JP3606170B2 - Method for producing low nitrogen-containing chromium steel - Google Patents
Method for producing low nitrogen-containing chromium steel Download PDFInfo
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- JP3606170B2 JP3606170B2 JP2000202763A JP2000202763A JP3606170B2 JP 3606170 B2 JP3606170 B2 JP 3606170B2 JP 2000202763 A JP2000202763 A JP 2000202763A JP 2000202763 A JP2000202763 A JP 2000202763A JP 3606170 B2 JP3606170 B2 JP 3606170B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、低窒素含クロム鋼の製造方法、特に高価なＦｅＳｉ等の還元剤の使用を抑制するとともに、必要な媒溶剤および低窒素化に必要である高価なＡｒの使用量を抑えることのできる低窒素含クロム鋼の製造方法に関する。
【０００２】
【従来の技術】
従来、含クロム溶鋼の溶製方法としては、高炉からの溶銑等にフェロクロム等のクロム合金鉄を投入して得た溶銑か、クロムを含んだスクラップを電気炉で溶解させて得た溶銑を転炉・ＡＯＤ 等の精錬炉にて精錬する方法がある。その際、炭素レベルは酸素を吹き付けることにより、窒素レベルについてはＡｒ等による脱ガスにて、それぞれ必要な濃度レベルにまで低下させ精錬している。さらに、必要によってはＶＯＤ 等も用いられている。
【０００３】
いずれの方法においても脱炭反応時においては、吹酸終了時にクロムが燃焼しＣｒ２Ｏ３ が発生するため、その還元にＦｅＳｉ等の還元剤を使用することが一般的である。しかし、ＦｅＳｉ等の還元剤は高価であるため、従来にあっても、その削減案が種々提示されている。
【０００４】
例えば、クロム燃焼の防止すなわち脱Ｃ効率の向上策として、特開平７−１７３５１５号公報では、脱炭中Ａｌ２Ｏ３ 濃度を１０〜２０％程度含有させることによりスラグの液相率を向上させ、スラグ中のＣｒ２Ｏ３ を活性化させることによりＣｒ２Ｏ３ での脱炭を促進させることを開示している。
【０００５】
特開平９−５９７０８ 号公報や特開平９−３５１７号公報では、フェロクロム等のクロム合金鉄添加前に溶鋼中の［％Ｃ］を２．５ 〜４．０ ％とし、溶鋼温度を１４５０〜１６００℃に昇温することを条件として脱炭反応の促進すなわちＣｒ２Ｏ３ 発生の低減方法を開示している。
【０００６】
さらに、生成したＣｒ２Ｏ３ 濃度の低減策として特開平８−１５７９３７号公報、特開平８−５３７０６ 号公報では、吹込ガス量を調整し、生成したスラグと溶鋼の攪拌強度を規定してスラグ中のＣｒ２Ｏ３ での脱炭方法を開示している。
【０００７】
しかし、いずれの方法においても、大気圧下で反応させる上ではＣｒ２Ｏ３ の発生量を抑えることは困難であり、さらに、低Ｎ鋼においてはスラグ−メタル攪拌のため多量のＡｒを使用する必要がある。
【０００８】
特開昭５６−１３９６１４号公報の開示する発明では、大気圧下で操業する精錬炉で還元剤を使用せず、減圧下にあるＶＯＤ において還元剤の使用を規定しているが、後述の低窒素鋼に必要な成分規制がなされていない。
【０００９】
脱窒のためには、低窒素鋼ほど大量の吹き込み用のＡｒの使用が必要となる。さらに精錬炉より取鍋へ出鋼中は大気に触れるため、出鋼中の吸窒も問題となっている。
【００１０】
これらの対策としてＶＯＤ 等の真空設備を用いた精錬方法も提案されている。しかし、高炉溶銑等の脱炭のように、高炭域での脱炭は、吹き上げ等の問題が発生するため、転炉またはＡＯＤ 等を用いる必要があり、根本的な問題解決にはいたっていない。
【００１１】
【発明が解決しようとする課題】
本発明の課題は、 ［Ｎ］：２００ｐｐｍ以下に制限した低窒素含クロム鋼のより安価で効率的な製造方法を開発することである。
【００１２】
より具体的には、本発明の課題は、低窒素含クロム鋼の精錬において、脱炭の時に吹き込まれた酸素により酸化した有価金属であるスラグ中のクロムを溶鋼へ回収する際、高価なＦｅＳｉ等の還元剤の使用を抑制でき、必要な媒溶剤の使用量を低減して精錬時に発生するスラグ量を抑制させ、さらに低窒素化に必要である高価なＡｒの使用量を抑えることのできる低窒素含クロム鋼の精錬方法を開発することである。
【００１３】
【課題を解決するための手段】
本発明者は、かかる課題を解決すべく、種々検討を重ね、次のような点に着目した。
【００１４】
還元剤の使用低減のためには、スラグ中のＣｒ２Ｏ３ 低減が必要であるが、Ｃｒ２Ｏ３ の生成反応
２Ｃｒ＋３／２ Ｏ２→Ｃｒ２Ｏ３
から考えると、酸素分圧の低減が有効である。
【００１５】
しかしながら、大気圧下での低減には限界がある。また低窒素鋼の製造においては、攪拌ガスとして吹き込み用の高価なＡｒを使用する必要があった。
しかも、真空設備の使用では、脱炭期の高炭素域では、吹き上げ等の問題が発生するため送酸速度の低下等で処理時間の延長が不可避であった。
【００１６】
ここに、本発明者は、未還元状態での吸窒量が極めて少ないことに着眼し、高炭素領域では大気圧下で脱炭可能な転炉またはＡＯＤ 等の精錬炉で粗脱炭を実施し、所定範囲にまで脱炭を行ってから、未還元のまま真空設備に移し替え、そこでスラグ組成を調整してから、攪拌用のＡｒガスの吹き込みを行い、ＦｅＳｉの添加によるＣｒ２Ｏ３ の還元を行うことで、［Ｎ］：２００ｐｐｍ以下、好ましくは［Ｎ］：１００ ｐｐｍ 以下という低窒素鋼の製造に際しても、ＦｅＳｉ等の還元剤および脱窒のためのＡｒ使用量の大幅な低減が可能となることを知り、本発明を完成した。
【００１７】
よって、本発明は次の通りである。
（１） 大気圧下での精錬工程と、減圧下での精錬工程を備えた低窒素含クロム鋼の製造方法であって、大気圧下に置かれた精錬炉にてＣ含有量０．００５ 〜１．０ 質量％にまで粗脱炭を行い、得られた含クロム溶鋼を未脱酸または半脱酸の状態で出鋼し、次いで減圧下に置かれた精錬炉で、鋼中Ｔｏｔａｌ［Ｏ］≧１５０ｐｐｍ、かつスラグ中のＣｒ２Ｏ３ ５質量％以上の条件下で真空脱ガス処理を開始し、スラグ中のＣｒ２Ｏ３ の還元を行うことを特徴とする低窒素含クロム鋼の製造方法。
（２） 粗脱炭後のスラグ組成の塩基度が１．０ ≦ＣａＯ／ＳｉＯ２≦４．０ である上記（１） 記載の低窒素含クロム鋼の製造方法。
（３） 粗脱炭処理中のスラグ組成がＣａＯ ＋ＳｉＯ２＋ＭｇＯ ≧５質量％である、上記（１） または（２） 記載の低窒素含クロム鋼の製造方法。
【００１８】
【発明の実施の形態】
このように本発明によれば、高炭素領域では大気圧下で精錬を行い、未還元のまま真空設備に移し替え、真空下で還元処理を行うのである。
【００１９】
本発明においてそれぞれの処理条件を上述のように限定した理由について説明する。
本発明において大気圧下での粗脱炭処理を行うのは従来のＣｒ含有溶銑であればよく、特に制限はなく、また粗脱炭処理それ自体も従来法にしたがって行えばよい。
【００２０】
本発明では、このような粗脱炭処理は溶鋼中のＣ含有量が０．００５ 〜１．０ 質量％になるまで行う。Ｃ：１．０質量％より高い炭素域で大気圧下での脱炭を終了すると、真空処理に際しての溶鋼の吹き上げを防止できないことから、Ｃ：１．０質量％以下にまで脱炭を行う。
【００２１】
一方、本発明によれば、粗脱炭後の真空処理設備での脱窒においては、脱窒促進にはＣＯガスを発生させることが処理時間の短縮につながる。そのため、例えば真空処理後の鋼中［％Ｎ］≦２００ｐｐｍの鋼種においては、粗脱炭後の鋼中炭素をある程度残す必要がある。本発明ではこのときの下限をＣ：０．００５％ と規定する。好ましくは、Ｃ：０ ．１ 〜１．０ ％の範囲で粗脱炭処理を終了する。
【００２２】
また、脱窒促進にはＣＯガスを発生させることが処理時間の短縮に繋がるが、ＣＯガスを発生させる酸素源として、鋼中ｔｏｔａｌ［Ｏ］≧１５０ｐｐｍ かつスラグ中のＣｒ２Ｏ３ ≧５％、好ましくはＣｒ２Ｏ３ ≧ １５％とすることで真空脱ガス装置での酸素原単位低減を図ることができる。好ましい鋼中ｔｏｔａｌ［Ｏ］は、１５０ 〜３００ ｐｐｍ である。
【００２３】
本発明の好適態様にあっては、さらに、上述のような粗脱炭後のスラグ組成を、１．０ ≦ＣａＯ／ＳｉＯ２≦４．０ とする。好ましくは１．０ ≦ＣａＯ／ＳｉＯ２≦３．０ である。
これは、還元処理時間短縮のためスラグを速やかに滓化させる必要があるが、その範囲を規定するものである。また、含クロム鋼、特にステンレス鋼の脱硫は還元期に実施するが、従来は粗脱炭後、真空処理後に、二回の還元処理 （脱硫処理） を実施していたが、本発明により還元 （脱硫） は一回のみとなるため脱硫能力確保の観点より塩基度の下限を１．０ に規定する。
【００２４】
本発明の別の好適態様にあっては、粗脱炭後のスラグにおいて、ＣａＯ＋ＳｉＯ２＋ＭｇＯ≧５％と規定するが、これは、脱炭精錬炉の炉体保護のため下限を設定した。
粗脱炭スラグはＣｒ２Ｏ３ の還元熱により溶鋼温度が減少するため、全量または、一部の粗脱炭スラグを排滓してもよいし、ＣＯガスの発生源として全量持ち越して粗溶鋼と共に真空処理を施しても良い。
【００２５】
場合によりＡｌ、Ｓｉ含有物質または、蛍石等のスラグ滓化剤を添加することにより、粗脱炭スラグを滓化させることが可能となり、より確実に真空精錬の還元時、クロム回収が実施可能となる。
【００２６】
本発明において、上述のような粗脱炭処理に続いて真空脱ガス処理を行うが、開始時に鋼中Ｔｏｔａｌ［Ｏ］≧１５０ｐｐｍ、スラグ中のＣｒ２Ｏ３ ≧５質量％の条件を満足する限り、より好ましくはさらにスラグ塩基度１．０ 〜４．０ である限り、その真空脱ガス処理は、例えばＶＯＤ 炉を使い従来のままであっても良く、特に制限されない。
【００２７】
【実施例】
精錬炉としてＡＯＤ 炉を使用し、真空処理装置としてＶＯＤ を使用した。
本例においては、下記組成の溶銑を用意し、最初大気圧下でのＡＯＤ を用いて粗脱炭を行い、次いで真空度４ＴｏｒｒのＶＯＤ 炉を使って真空脱ガス処理を行い、低窒素含クロム鋼の製造を行った。
【００２８】
なお、粗脱炭、真空脱ガス処理の合計処理時間は、ほぼ１００ 〜２００ 分間であって、これは、従来例と実質同様な処理時間である。粗脱炭後の成分組成を表１に示す。
【００２９】
【表１】
【００３０】
なお、表２において、炉体溶損は、○：溶鋼、△：普通、×：悪化の３段階評価で示す。また、スラグ滓化も、○：滓化良好、△：通常滓化、×：滓化不良の３段階評価で示す。
【００３１】
【表２】
【発明の効果】
本発明を用いることにより、Ｎ＜２００ｐｐｍ の低窒素含クロム鋼の溶製において、炉体およびスラグ滓化量 （Ｃｒ回収） を悪化させることなくＦｅＳｉ、Ａｒ原単位が低減可能となり、製造原価を大きく低減させることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention is a method for producing a low nitrogen chromium-containing steel, and in particular, suppresses the use of expensive reducing agents such as FeSi, and suppresses the required solvent and the amount of expensive Ar required for reducing nitrogen. The present invention relates to a method for producing low nitrogen-containing chromium steel.
[0002]
[Prior art]
Conventionally, as a method for producing chromium-containing molten steel, hot metal obtained by introducing chromium alloy iron such as ferrochrome into hot metal from a blast furnace, or hot metal obtained by melting chromium-containing scrap in an electric furnace is used. There is a method of refining in a refining furnace such as a furnace or AOD. At that time, the carbon level is refined by blowing oxygen and reducing the nitrogen level to a necessary concentration level by degassing with Ar or the like. Furthermore, VOD or the like is also used if necessary.
[0003]
In any of the methods, during the decarburization reaction, chromium burns at the end of the blowing acid and Cr 2 O 3 is generated. Therefore, it is common to use a reducing agent such as FeSi for the reduction. However, since reducing agents such as FeSi are expensive, various proposals for reducing them have been presented.
[0004]
For example, as a measure for preventing chromium combustion, that is, improving the de-C efficiency, Japanese Patent Application Laid-Open No. 7-173515 improves the liquid phase rate of slag by containing about 10 to 20% of the Al 2 O 3 concentration during decarburization. , discloses that to promote the decarburization by Cr 2 O 3 by activating the Cr 2 O 3 in the slag.
[0005]
In JP-A-9-59708 and JP-A-9-3517, before addition of chromium alloy iron such as ferrochrome, [% C] in the molten steel is set to 2.5 to 4.0% and the molten steel temperature is set to 1450 to 1600. It discloses a method for promoting the decarburization reaction, that is, reducing the generation of Cr 2 O 3 under the condition that the temperature is raised to ° C.
[0006]
Furthermore, as a measure for reducing the concentration of the produced Cr 2 O 3 , JP-A-8-157937 and JP-A-8-53706 regulate the amount of blown gas and regulate the agitation strength of the produced slag and molten steel to define the slag. A decarburization method with Cr 2 O 3 therein is disclosed.
[0007]
However, in either method, it is difficult to suppress the amount of Cr 2 O 3 generated when the reaction is performed under atmospheric pressure, and a large amount of Ar is used for slag-metal stirring in low-N steel. There is a need.
[0008]
In the invention disclosed in Japanese Patent Laid-Open No. 56-139614, a reducing agent is not used in a refining furnace operating at atmospheric pressure, and the use of a reducing agent is prescribed in VOD under reduced pressure. The component regulation required for nitrogen steel is not made.
[0009]
For denitrification, it is necessary to use a larger amount of Ar for low nitrogen steel. Furthermore, since the steel is exposed to the atmosphere from the smelting furnace to the ladle, nitrogen absorption during the steel is also a problem.
[0010]
As a countermeasure against these, a refining method using a vacuum equipment such as VOD has been proposed. However, decarburization in blast furnace areas, such as decarburization of blast furnace hot metal, causes problems such as blowing up, so it is necessary to use a converter or AOD, etc., and the fundamental problem has not been solved. .
[0011]
[Problems to be solved by the invention]
The object of the present invention is to develop a cheaper and more efficient production method of low nitrogen-containing chromium steel limited to [N]: 200 ppm or less.
[0012]
More specifically, an object of the present invention is to provide an expensive FeSi when recovering chromium in slag, which is a valuable metal oxidized by oxygen blown at the time of decarburization, in refining low nitrogen chromium steel to molten steel. It is possible to suppress the use of a reducing agent, etc., to reduce the amount of slag generated during refining by reducing the amount of necessary solvent used, and to suppress the amount of expensive Ar necessary for reducing nitrogen. The aim is to develop a method for refining low nitrogen-containing chromium steel.
[0013]
[Means for Solving the Problems]
The present inventor has made various studies in order to solve such problems, and has focused on the following points.
[0014]
In order to reduce the use of the reducing agent, it is necessary to reduce Cr 2 O 3 in the slag, but the formation reaction of Cr 2 O 3 2Cr + 3/2 O 2 → Cr 2 O 3
Therefore, it is effective to reduce the oxygen partial pressure.
[0015]
However, there is a limit to the reduction under atmospheric pressure. In the production of low nitrogen steel, it was necessary to use expensive Ar for blowing as a stirring gas.
In addition, in the use of vacuum equipment, problems such as blowing up occur in the high carbon region during the decarburization period, and therefore it is inevitable to extend the treatment time due to a decrease in the acid feed rate.
[0016]
Here, the present inventor noticed that the amount of nitrogen absorption in the unreduced state is extremely small, and in the high carbon region, rough decarburization was carried out in a refining furnace such as a converter or AOD that can be decarburized at atmospheric pressure. Then, after decarburizing to a predetermined range, it is transferred to vacuum equipment without reduction, and after adjusting the slag composition, Ar gas for stirring is blown, and Cr 2 O 3 is added by adding FeSi. In the production of a low nitrogen steel with [N]: 200 ppm or less, preferably [N]: 100 ppm or less, a reduction in the amount of Ar used for denitrification and a reducing agent such as FeSi is achieved. The present invention has been completed.
[0017]
Therefore, the present invention is as follows.
(1) A method for producing a low nitrogen chromium-containing steel comprising a refining step under atmospheric pressure and a refining step under reduced pressure, wherein the C content is 0.005 in a refining furnace placed under atmospheric pressure. Crude decarburization is performed to ˜1.0% by mass, and the obtained chromium-containing molten steel is produced in a non-deoxidized or semi-deoxidized state, and then in a refining furnace placed under reduced pressure, the total [ O] ≧ 150 ppm, and start the vacuum degassing treatment at a Cr 2 O 3 5 wt% or more conditions in the slag, low nitrogen-containing chromium steel which is characterized in that the reduction of Cr 2 O 3 in the slag Manufacturing method.
(2) Crude above basicity of slag composition after decarburization is 1.0 ≦ CaO / SiO 2 ≦ 4.0 (1) method for producing a low nitrogen-containing chromium steel according.
(3) Slag Composition of crude decarburization in is CaO + SiO 2 + MgO ≧ 5% by weight, the (1) or (2) The method of producing low-nitrogen chromium-containing steel according.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
As described above, according to the present invention, refining is performed under atmospheric pressure in the high carbon region, transferred to vacuum equipment without reduction, and reduction processing is performed under vacuum.
[0019]
The reason why each processing condition is limited as described above in the present invention will be described.
In the present invention, the crude decarburization treatment under atmospheric pressure may be performed with any conventional Cr-containing hot metal, and is not particularly limited, and the crude decarburization treatment itself may be performed according to the conventional method.
[0020]
In the present invention, such rough decarburization treatment is performed until the C content in the molten steel becomes 0.005 to 1.0 mass%. C: When decarburization under atmospheric pressure is completed in a carbon region higher than 1.0% by mass, it is not possible to prevent the molten steel from being blown up during vacuum processing, so C: 1.0% by mass or less is decarburized. .
[0021]
On the other hand, according to the present invention, in denitrification in a vacuum processing facility after rough decarburization, generating CO gas for promoting denitrification leads to a reduction in processing time. Therefore, for example, in a steel type of [% N] ≦ 200 ppm in steel after vacuum treatment, it is necessary to leave some carbon in the steel after rough decarburization. In the present invention, the lower limit is defined as C: 0.005%. Preferably, C: 0. The rough decarburization process is finished in the range of 1 to 1.0%.
[0022]
Further, although CO gas is generated for promoting denitrification, the processing time is shortened. However, as an oxygen source for generating CO gas, total [O] ≧ 150 ppm in steel and Cr 2 O 3 in slag ≧ 5% Preferably, by setting Cr 2 O 3 ≧ 15%, it is possible to reduce the oxygen intensity in the vacuum degassing apparatus. A preferable total [O] in the steel is 150 to 300 ppm.
[0023]
In the preferred embodiment of the present invention, the slag composition after rough decarburization as described above is set to 1.0 ≦ CaO / SiO 2 ≦ 4.0. Preferably, 1.0 ≦ CaO / SiO 2 ≦ 3.0.
This requires that the slag be hatched quickly in order to shorten the reduction treatment time, but defines the range. In addition, desulfurization of chromium-containing steel, especially stainless steel, is carried out during the reduction phase. Conventionally, after the rough decarburization and vacuum treatment, two reduction treatments (desulfurization treatment) have been carried out. Since (desulfurization) is performed only once, the lower limit of basicity is defined as 1.0 from the viewpoint of ensuring desulfurization capacity.
[0024]
In another preferred embodiment of the present invention, CaO + SiO 2 + MgO ≧ 5% is defined in the slag after rough decarburization, but this is set to a lower limit for protecting the furnace body of the decarburization refining furnace.
Since the temperature of the molten steel decreases due to the reduction heat of Cr 2 O 3 in the coarse decarburized slag, the entire amount or a part of the coarse decarburized slag may be discharged, or the entire amount is carried over as a CO gas generation source. In addition, vacuum treatment may be performed.
[0025]
In some cases, it is possible to hatch crude decarburized slag by adding slag fading agents such as Al, Si-containing materials or fluorite, and more reliably recover chromium during the reduction of vacuum refining. It becomes.
[0026]
In the present invention, vacuum degassing treatment is performed following the above rough decarburization treatment, and the conditions of Total [O] ≧ 150 ppm in steel and Cr 2 O 3 ≧ 5 mass% in slag are satisfied at the start. As long as the slag basicity is 1.0 to 4.0 as long as possible, the vacuum degassing treatment may be performed as is conventionally using, for example, a VOD furnace, and is not particularly limited.
[0027]
【Example】
An AOD furnace was used as the refining furnace, and VOD was used as the vacuum processing apparatus.
In this example, hot metal having the following composition is prepared, first, rough decarburization is performed using AOD under atmospheric pressure, and then vacuum degassing is performed using a VOD furnace having a vacuum degree of 4 Torr. Steel was produced.
[0028]
In addition, the total processing time of rough decarburization and vacuum degassing is approximately 100 to 200 minutes, which is substantially the same processing time as the conventional example. Table 1 shows the component composition after rough decarburization.
[0029]
[Table 1]
[0030]
In Table 2, the melting loss of the furnace body is indicated by a three-step evaluation of ○: molten steel, Δ: normal, and x: deterioration. In addition, slag hatching is also indicated by a three-stage evaluation of ○: good hatching, Δ: normal hatching, x: poor hatching.
[0031]
[Table 2]
【The invention's effect】
By using the present invention, it is possible to reduce the basic unit of FeSi and Ar without deteriorating the furnace body and the amount of slag hatching (Cr recovery) in the production of low nitrogen-containing chromium steel with N <200 ppm. It can be greatly reduced.
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| CN104486986B (en) | 2012-07-26 | 2018-06-01 | 德普伊辛迪斯制品公司 | Continuous videos in light deficiency environment |
| EP2877080B1 (en) | 2012-07-26 | 2020-07-22 | DePuy Synthes Products, Inc. | Ycbcr pulsed illumination scheme in a light deficient environment |
| JP2016519591A (en) | 2013-03-15 | 2016-07-07 | オリーブ・メディカル・コーポレイションＯｌｉｖｅ Ｍｅｄｉｃａｌ Ｃｏｒｐｏｒａｔｉｏｎ | Super-resolution and color motion artifact correction in pulse color imaging system |
| US9777913B2 (en) | 2013-03-15 | 2017-10-03 | DePuy Synthes Products, Inc. | Controlling the integral light energy of a laser pulse |
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