JP3606170B2 - Method for producing low nitrogen-containing chromium steel - Google Patents

Method for producing low nitrogen-containing chromium steel Download PDF

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Publication number
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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Prior art keywords
steel
slag
chromium
decarburization
low nitrogen
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JP2002020816A (en
Inventor
雄二郎 綱島
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Nippon Steel Corp
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Sumitomo Metal Industries Ltd
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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Cr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Al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Crを活性化させることによりCr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Cr発生の低減方法を開示している。
【0006】
さらに、生成したCr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Cr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Cr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Cr低減が必要であるが、Crの生成反応
2Cr+3/2 O→Cr
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Cr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Cr5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Cr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/SiO≦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 +SiO+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Cr≧5%、好ましくはCr≧ 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/SiO≦4.0 とする。好ましくは1.0 ≦CaO/SiO≦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+SiO+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Cr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Cr≧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】

Figure 0003606170
粗脱炭処理終了後のC含有量、スラグ組成、さらには炉体損傷の程度、スラグ滓化の程度、さらには還元材であるFeSi添加量、Arガス吹き込み量、そして酸素供給量について、結果を表2にまとめて示す。なお、FeSi添加量、Arガス吹き込み量、そして酸素供給量は、従来例のNo.1の場合を100 とした指数で示す。
【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】
Figure 0003606170
【0032】
【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]
Figure 0003606170
Results for C content, slag composition, degree of furnace body damage, degree of slag hatching, addition amount of FeSi as a reducing material, Ar gas injection amount, and oxygen supply amount after completion of rough decarburization treatment Are summarized in Table 2. The amount of FeSi added, the amount of Ar gas blown, and the amount of oxygen supplied were the same as those of the conventional example. The case of 1 is represented by an index of 100.
[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]
Figure 0003606170
[0032]
【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.

Claims (3)

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Cr5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Cr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。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 to 1 in a refining furnace placed under atmospheric pressure. Crude decarburization is performed to 0% by mass, and the obtained chromium-containing molten steel is produced in an undeoxidized or semi-deoxidized state, and then in a refining furnace placed under reduced pressure, Total [O] ≧ 150ppm and starts the vacuum degassing treatment at a Cr 2 O 3 5 wt% or more conditions in the slag, a method of manufacturing low-nitrogen-containing chromium steel which is characterized in that the reduction of Cr 2 O 3 in the slag, . 粗脱炭後のスラグ組成の塩基度が1.0 ≦CaO/SiO≦4.0 である請求項1記載の低窒素含クロム鋼の製造方法。The method for producing a low nitrogen chromium-containing steel according to claim 1, wherein the basicity of the slag composition after rough decarburization is 1.0 ≤CaO / SiO 2 ≤4.0. 粗脱炭処理中のスラグ組成がCaO +SiO+MgO ≧5質量%である、請求項1または2記載の低窒素含クロム鋼の製造方法。Slag composition of the crude decarburization in is CaO + SiO 2 + MgO ≧ 5% by weight, according to claim 1 or 2 method for producing a low nitrogen-containing chromium steel according.
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