and the extremely low phosphorus (phosphorus content ≦ 0.0025 mass%) required for pure iron cannot be achieved at the same time.
本発明はこのような事情に鑑みてなされたもので、その目的とするところは、特段の設備改造を行うことなく、高炉から出銑された溶銑の転炉での精錬と、転炉精錬で得られた溶鋼のＲＨ真空脱ガス装置での精錬とを組み合わせて、窒素含有量の少ない純鉄を安価で安定的に溶製することのできる、極低窒素純鉄の溶製方法を提供することである。 The present invention has been made in view of such circumstances, and the object of the present invention is to refining the hot metal discharged from the blast furnace in the converter and the refining of the converter without any special equipment modification. Provided is an ultra-low nitrogen pure iron melting method capable of stably and inexpensively melting pure iron with a low nitrogen content by combining refining of the obtained molten steel with an RH vacuum degassing apparatus. That is.
本発明者らは、上記課題を解決するべく、転炉での脱炭精錬条件及びＲＨ真空脱ガス装置での精錬条件を詳細に検討した。特に、溶鋼中の窒素含有量を低下させるための処理条件と、純鉄の仕様条件である極低燐の規格と、を同時に満足させる処理方法を確立することによって、上記課題が解決できることを見出した。 In order to solve the above problems, the present inventors have studied in detail the decarburization refining conditions in the converter and the refining conditions in the RH vacuum degassing apparatus. In particular, it has been found that the above problem can be solved by establishing a treatment method that simultaneously satisfies the treatment conditions for reducing the nitrogen content in the molten steel and the specifications for ultra-low phosphorus, which is a specification condition for pure iron. It was.
本発明は上記知見に基づきなされたものであり、その要旨は以下のとおりである。
［１］溶銑を転炉で脱炭精錬して、該脱炭精錬によって得られる溶鋼の燐含有量を０．００２５質量％以下とし、次いで、転炉での脱炭精錬終了から出鋼までの期間及び出鋼中に前記溶鋼に強制脱酸剤を加えることなく、前記溶鋼を転炉から取鍋に出鋼し、出鋼前に予め取鍋内に入れ置きした炭素源または出鋼時に取鍋内に添加した炭素源と、出鋼される溶鋼とを反応させ、炭素源と溶鋼との反応によって溶鋼の炭素含有量を上昇させるとともに、炭素源と溶鋼との反応によって生ずるＣＯガスによって取鍋内溶鋼を大気から遮断して溶鋼の窒素ピックアップを抑制し、その後、取鍋内の溶鋼に、溶鋼の炭素含有量が０．００５０質量％以下となるまで、ＲＨ真空脱ガス装置での減圧下の脱炭精錬を施すことを特徴とする、極低窒素純鉄の溶製方法。
［２］前記極低窒素純鉄は、窒素含有量が０．００１６質量％以下、且つ、燐含有量が０．００２５質量％以下であることを特徴とする、上記［１］に記載の極低窒素純鉄の溶製方法。
［３］前記炭素源と前記溶鋼とを反応させた後の取鍋内の溶鋼の炭素含有量を０．０５〜０．０９質量％に調整することを特徴とする、上記［１］または上記［２］に記載の極低窒素純鉄の溶製方法。
The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] The hot metal is decarburized and refined in a converter, and the phosphorus content of the molten steel obtained by the decarburization and refinement is 0.0025% by mass or less. Next, from the end of decarburization and refining in the converter to the output steel Without adding a forced deoxidizer to the molten steel during the period and during the steel extraction, the molten steel is extracted from the converter to the ladle and taken in advance at the time of the carbon source or the steel extracted before placing in the ladle. The carbon source added to the pan reacts with the molten steel to be discharged, the carbon content of the molten steel is increased by the reaction between the carbon source and the molten steel, and the carbon gas generated by the reaction between the carbon source and the molten steel is taken up. The molten steel in the ladle is cut off from the atmosphere to suppress nitrogen pick-up of the molten steel, and then the reduced pressure in the RH vacuum degasser until the molten steel in the ladle has a carbon content of 0.0050% by mass or less. A solution of ultra-low nitrogen pure iron Method.
[2] The pole according to [1], wherein the ultra-low nitrogen pure iron has a nitrogen content of 0.0016% by mass or less and a phosphorus content of 0.0025% by mass or less. Low nitrogen pure iron melting method.
[3] The above [1] or the above, wherein the carbon content of the molten steel in the ladle after reacting the carbon source and the molten steel is adjusted to 0.05 to 0.09% by mass. The method for melting ultra-low nitrogen pure iron according to [2].
本発明によれば、出鋼時に、炭素源と出鋼される溶鋼とを反応させ、この反応によって溶鋼の炭素含有量を上昇させるとともに、この反応によって生ずるＣＯガスによって取鍋内溶鋼を大気から遮断して溶鋼の窒素ピックアップを抑制し、その後、取鍋内の溶鋼に、溶鋼の炭素含有量が０．００５０質量％以下となるまで、ＲＨ真空脱ガス装置での減圧下の脱炭精錬を施して溶鋼中窒素の除去を促進させるので、特段の設備改造を行うことなく、転炉での精錬とＲＨ真空脱ガス装置での精錬との組み合わせにより、窒素含有量の少ない極低窒素純鉄を安定して溶製することが実現される。 According to the present invention, at the time of steel production, the carbon source and the molten steel to be produced are reacted, the carbon content of the molten steel is increased by this reaction, and the molten steel in the ladle is removed from the atmosphere by the CO gas generated by this reaction. Cut off and suppress nitrogen pick-up of the molten steel, and then decarburize and refining the molten steel in the ladle under reduced pressure with an RH vacuum degasser until the carbon content of the molten steel is 0.0050 mass% or less. Because it promotes the removal of nitrogen in molten steel, the combination of refining in the converter and refining in the RH vacuum degassing unit does not require any special equipment modification. Can be stably melted.
以下、本発明を具体的に説明する。 Hereinafter, the present invention will be specifically described.
図１に、本発明における極低窒素純鉄の溶製プロセスを示す。本発明では、図１に示すように、高炉で溶製された溶銑を鉄源とし、この溶銑に脱燐処理及び脱硫処理の予備処理を施し、予備処理された溶銑を転炉で脱炭精錬する。この脱炭精錬で得られた溶鋼を、転炉から取鍋への出鋼時に炭素源によって脱酸・加炭し、この脱酸・加炭された溶鋼にＲＨ真空脱ガス装置での減圧下の脱炭精錬（「真空脱炭」という）を施し、窒素含有量が０．００１６質量％以下、燐含有量が０．００２５質量％以下の極低窒素純鉄を溶製する。溶製された溶鋼は、連続鋳造機などの鋳造工程を経てビレット、ブルーム、スラブなどの鋼片となる。 FIG. 1 shows a melting process of ultra-low nitrogen pure iron in the present invention. In the present invention, as shown in FIG. 1, hot metal melted in a blast furnace is used as an iron source, the hot metal is subjected to dephosphorization and desulfurization pretreatment, and the pretreated hot metal is decarburized and refined in a converter. To do. The molten steel obtained by this decarburization refining is deoxidized and carburized by a carbon source when steel is discharged from the converter to the ladle, and the deoxidized and carburized molten steel is subjected to reduced pressure in an RH vacuum degassing device. The decarburization refining (referred to as “vacuum decarburization”) is performed to melt ultra-low nitrogen pure iron having a nitrogen content of 0.0016 mass% or less and a phosphorus content of 0.0025 mass% or less. The molten steel is made into billets, blooms, slabs and other steel pieces through a casting process such as a continuous casting machine.
本発明の溶製対象である極低窒素純鉄の化学成分は、上記のように、窒素含有量が０．００１６質量％以下、燐含有量が０．００２５質量％以下である以外に、炭素含有量が０．００５質量％以下、珪素含有量が０．００５質量％以下、マンガン含有量が０．０７質量％以下、硫黄含有量が０．００５質量％以下、アルミニウム含有量が０．００５質量％以下である。 As described above, the chemical component of the ultra-low nitrogen pure iron that is the melting target of the present invention is carbon, in addition to the nitrogen content of 0.0016% by mass or less and the phosphorus content of 0.0025% by mass or less. The content is 0.005% by mass or less, the silicon content is 0.005% by mass or less, the manganese content is 0.07% by mass or less, the sulfur content is 0.005% by mass or less, and the aluminum content is 0.005. It is below mass%.
以下、各工程順に説明する。 Hereinafter, it demonstrates in order of each process.
高炉で溶製され、高炉から出銑された溶銑を混銑車や溶銑鍋で受銑する。受銑した溶銑に、予備処理として脱燐処理及び脱硫処理を施し、溶銑の燐含有量及び硫黄含有量を低下させる。極低窒素純鉄では、不純物成分の含有量が少ないことが望まれている。従って、脱燐処理では溶銑の燐濃度が０．０４０質量％以下、望ましくは０．０３０質量％以下となるまで脱燐処理することが好ましく、脱硫処理では溶銑の硫黄濃度が０．００５０質量％以下、望ましくは０．００３０質量％以下となるまで脱硫処理することが好ましい。脱燐処理することで、自ずと、溶銑の珪素濃度は０．０１質量％以下に低下する。 The molten iron produced in the blast furnace and received from the blast furnace is received in a kneading car or hot metal ladle. The received hot metal is subjected to dephosphorization treatment and desulfurization treatment as a preliminary treatment to reduce the phosphorus content and sulfur content of the hot metal. In extremely low nitrogen pure iron, it is desired that the content of impurity components is small. Accordingly, in the dephosphorization treatment, it is preferable to perform the dephosphorization treatment until the phosphorus concentration in the hot metal is 0.040 mass% or less, desirably 0.030 mass% or less, and in the desulfurization treatment, the sulfur concentration in the hot metal is 0.0050 mass%. In the following, it is preferable to perform the desulfurization treatment until it becomes 0.0030% by mass or less. By carrying out the dephosphorization treatment, the silicon concentration of the hot metal is naturally reduced to 0.01% by mass or less.
脱燐処理は、例えば、酸素ガスなどの酸素源と生石灰とを溶銑に供給し、溶銑中の燐を酸素源で酸化させ、生成する燐酸化物を滓化した生石灰で取り込む方法を用いることができる。脱硫処理は、生石灰などの脱硫剤と溶銑とを機械的に攪拌し、溶銑中の硫黄を脱硫剤に吸収する方法を用いることができる。脱燐処理及び脱硫処理の順序はどちらが先であっても構わない。 In the dephosphorization treatment, for example, a method of supplying an oxygen source such as oxygen gas and quick lime to hot metal, oxidizing phosphorus in the hot metal with the oxygen source, and taking in the generated quick oxide with the converted quick lime can be used. . In the desulfurization treatment, a method of mechanically stirring a desulfurizing agent such as quick lime and hot metal and absorbing sulfur in the hot metal into the desulfurizing agent can be used. Whichever order the dephosphorization treatment and the desulfurization treatment may be performed first.
脱燐処理及び脱硫処理の施された溶銑を転炉に装入し、上吹きランスまたは底吹き羽口から酸素ガスを供給し、溶銑に脱炭精錬を施し、溶銑から溶鋼を溶製する。この脱炭精錬によって溶鋼中珪素濃度は０．００５質量％以下に低減する。 The hot metal that has been subjected to dephosphorization and desulfurization treatment is charged into a converter, oxygen gas is supplied from an upper blowing lance or bottom blowing tuyere, decarburization refining is performed on the hot metal, and molten steel is produced from the hot metal. By this decarburization refining, the silicon concentration in the molten steel is reduced to 0.005 mass% or less.
本発明においては、脱炭精錬によって得られる溶鋼は、その燐含有量が極低窒素純鉄の規格（燐濃度≦０．００２５質量％）を満足することが必要である。従って、転炉での脱炭精錬では、炉内に生成するスラグの塩基度（(質量％ＣａＯ)／(質量％ＳｉＯ2)）を２．５以上に制御し、脱燐反応を促進させる。本発明者らは、脱炭精錬に供する溶銑の燐含有量が０．０４０質量％以下であれば、上記の転炉脱炭精錬によって得られる溶鋼の燐含有量は０．００２５質量％以下となることを確認している。 In the present invention, the molten steel obtained by decarburization refining must have a phosphorus content satisfying the standard of extremely low nitrogen pure iron (phosphorus concentration ≦ 0.0025 mass%). Therefore, in the decarburization refining in the converter, the basicity ((mass% CaO) / (mass% SiO 2 )) of the slag generated in the furnace is controlled to 2.5 or more to promote the dephosphorization reaction. If the phosphorus content of the hot metal to be subjected to decarburization refining is 0.040 mass% or less, the phosphorus content of the molten steel obtained by the converter decarburization refining is 0.0025 mass% or less. Confirm that it will be.
但し、上記脱炭精錬によって脱炭精錬終了時の溶鋼の燐含有量を０．００２５質量％以下とするためには、脱燐反応を促進させることが必要であり、そのために、本発明では、脱炭精錬終了時の溶鋼の炭素濃度を０．０４０質量％以下、好ましくは０．０２０質量％以下に吹き下げる。これは、炭素及び燐の酸素との親和力は同等であり、溶鋼中炭素濃度が低下するほど、脱燐反応が促進されるからである。 However, in order to make the phosphorus content of the molten steel at the end of the decarburization refining 0.0025% by mass or less by the decarburization refining, it is necessary to promote the dephosphorization reaction. The carbon concentration of the molten steel at the end of decarburization refining is blown down to 0.040 mass% or less, preferably 0.020 mass% or less. This is because carbon and phosphorus have the same affinity for oxygen, and the dephosphorization reaction is promoted as the carbon concentration in the molten steel decreases.
図２は、極低窒素純鉄溶製時での転炉脱炭精錬終了時点での溶鋼中燐濃度と溶鋼中炭素濃度との関係の調査結果を示す図である。図２に示すように、脱炭精錬終了時の溶鋼中燐濃度を０．００２５質量％以下とするためには、脱炭精錬終了時の溶鋼中炭素濃度を少なくとも０．０４０質量％以下にする必要があり、安定して溶鋼中燐濃度を０．００２５質量％以下とするためには、脱炭精錬終了時の溶鋼中炭素濃度を０．０２０質量％程度に制御することが必要となる。 FIG. 2 is a diagram showing the results of an investigation of the relationship between the phosphorus concentration in molten steel and the carbon concentration in molten steel at the end of converter decarburization refining when melting ultra-low nitrogen pure iron. As shown in FIG. 2, in order to set the phosphorus concentration in the molten steel at the end of decarburization refining to 0.0025 mass% or less, the carbon concentration in the molten steel at the end of decarburization refining is set to at least 0.040 mass% or less. Therefore, in order to stably set the phosphorus concentration in the molten steel to 0.0025 mass% or less, it is necessary to control the carbon concentration in the molten steel at the end of decarburization refining to about 0.020 mass%.
本発明では、極低窒素純鉄の窒素含有量を０．００１６質量％以下とするために、転炉から取鍋への出鋼中の大気から溶鋼への窒素のピックアップを抑制する対策を実施し、且つ、ＲＨ真空脱ガス装置では、真空脱炭での脱炭量を確保することによって、窒素の溶鋼からの分離除去を促進させる対策を実施する。 In the present invention, in order to make the nitrogen content of ultra-low nitrogen pure iron 0.0016% by mass or less, measures are taken to suppress the pickup of nitrogen from the atmosphere into the molten steel in the steel output from the converter to the ladle. In addition, in the RH vacuum degassing apparatus, measures are taken to promote separation and removal of nitrogen from molten steel by securing a decarburization amount in vacuum decarburization.
しかしながら、上記のように、転炉での脱炭精錬終了時の溶鋼中燐濃度を０．００２５質量％以下とするために、転炉脱炭精錬終了時の溶鋼中炭素濃度を０．０４０質量％以下へと低下させている。一方、溶鋼中炭素濃度を０．０４０質量％以下とすることで、脱炭精錬終了時の溶鋼の溶存酸素濃度は０．０６質量％以上に高くなっている。 However, as described above, in order to set the phosphorus concentration in the molten steel at the end of decarburization refining in the converter to 0.0025% by mass or less, the carbon concentration in the molten steel at the end of converter decarburization refining is 0.040 mass. % Or less. On the other hand, by setting the carbon concentration in the molten steel to 0.040 mass% or less, the dissolved oxygen concentration of the molten steel at the end of decarburization refining is increased to 0.06 mass% or more.
そこで、本発明では、取鍋内に予め炭素源を入れ置きする、または、出鋼時に取鍋内に炭素源を添加し、この炭素源と出鋼される溶鋼とを反応させ、溶鋼の脱酸処理及び加炭処理を実施する。炭素源と溶鋼中の溶存酸素とが反応（脱酸反応）してＣＯガスが発生し、発生するＣＯガスによって取鍋内の溶鋼は大気から遮断され、大気から溶鋼への窒素のピックアップが抑制される。また、炭素源は溶鋼中に溶解し、溶鋼中の炭素濃度が上昇する（加炭処理）。炭素源としては、コークス、土壌黒鉛、カーボンブラックなどが使用可能であるが、硫黄などの不純物含有量の少ない土壌黒鉛やカーボンブラックが好適である。 Therefore, in the present invention, a carbon source is placed in the ladle in advance, or a carbon source is added to the ladle at the time of steel extraction, and the carbon source reacts with the molten steel to be discharged to remove the molten steel. Perform acid treatment and carburizing treatment. The carbon source and dissolved oxygen in the molten steel react (deoxidation reaction) to generate CO gas. The generated CO gas blocks the molten steel in the ladle from the atmosphere and suppresses the pickup of nitrogen from the atmosphere to the molten steel. Is done. Moreover, a carbon source melt | dissolves in molten steel, and the carbon concentration in molten steel rises (carburizing process). As the carbon source, coke, soil graphite, carbon black and the like can be used, but soil graphite and carbon black having a low content of impurities such as sulfur are preferable.
アルミニウム、珪素、マンガン、チタンなどの強制脱酸剤を溶鋼に添加することでも溶鋼は脱酸されるが、これらの強制脱酸剤を使用した場合にはＣＯガスが生成せず、溶鋼を大気から遮断する効果は得られない。また、極低窒素純鉄では、アルミニウム、珪素、マンガン、チタンなどの成分も低いことが望まれている。従って、本発明では、転炉での脱炭精錬終了から出鋼までの期間及び出鋼中に、強制脱酸剤を溶鋼に添加することは行わない。 Addition of forced deoxidizers such as aluminum, silicon, manganese, and titanium to molten steel also deoxidizes molten steel. However, when these forced deoxidizers are used, CO gas is not generated and the molten steel is removed from the atmosphere. The effect of blocking from is not obtained. In addition, in ultra-low nitrogen pure iron, it is desired that components such as aluminum, silicon, manganese, and titanium are also low. Therefore, in the present invention, the forced deoxidizer is not added to the molten steel during the period from the end of decarburization refining in the converter to the output steel and during the output steel.
このように調整した取鍋内の溶鋼に、ＲＨ真空脱ガス装置において真空脱炭精錬を施す。溶存酸素を含有する溶鋼を真空槽内において減圧下に曝すことで、溶鋼中の溶存酸素と炭素とが反応して脱炭反応（Ｃ＋Ｏ→ＣＯ）が進行する。溶鋼を減圧下に曝すことで、溶鋼中の窒素は除去されるが、発生するＣＯガスによって溶鋼中からの窒素の除去（脱窒）がより一層進行する。尚、ＲＨ真空脱ガス装置では、大気からの吸窒が少なからず処理中の溶鋼に発生するので、真空脱炭精錬中に溶鋼の窒素濃度が上昇することもあるが、真空脱炭精錬での脱炭量を増加させることで吸窒を抑制することができる。 The molten steel in the ladle thus adjusted is subjected to vacuum decarburization refining in an RH vacuum degassing apparatus. By exposing the molten steel containing dissolved oxygen under reduced pressure in the vacuum chamber, the dissolved oxygen in the molten steel reacts with carbon, and the decarburization reaction (C + O → CO) proceeds. Nitrogen in the molten steel is removed by exposing the molten steel under reduced pressure, but removal (denitrification) of nitrogen from the molten steel further proceeds by the generated CO gas. In the RH vacuum degassing device, nitrogen absorption from the atmosphere occurs in the molten steel being processed, so the nitrogen concentration of the molten steel may increase during the vacuum decarburization refining. Nitrogen absorption can be suppressed by increasing the amount of decarburization.
溶鋼中の溶存酸素が減少すると脱炭反応が停滞する。このような場合には、真空槽内に設置した上吹きランスから酸素ガスを、真空槽内を環流する溶鋼に吹き付けて脱炭反応を促進させる。脱炭反応が進行して溶鋼の炭素濃度が０．００５０質量％以下の任意の値になったなら、脱ガス精錬を終了する。尚、真空脱炭精錬の終了後、溶鋼中溶存酸素が過剰に高くなった場合には、溶存酸素の当量以下の強制脱酸剤を添加し、溶鋼を脱酸しても構わない。 When the dissolved oxygen in molten steel decreases, the decarburization reaction stagnates. In such a case, the decarburization reaction is promoted by blowing oxygen gas from the upper blowing lance installed in the vacuum chamber to the molten steel circulating in the vacuum chamber. When the decarburization reaction proceeds and the carbon concentration of the molten steel reaches an arbitrary value of 0.0050 mass% or less, the degassing refining is terminated. If the dissolved oxygen in the molten steel becomes excessively high after the vacuum decarburization refining, the molten steel may be deoxidized by adding a forced deoxidizer equal to or less than the equivalent of dissolved oxygen.
図３は、極低窒素純鉄溶製時での出鋼後の取鍋内溶鋼の炭素濃度と出鋼後の取鍋内溶鋼の窒素濃度との関係の調査結果を示す図である。図３からも明らかなように、取鍋内溶鋼の炭素濃度が高いほど、溶鋼中の窒素濃度は低いことがわかる。つまり、出鋼前の溶鋼の炭素濃度は０．０４０質量％以下であることから、炭素源による加炭量が多いほど、窒素のピックアップが抑制されることがわかった。 FIG. 3 is a diagram showing the results of an investigation of the relationship between the carbon concentration of the molten steel in the ladle after steelmaking and the nitrogen concentration of the molten steel in the ladle after steelmaking when producing ultra-low nitrogen pure iron. As is clear from FIG. 3, it can be seen that the higher the carbon concentration of the molten steel in the ladle, the lower the nitrogen concentration in the molten steel. That is, since the carbon concentration of the molten steel before steel is 0.040% by mass or less, it was found that the more the amount of carburizing by the carbon source, the more the nitrogen pickup is suppressed.
図４は、極低窒素純鉄溶製時でのＲＨ真空脱ガス装置での真空脱炭精錬時の脱炭量と脱ガス処理後の溶鋼中窒素濃度との関係の調査結果を示す図である。図４に示すように、真空脱炭精錬時の脱炭量が多くなるほど、脱ガス処理後の溶鋼中窒素濃度は低下する傾向であることがわかった。 FIG. 4 is a diagram showing the results of an investigation of the relationship between the amount of decarburization during vacuum decarburization and refining and the nitrogen concentration in the molten steel after degassing with an RH vacuum degassing unit when producing ultra-low nitrogen pure iron. is there. As shown in FIG. 4, it was found that the nitrogen concentration in the molten steel after degassing tends to decrease as the amount of decarburization during vacuum decarburization refining increases.
つまり、図３及び図４の結果から、加炭処理後の溶鋼中炭素濃度を０．０５〜０．０９質量％に上昇させ、且つ、この炭素分をＲＨ真空脱ガス装置での真空脱炭精錬で除去することで、極低窒素純鉄の窒素含有量を安定して０．００１６質量％以下に制御できることがわかった。加炭処理後の溶鋼中炭素濃度を、０．０９質量％を超える範囲まで上昇させると、次工程の真空脱炭精錬が長くなるので好ましくない。但し、図４に示すように、真空脱炭時の脱炭量が０．０５質量％未満であっても極低窒素純鉄の窒素含有量を０．００１６質量％以下に制御できるので、加炭処理後の溶鋼中炭素濃度を０．０５〜０．０９質量％の範囲に上昇させることは、本発明において必須の条件ではない。 That is, from the results of FIGS. 3 and 4, the carbon concentration in the molten steel after the carburizing treatment is increased to 0.05 to 0.09 mass%, and this carbon content is vacuum decarburized by the RH vacuum degassing apparatus. It was found that the nitrogen content of ultra-low nitrogen pure iron can be stably controlled to 0.0016% by mass or less by removing by refining. Increasing the carbon concentration in the molten steel after the carburizing treatment to a range exceeding 0.09 mass% is not preferable because the vacuum decarburization refining in the next step becomes longer. However, as shown in FIG. 4, even if the decarburization amount during vacuum decarburization is less than 0.05% by mass, the nitrogen content of extremely low nitrogen pure iron can be controlled to 0.0016% by mass or less. Increasing the carbon concentration in the molten steel after charcoal treatment to a range of 0.05 to 0.09 mass% is not an essential condition in the present invention.
以上説明したように、本発明によれば、出鋼時に、炭素源と出鋼される溶鋼とを反応させ、この反応によって溶鋼の炭素含有量を上昇させるとともに、この反応によって生ずるＣＯガスによって取鍋内溶鋼を大気から遮断して溶鋼の窒素ピックアップを抑制し、その後、取鍋内の溶鋼に、溶鋼の炭素含有量が０．００５０質量％以下となるまで、ＲＨ真空脱ガス装置での減圧下の脱炭精錬を施して溶鋼中窒素の除去を促進させるので、特段の設備改造を行うことなく、転炉での精錬とＲＨ真空脱ガス装置での精錬との組み合わせにより、窒素含有量の少ない極低窒素純鉄を安定して溶製することが実現される。 As described above, according to the present invention, at the time of steel output, the carbon source and the molten steel to be output are reacted, and the carbon content of the molten steel is increased by this reaction. The molten steel in the ladle is cut off from the atmosphere to suppress nitrogen pick-up of the molten steel, and then the reduced pressure in the RH vacuum degasser until the molten steel in the ladle has a carbon content of 0.0050% by mass or less. Since the removal of nitrogen in molten steel is promoted by the following decarburization refining, the nitrogen content can be reduced by combining refining in the converter and refining in the RH vacuum degassing unit without special equipment modification. It is possible to stably melt a small amount of ultra-low nitrogen pure iron.
以下、実施例によって本発明を更に具体的に説明する。 Hereinafter, the present invention will be described more specifically with reference to examples.
図１に示す溶製プロセスに沿って本発明を適用し、極低窒素純鉄を溶製する試験を実施した（本発明例）。出鋼時の脱酸・加炭用の炭素源としてはカーボンブラックを使用し、カーボンブラックを取鍋内に予め入れ置きした。また、比較のために、出鋼時に脱酸・加炭用の炭素源を使用せずに、その他の条件は本発明例に沿って極低窒素純鉄を溶製する試験も実施した（比較例）。本発明例及び比較例は、どちらも出鋼時の溶鋼中炭素含有量は０．０４質量％以下であった。 The present invention was applied along the melting process shown in FIG. 1, and a test for melting ultra-low nitrogen pure iron was carried out (example of the present invention). Carbon black was used as a carbon source for deoxidation and carburizing at the time of steeling, and carbon black was previously placed in a pan. For comparison, a test for melting ultra-low nitrogen pure iron according to the example of the present invention was also conducted under other conditions without using a carbon source for deoxidation and carburization at the time of steel production (comparison) Example). In both the inventive example and the comparative example, the carbon content in the molten steel at the time of steel output was 0.04% by mass or less.
表１に本発明例及び比較例の操業条件及び操業結果を示す。 Table 1 shows the operation conditions and operation results of the inventive examples and comparative examples.
比較例においては、出鋼後の取鍋内溶鋼の窒素濃度は０．００１７〜０．００３６質量％であるのに対して、本発明例では出鋼後の取鍋内溶鋼の窒素濃度は０．００１６質量％以下であった。また、ＲＨ真空脱ガス装置での精錬中の溶鋼中窒素の挙動から、本発明例の方が、吸窒量が少ないことがわかった。これらは何れも出鋼前に取鍋内に入れ置きした炭素源によって出鋼中及びＲＨ真空脱ガス装置での真空脱炭中に多量のＣＯガスが発生したことで、ＣＯガス気泡が溶鋼中の窒素を取り込んで脱窒を促進したためと考えられる。 In the comparative example, the nitrogen concentration of the molten steel in the ladle after steel is 0.0017 to 0.0036% by mass, whereas in the present invention example, the nitrogen concentration of the molten steel in the ladle after steel is 0. 0016% by mass or less. Moreover, from the behavior of nitrogen in molten steel during refining in the RH vacuum degassing apparatus, it was found that the amount of nitrogen absorption was smaller in the present invention example. In these cases, a large amount of CO gas was generated during the steel removal and during the vacuum decarburization by the RH vacuum degassing device due to the carbon source placed in the ladle before the steel output. This is thought to be because the nitrogen was taken in and promoted denitrification.
即ち、本発明を適用することで、窒素濃度が０．００１６質量％以下、燐濃度が０．００２５質量％以下の極低窒素純鉄を安定して溶製可能であることが確認できた。 That is, by applying the present invention, it has been confirmed that ultra-low nitrogen pure iron having a nitrogen concentration of 0.0016 mass% or less and a phosphorus concentration of 0.0025 mass% or less can be stably melted.
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