JPH11229027A - Method for denitrificating chromium-containing molten steel - Google Patents
Method for denitrificating chromium-containing molten steelInfo
- Publication number
- JPH11229027A JPH11229027A JP4634298A JP4634298A JPH11229027A JP H11229027 A JPH11229027 A JP H11229027A JP 4634298 A JP4634298 A JP 4634298A JP 4634298 A JP4634298 A JP 4634298A JP H11229027 A JPH11229027 A JP H11229027A
- Authority
- JP
- Japan
- Prior art keywords
- molten steel
- decarburization
- rate
- oxygen
- chromium
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Landscapes
- Treatment Of Steel In Its Molten State (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、減圧雰囲気下の精
錬において行う含クロム溶鋼の脱窒方法に関するもので
あり、特にＶＯＤ（真空脱ガス）処理で低窒素含クロム
鋼を溶製するのに適した脱窒方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for denitrifying chromium-containing molten steel in refining under reduced pressure atmosphere, and more particularly to a method for producing low nitrogen chromium-containing steel by VOD (vacuum degassing) treatment. It relates to a suitable denitrification method.
【０００２】[0002]
【従来の技術】含クロム溶鋼の脱窒は、従来から一般的
に、溶鋼中の脱炭反応で発生するＣＯ気泡の激しいボイ
リングを利用して行われている。これは、ＣＯ気泡に窒
素がくっついて逃げる現象を利用するものであり、脱窒
を十分進行させるには脱窒処理前の溶鋼中にある程度高
濃度の炭素が含まれていることが必要である。2. Description of the Related Art Conventionally, denitrification of chromium-containing molten steel has been generally carried out by utilizing intense boiling of CO bubbles generated by a decarburization reaction in molten steel. This utilizes the phenomenon in which nitrogen sticks to CO bubbles and escapes. In order for denitrification to proceed sufficiently, it is necessary that molten steel before denitrification contains a certain high concentration of carbon. .
【０００３】しかし、溶鋼中の炭素濃度（［％Ｃ］）が
高いということは、脱炭にそれだけ長時間を要し、往々
精錬時間が延びることになる。一方、酸素吹き込み速度
をいたずらに大きくすることは過度のボイリングによる
溶鋼のオーバーフローを招き、好ましくない。However, a high carbon concentration ([% C]) in molten steel requires a long time for decarburization, and often increases the refining time. On the other hand, unnecessarily increasing the oxygen blowing speed undesirably causes the molten steel to overflow due to excessive boiling.
【０００４】[0004]
【発明が解決しようとする課題】低窒素鋼を溶製する際
の精錬時間の延長を回避する方法として、例えば特開昭
60−26611号公報には、ＶＯＤのみで行っていた脱窒を
転炉にも分担させる方法が提案されている。しかしこの
方法においても、ＶＯＤにおける脱窒そのものに関して
より一層の効率化を図る試みはなされておらず、更なる
生産性改善の余地が残されているのが現状である。そこ
で本発明は、脱炭に消費される酸素と供給する酸素の収
支バランスを適切にコントロールすることによって、よ
り低い初期炭素濃度値においても安定的に脱窒率を高め
ることができる効率的な脱窒方法を提供することを目的
とする。As a method for avoiding the extension of the refining time when smelting low nitrogen steel, for example, Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open No. 60-26611 proposes a method in which denitrification performed only by VOD is shared by a converter. However, even in this method, no attempt has been made to further increase the efficiency of denitrification itself in VOD, and there is currently room for further improvement in productivity. Therefore, the present invention provides an efficient denitrification method capable of stably increasing the denitrification rate even at a lower initial carbon concentration value by appropriately controlling the balance between the oxygen consumed for decarburization and the oxygen supplied. It is intended to provide a nitriding method.
【０００５】[0005]
【課題を解決するための手段】上記目的を達成するため
に、請求項１の発明は、閉鎖容器中で真空排気しながら
酸素を吹き付けて脱炭を行う含クロム溶鋼の精錬におい
て脱炭反応のボイリングを利用して該溶鋼の脱窒を行う
に際し、酸素供給速度（Nm3／h）を、下記（１）式の脱
炭反応における酸素消費速度（Nm3／h）より小さくなる
ようにコントロールしながら酸素を吹き付ける、含クロ
ム溶鋼の脱窒方法である。 ２Ｃ＋Ｏ2→２ＣＯ ・・（１） ここで、「酸素消費速度」とは当該脱炭中において脱炭
反応の進行に伴って変化する酸素消費速度を意味し、
「Nm3」は標準状態での気体の体積（m3）である。Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 is directed to a decarburization reaction in the refining of chromium-containing molten steel in which oxygen is blown in a closed vessel while evacuating and decarburizing. When denitrifying the molten steel using boiling, the oxygen supply rate (Nm 3 / h) is controlled to be smaller than the oxygen consumption rate (Nm 3 / h) in the decarburization reaction of the following formula (1). This is a method of denitrifying chromium-containing molten steel while blowing oxygen. 2C + O 2 → 2CO (1) Here, “oxygen consumption rate” means an oxygen consumption rate that changes with the progress of the decarburization reaction during the decarburization,
“Nm 3 ” is the volume of gas (m 3 ) in the standard state.
【０００６】請求項２の発明は、請求項１の発明におい
て、酸素消費速度（Nm3／h）を特に、予め定めてある脱
炭速度（ppm／min）の予想経時変化パターンを用いて算
出したものに規定したものである。ここで、「脱炭速度
（ppm／min）の予想経時変化パターン」とは精錬条件に
応じて予め実験や過去の経験から求めておいた脱炭速度
−時間曲線などを意味する。（１）式より、１モルのＣ
を脱炭するのに必要なＯ2は１／２モルであるから、あ
る時点での脱炭速度（ppm／min）が判ればそれに対応す
る酸素消費速度（Nm3／h）は単位を換算して容易に求め
ることができる。According to a second aspect of the present invention, in the first aspect of the present invention, the oxygen consumption rate (Nm 3 / h) is calculated using an expected time-dependent change pattern of the predetermined decarburization rate (ppm / min). It is specified in what was done. Here, the “expected time-dependent change pattern of the decarburization rate (ppm / min)” means a decarburization rate-time curve determined in advance from experiments or past experiences according to the refining conditions. From formula (1), one mole of C
O 2 required for decarburizing is 1/2 mole, so if the decarburization rate (ppm / min) at a certain point is known, the corresponding oxygen consumption rate (Nm 3 / h) is converted into units. Can be easily obtained.
【０００７】請求項３の発明は、請求項１の発明におい
て、酸素消費速度（Nm3／h）を特に、当該脱炭中に真空
排気中のガス成分を分析して求めた脱炭速度（ppm／mi
n）の値から算出したものに規定したものである。According to a third aspect of the present invention, in the first aspect of the invention, the oxygen consumption rate (Nm 3 / h) is determined by analyzing a gas component in the vacuum exhaust during the decarburization. ppm / mi
It is defined as calculated from the value of n).
【０００８】請求項４の発明は、酸素供給速度（Nm3／
h）のコントロール手法を具体的に示したものである。
すなわち、脱炭中に、下記（２）式を用いて目標酸素供
給速度Ｑ（Nm3／h）を連続的にまたは繰り返し算出し、
酸素供給速度（Nm3／h）を該目標酸素供給速度Ｑになる
ようにコントロールするものである。 Ｑ＝ｎ×Ｓ×Ｗ×10-6×(22.4／24)×60 ・・（２） ただし、ｎは酸素供給速度指数であって0.5以上１未満
の範囲にある定数、Ｓは脱炭速度（ppm／min）を表す変
数、Ｗは溶鋼質量（kg）を表す定数である。According to the invention of claim 4, the oxygen supply rate (Nm 3 /
This specifically illustrates the control method of h).
That is, during decarburization, the target oxygen supply rate Q (Nm 3 / h) is continuously or repeatedly calculated using the following equation (2).
The oxygen supply rate (Nm 3 / h) is controlled so as to reach the target oxygen supply rate Q. Q = n × S × W × 10 −6 × (22.4 / 24) × 60 (2) where n is an oxygen supply rate index and is a constant in the range of 0.5 or more and less than 1, and S is a decarburization rate. (Ppm / min), and W is a constant representing the mass (kg) of molten steel.
【０００９】請求項４の発明では、脱炭の進行に伴って
変化する脱炭速度（ppm／min）の値を連続的にまたは繰
り返し求めながら逐次（２）式によって目標酸素供給速
度Ｑを算出し、ほぼリアルタイムで酸素供給速度（Nm3
／h）を目標酸素供給速度Ｑに設定する。（２）式にお
ける酸素供給速度指数ｎを１未満の定数とした点が特徴
であり、これにより脱炭の進行に伴う脱炭速度の低下に
酸素供給速度をうまく追随させて、酸素の供給・消費の
収支バランスを改善して過剰酸素の低減を図ろうという
ものである。According to the fourth aspect of the present invention, the target oxygen supply rate Q is calculated by the equation (2) while continuously or repeatedly obtaining the value of the decarburization rate (ppm / min) that changes with the progress of decarburization. And the oxygen supply rate (Nm 3
/ H) is set as the target oxygen supply rate Q. The feature is that the oxygen supply rate index n in the equation (2) is set to a constant less than 1. This allows the oxygen supply rate to properly follow the decrease in the decarburization rate accompanying the progress of decarburization. The aim is to improve the balance of consumption and reduce excess oxygen.
【００１０】請求項５の発明は、請求項４の発明におい
て、（２）式の脱炭速度Ｓを特に、当該脱炭中に真空排
気中のガス成分を分析して求めたものに規定したもので
ある。A fifth aspect of the present invention is the invention according to the fourth aspect, wherein the decarburization rate S in the formula (2) is defined as a value determined by analyzing a gas component in vacuum evacuation during the decarburization. Things.
【００１１】請求項６の発明は、請求項４または５の発
明において、（２）式の酸素供給速度指数ｎを特に0.8
以上0.95以下の範囲にある定数としたものである。According to a sixth aspect of the present invention, in the fourth or fifth aspect, the oxygen supply rate index n of the formula (2) is particularly set to 0.8.
This is a constant in the range of 0.95 or less.
【００１２】請求項７の発明は、請求項４，５または６
の発明において、酸素供給速度のコントロールを特に、
真空排気開始後に閉鎖容器内の圧力が300Torr以下にな
ってから開始し、溶鋼中の炭素濃度が0.15質量％以下に
減少してから終了するように規定したものである。The invention of claim 7 is the invention of claim 4, 5 or 6.
In the invention of the present invention, particularly the control of the oxygen supply rate,
It is defined that the process is started after the pressure in the closed vessel becomes 300 Torr or less after the evacuation is started, and is finished after the carbon concentration in the molten steel is reduced to 0.15% by mass or less.
【００１３】[0013]
【発明の実施の形態】含クロム溶鋼における脱窒反応
は、２Ｎ→Ｎ2(ｇ)、の反応であり、これはＣ−Ｏ反応
（脱炭反応）の激しいボイリングによって生じる。その
ため、脱窒処理前の［％Ｃ］を高くすることがトータル
的に生成するＣＯ気泡の量を多くし、脱窒促進には有利
となる。しかし前述のように、処理前の［％Ｃ］を高く
すれば往々脱炭時間が延び、好ましくない。もし、実操
業において脱窒反応そのものをより効率的に進行させる
方法があれば、同じ処理前［％Ｃ］値でも一層低窒素の
鋼が得られるであろうし、目標窒素濃度が同じなら一層
低い処理前［％Ｃ］値にて短時間で脱炭を終了できるで
あろう。BEST MODE FOR CARRYING OUT THE INVENTION The denitrification reaction in chromium-containing molten steel is a reaction of 2N → N 2 (g), which is caused by intense boiling of the CO reaction (decarburization reaction). Therefore, increasing [% C] before the denitrification treatment increases the total amount of CO bubbles generated, which is advantageous for promoting denitrification. However, as described above, if [% C] before the treatment is increased, the decarburization time is often extended, which is not preferable. If there is a method to allow the denitrification reaction to proceed more efficiently in actual operation, a steel with lower nitrogen will be obtained even at the same [% C] value before treatment, and a lower nitrogen if the target nitrogen concentration is the same. Decarburization could be completed in a short time at the pre-treatment [% C] value.
【００１４】本発明者らは、実操業において従来よりも
効率的に脱窒反応を促進させる手段を種々検討し、その
検討の過程で、溶鋼中の過剰酸素の低減が非常に有効で
あることを知見した。酸素は溶鋼中において界面活性元
素として働くから、溶鋼中の酸素濃度が高くなると脱窒
には不利となる。The present inventors have studied various means for promoting the denitrification reaction more efficiently than in the past in actual operation, and in the course of the study, it has been found that the reduction of excess oxygen in molten steel is very effective. Was found. Oxygen acts as a surface active element in the molten steel, so that an increase in the oxygen concentration in the molten steel is disadvantageous for denitrification.
【００１５】図１は、ＶＯＤにおいて十分に酸素を供給
したときの溶鋼中炭素濃度［％Ｃ］および脱炭速度（pp
m／min）の一般的な経時変化を定性的に表したものであ
る。［％Ｃ］はＣ−Ｏ反応の進行に伴い連続的に減少す
る。脱炭速度は［％Ｃ］や溶鋼温度の影響を受けて変化
するが、通常、真空引き開始後しばらくして最大にな
り、その後、時間の経過とともに低下する。脱炭は実質
的に次式、 ２Ｃ＋Ｏ2→２ＣＯ ・・（１） の反応であるから、脱炭速度（ppm／min）の変化は酸素
消費速度の変化を意味する。溶鋼中に過剰酸素を残さな
いことだけが目的なら、酸素供給速度を酸素消費速度よ
り十分に小さい値に設定すればよい。しかしそれでは脱
炭反応速度自体が酸素供給速度に律速されてしまい、効
率的な脱窒を図ろうとする本発明の目的は達成できな
い。そこで本発明では、刻々変化する脱炭速度（すなわ
ち酸素消費速度）に応じて、適切な酸素供給速度を設定
する。ただし、そのコントロールをあまり過剰に高精度
化することは、コスト面等において実操業での適用を難
しくする。したがって、従来の設備を用いて実施できる
簡便な方法を提供することが望まれる。FIG. 1 shows the carbon concentration in molten steel [% C] and the decarburization rate (pp
(m / min) qualitatively. [% C] continuously decreases as the CO reaction proceeds. The decarburization rate changes under the influence of [% C] and the temperature of the molten steel, but usually reaches its maximum some time after the start of evacuation, and thereafter decreases with time. Since decarburization is substantially a reaction of the following formula: 2C + O 2 → 2CO (1), a change in the decarburization rate (ppm / min) means a change in the oxygen consumption rate. If the only purpose is not to leave excess oxygen in the molten steel, the oxygen supply rate may be set to a value sufficiently smaller than the oxygen consumption rate. However, in that case, the decarburization reaction rate itself is limited by the oxygen supply rate, and the object of the present invention for achieving efficient denitrification cannot be achieved. Therefore, in the present invention, an appropriate oxygen supply rate is set according to the decarburizing rate (ie, the oxygen consumption rate) that changes every moment. However, making the control too high in accuracy makes it difficult to apply it in actual operation in terms of cost and the like. It is therefore desirable to provide a simple method that can be implemented using conventional equipment.
【００１６】本発明者らは、脱炭速度（ppm／min）の経
時変化パターンに着目した。すなわち脱炭速度は、真空
引き開始後しばらくして最大になり、その後、時間の経
過とともに低下する。脱炭速度が低下する領域は脱炭時
間の大部分を占める。そのため、脱炭速度が低下しつつ
あるときの酸素供給速度のコントロールが、過剰酸素を
低減するうえで極めて重要となる。The present inventors have paid attention to the time-dependent change pattern of the decarburization rate (ppm / min). That is, the decarburization speed reaches its maximum some time after the start of evacuation, and thereafter decreases with time. The region where the decarburization rate is low accounts for most of the decarburization time. Therefore, control of the oxygen supply rate when the decarburization rate is decreasing is extremely important in reducing excess oxygen.
【００１７】脱炭速度が低下しているときには酸素消費
速度が時々刻々低下しているので、例えばある時点でそ
の時の酸素消費速度を求め、それに等しい値に酸素供給
速度を設定しても、その値で実際に酸素が供給される時
点ではすでに「酸素消費速度＜酸素供給速度」となり、
酸素は過剰となる。連続的に酸素供給速度をコントロー
ルしたとしても、酸素消費速度算出と酸素供給のタイム
ラグにより酸素供給が過大になる。酸素消費速度を繰り
返し求め、段階的に酸素供給速度を再設定するようなコ
ントロールではなおさらである。When the decarburization rate is decreasing, the oxygen consumption rate is decreasing every moment. For example, even if the oxygen consumption rate at that time is obtained and the oxygen supply rate is set to a value equal thereto, the At the time when oxygen is actually supplied by the value, "oxygen consumption rate <oxygen supply rate" already holds,
Oxygen becomes excess. Even if the oxygen supply rate is controlled continuously, the oxygen supply becomes excessive due to the calculation of the oxygen consumption rate and the time lag of the oxygen supply. This is even more so in a control in which the oxygen consumption rate is repeatedly obtained and the oxygen supply rate is reset stepwise.
【００１８】閉鎖容器中で真空排気しながら酸素を吹き
付けて脱炭を行う含クロム溶鋼の精錬においては、通
常、脱炭速度は増加したり低下したりを繰り返すのでは
なく、図１のようにある時点以降一様に低下する。この
ような脱炭速度の特性を活かすことを考慮した結果、次
式、 ２Ｃ＋Ｏ2→２ＣＯ ・・（１） の脱炭反応におけるその時点での酸素消費速度より小さ
くなるように酸素供給速度（Nm3／h）をコントロールし
ながら酸素を吹き付けることによって、脱炭速度の変化
（酸素消費速度の変化）に追随して過剰な酸素供給を防
止することができた。その結果、溶鋼中の酸素濃度は低
く維持され、脱窒反応が効果的に促進されるのである。In the refining of molten chromium-containing steel in which decarburization is performed by blowing oxygen while evacuating in a closed vessel, the decarburization rate does not usually increase or decrease, as shown in FIG. It decreases uniformly after a certain point. As a result of taking advantage of such characteristics of the decarburization rate, the oxygen supply rate (Nm) is set to be smaller than the oxygen consumption rate at that time in the decarburization reaction of the following formula: 2C + O 2 → 2CO (1) By spraying oxygen while controlling 3 / h), it was possible to follow the change in the decarburization rate (change in the oxygen consumption rate) and prevent an excessive supply of oxygen. As a result, the oxygen concentration in the molten steel is kept low, and the denitrification reaction is effectively promoted.
【００１９】このようなコントロールは精錬中に実際の
酸素消費量の変化を求めて、そのデータに基づいて行う
のが、精度を高めるうえで有利である。しかし、酸素消
費量を計測する設備がない場合や、溶鋼の初期酸素濃
度，初期炭素濃度，温度，目標組成などの条件が安定し
ているような場合には、予め実験等によって求めておい
た脱炭速度（ppm／min）の予想経時変化パターンを用い
て精錬中の酸素消費速度を予測し、上記のように酸素供
給速度（Nm3／h）をコントロールしてもよい。この方法
によっても、実用上問題のない精度で過剰酸素を抑制す
ることが可能である。It is advantageous to obtain the actual change in oxygen consumption during refining and to perform such control based on the data. However, when there is no equipment for measuring oxygen consumption, or when conditions such as initial oxygen concentration, initial carbon concentration, temperature, and target composition of molten steel are stable, the values are determined in advance through experiments and the like. The oxygen consumption rate during refining may be predicted using the expected time-dependent change pattern of the decarburization rate (ppm / min), and the oxygen supply rate (Nm 3 / h) may be controlled as described above. According to this method as well, it is possible to suppress excess oxygen with accuracy that does not cause any practical problem.
【００２０】精錬中のある時点での酸素消費速度を知る
ためには、その時の脱炭速度（ppm／min）が判ればよ
い。脱炭速度（ppm／min）は、例えば脱炭中に真空排気
中のガス成分を分析することによって求めることができ
る。その具体的方法は特開昭54−42324号公報に開示さ
れているところであるが、簡単に説明すると、例えば真
空排気中の排ガスをサンプリングし質量分析装置でＣＯ
2，Ｏ2，Ｎ2，Ａｒ，Ｈ2Ｏ，Ｈ2の各濃度を計測し、系
内（閉鎖容器内）に底吹き等により導入しているＡｒ流
量を基準に各ガス成分の排出流量を計算し、ＣＯおよび
ＣＯ2の排出流量から単位時間に系外に排出されるＣ量
を計算することによって脱炭速度（ppm／min）が求めら
れる。In order to know the oxygen consumption rate at a certain point during refining, the decarburization rate (ppm / min) at that time may be known. The decarburization rate (ppm / min) can be determined, for example, by analyzing the gas components in the vacuum exhaust during decarburization. The specific method is disclosed in Japanese Patent Application Laid-Open No. 54-42324.But briefly, for example, exhaust gas in vacuum exhaust is sampled, and CO is sampled by a mass spectrometer.
2 , O 2 , N 2 , Ar, H 2 O, and H 2 are measured, and the discharge flow rate of each gas component is determined based on the flow rate of Ar introduced into the system (closed vessel) by bottom blowing or the like. Is calculated, and the decarburization rate (ppm / min) is obtained by calculating the amount of C discharged outside the system per unit time from the discharge flow rates of CO and CO 2 .
【００２１】また、脱炭精錬中のある時点で設定すべき
目標酸素供給速度Ｑ（Nm3／h）は、脱炭速度Ｓ（ppm／m
in）と溶鋼質量Ｗ（kg）の値を、次式、 Ｑ＝ｎ×Ｓ×Ｗ×10-6×(22.4／24)×60 ・・（２） に代入することによって、直ちに求めることができる。
（２）式は、基本的には前記（１）式の脱炭反応に基づ
く酸素消費速度を算出するものであり、ｎ以外の各定数
は単位を換算するためのものである。ｎは本発明におい
て「酸素供給速度指数」と呼ぶ定数であり、その値は１
未満であることが特徴である。ｎ＝１のとき、Ｑは脱炭
速度Ｓ（ppm／min）に対応する酸素消費速度（Nm3／h）
に等しい。本発明の酸素供給速度コントロールは、前述
のように脱炭速度（酸素消費速度）が低下しつつある時
期に酸素供給が過剰にならないようにすることに重点を
置くものである。酸素供給速度指数ｎを１未満の定数と
すれば、脱炭速度の低下に追随した理想的な酸素供給速
度が算出できる。ｎの値を小さく設定するほど、過剰酸
素は安定して低減できる。ただしｎの値をあまり小さく
しすぎると、そのときの目標酸素供給速度Ｑ（Nm3／h）
では逆に酸素供給が脱炭反応に追いつかない状況にな
り、脱炭速度自体が低下して精錬時間の延長を招く。通
常のＶＯＤ精錬においては、（２）式におけるｎの値を
0.5程度まで小さくしても、初期［％Ｃ］値を従来より
低くできる効果と相まって精錬時間の延長をきたすこと
なく高い脱窒率（後述）を安定して実現することができ
る。特に、ｎの値を0.8以上0.95以下の範囲に設定すれ
ば、脱炭速度の低下が最も大きい時期においても約１分
間隔という実用的なデータ・サンプリング間隔によっ
て、過剰酸素は十分に低減され、かつ、脱炭反応速度の
低下もほとんど生じない。The target oxygen supply rate Q (Nm 3 / h) to be set at a certain point during the decarburization refining is determined by the decarburization rate S (ppm / m
in) and the mass of the molten steel W (kg) can be immediately obtained by substituting into the following equation: Q = n × S × W × 10 −6 × (22.4 / 24) × 60 (2) it can.
Equation (2) is basically for calculating the oxygen consumption rate based on the decarburization reaction of equation (1), and each constant other than n is for converting units. n is a constant called “oxygen supply rate index” in the present invention, and its value is 1
It is a feature that it is less than. When n = 1, Q is the oxygen consumption rate (Nm 3 / h) corresponding to the decarburization rate S (ppm / min)
be equivalent to. The oxygen supply rate control of the present invention focuses on preventing the oxygen supply from becoming excessive during the period when the decarburization rate (oxygen consumption rate) is decreasing as described above. If the oxygen supply rate index n is a constant less than 1, an ideal oxygen supply rate that follows a decrease in the decarburization rate can be calculated. Excess oxygen can be reduced more stably as the value of n is set smaller. However, if the value of n is too small, the target oxygen supply rate Q at that time (Nm 3 / h)
Then, on the contrary, the oxygen supply cannot keep up with the decarburization reaction, and the decarburization rate itself is reduced, which results in prolonging the refining time. In ordinary VOD refining, the value of n in equation (2) is
Even if it is reduced to about 0.5, a high denitrification rate (described later) can be stably realized without prolonging the refining time, in combination with the effect that the initial [% C] value can be made lower than before. In particular, if the value of n is set in the range of 0.8 or more and 0.95 or less, excess oxygen is sufficiently reduced by a practical data sampling interval of about 1 minute even at the time when the decarburization rate is the largest, In addition, the decarburization reaction rate hardly decreases.
【００２２】（２）式における酸素供給速度指数ｎは、
精錬中、常に同じ値に固定しておくことによって酸素供
給速度の算出が容易になる。データ・サンプリング間隔
等の操業条件に応じて最適な値に定数ｎを設定しておく
限りにおいて、終始失敗なくコントロールを続けること
が可能である。しかし、より一層高い精度で脱炭速度の
変化に追随させることを望むならば、脱炭速度の変化率
に応じてｎの値を規定範囲内で変動させてもよい。例え
ば、脱炭速度の変化が小さい時期にはｎを大き目の値
に、脱炭速度の変化が大きい時期にはｎを小さ目の値に
設定するのが好ましい。The oxygen supply rate index n in the equation (2) is
By constantly fixing the same value during refining, it becomes easy to calculate the oxygen supply rate. As long as the constant n is set to an optimum value in accordance with the operating conditions such as the data sampling interval, the control can be continued without any failure. However, if it is desired to follow the change in the decarburization speed with higher accuracy, the value of n may be varied within a specified range according to the rate of change in the decarburization speed. For example, it is preferable to set n to a large value when the change in the decarburization rate is small, and to set n to a small value when the change in the decarburization rate is large.
【００２３】図２は、酸素供給速度の設定パターンの違
いを、本発明の一例と従来例とで定性的に比較して示し
たものである。これは、脱炭速度の経時変化パターンが
いずれも結果的に同じになった場合の概念図であり、本
発明の例は脱炭中に数回、その時点での脱炭速度Ｓ（pp
m／min）を求め、ｎ＝0.9の前記（２）式によって算出
された目標酸素供給速度Ｑ（Nm3／h）に酸素供給速度を
その都度再設定した場合を想定したものである。一方、
従来例は脱炭中に脱炭速度の測定や酸素消費速度の算出
を実施せずに低窒素含クロム鋼を溶製する場合の一般的
な酸素供給パターンを想定したものである。本発明例の
方が従来例よりも酸素供給速度（Nm3／h）のパターンが
脱炭速度（ppm／min）のパターンに近づいており、酸素
の供給・消費のバランスが良いことがわかる。FIG. 2 shows a qualitative comparison between an example of the present invention and a conventional example of the difference in the setting pattern of the oxygen supply rate. This is a conceptual diagram in the case where the time-dependent change patterns of the decarburization rate are all the same as a result. In the example of the present invention, several times during the decarburization, the decarburization rate S (pp
m / min) and the oxygen supply rate is reset to the target oxygen supply rate Q (Nm 3 / h) calculated by the above equation (2) where n = 0.9. on the other hand,
The conventional example assumes a general oxygen supply pattern in the case of melting a low nitrogen chromium-containing steel without measuring the decarburization rate or calculating the oxygen consumption rate during decarburization. In the example of the present invention, the pattern of the oxygen supply rate (Nm 3 / h) is closer to the pattern of the decarburization rate (ppm / min) than the conventional example, and it can be seen that the balance of the supply and consumption of oxygen is better.
【００２４】ＶＯＤ処理に供する溶鋼には「未脱酸溶
鋼」と「脱酸溶鋼」があるが、例えば「未脱酸溶鋼」の
場合、真空引きを開始したのち閉鎖容器内の圧力が300T
orr前後になった時点から脱炭速度が大きくなり始め
る。この段階では脱炭反応に必要な酸素は溶鋼中からも
賄われる。「脱酸溶鋼」であっても真空排気前あるいは
真空排気開始後に過剰となり過ぎない所定量の酸素を溶
鋼に供給したのち真空排気を継続することによって同等
の状況が得られる。したがって、脱炭速度が最大になる
前に「酸素供給速度＜酸素消費速度」となるコントロー
ルを開始することが、過剰酸素を抑制するうえで望まし
い。閉鎖容器内の圧力が300Torr前後まで低下しないと
脱炭はほとんど進行しないため、真空排気開始後に閉鎖
容器内の圧力が300Torr以下になってから上記コントロ
ールを開始するのがよい。The molten steel to be subjected to the VOD treatment includes "non-deoxidized molten steel" and "deoxidized molten steel". For example, in the case of "non-deoxidized molten steel", the pressure in the closed vessel is 300 T after evacuation is started.
The decarburization speed starts to increase from around the time of orr. At this stage, the oxygen required for the decarburization reaction is also supplied from the molten steel. Even in the case of "deoxidized molten steel", the same situation can be obtained by supplying a predetermined amount of oxygen to the molten steel before the evacuation or after starting the evacuation, and then continuing the evacuation. Therefore, it is desirable to start the control for satisfying “oxygen supply rate <oxygen consumption rate” before the decarburization rate becomes maximum in order to suppress excess oxygen. Since decarburization hardly progresses unless the pressure in the closed vessel is reduced to around 300 Torr, it is preferable to start the above control after the pressure in the closed vessel becomes 300 Torr or less after starting the evacuation.
【００２５】また、溶鋼中の炭素濃度［％Ｃ］が約0.15
質量％に低下するまでは脱窒反応の進行が期待できるた
め、上記酸素供給速度コントロールは［％Ｃ］が0.15質
量％以下に低下したのち終了することが望ましい。The carbon concentration [% C] in the molten steel is about 0.15
Since the progress of the denitrification reaction can be expected until the amount decreases to mass%, the oxygen supply rate control is desirably terminated after [% C] has decreased to 0.15% by mass or less.
【００２６】本発明の脱窒方法は、Ｃｒ含有量が概ね11
〜30質量％の範囲のステンレス鋼に適用でき、特に窒素
含有量が0.01質量％以下の低窒素鋼を製造するのに適し
ている。本発明の脱窒処理に共する鋼の［％Ｃ］は少な
くとも0.15質量％以上としておく必要があるが、あまり
高くする必要はない。脱窒促進と精錬時間の遅延防止の
観点から脱窒処理前の［％Ｃ］は0.25〜0.5質量％の範
囲としておくことが望ましい。The denitrification method of the present invention has a Cr content of about 11
It can be applied to stainless steel in the range of up to 30% by mass, and is particularly suitable for producing low-nitrogen steel having a nitrogen content of 0.01% by mass or less. [% C] of the steel used in the denitrification treatment of the present invention must be at least 0.15% by mass or more, but does not need to be too high. [% C] before the denitrification treatment is desirably in the range of 0.25 to 0.5% by mass from the viewpoints of promoting denitrification and preventing delay of the refining time.
【００２７】[0027]
【実施例】ＳＵＳ４４４系の溶鋼を用いてＶＯＤで脱窒
実験を行った。溶製工程は電気炉−転炉−ＶＯＤとし、
転炉での粗脱炭終了後の溶鋼は未脱酸で出鋼した。１チ
ャージは約70トンである。EXAMPLE A denitrification experiment was conducted by VOD using SUS444 type molten steel. Melting process is electric furnace-converter-VOD,
The molten steel after the completion of the crude decarburization in the converter was discharged without deoxidation. One charge is about 70 tons.
【００２８】図３に、使用したＶＯＤ設備の概略を示
す。この設備は、転炉から出鋼した溶鋼２が入った取鍋
３を真空容器４内へセットし、真空容器カバー５で真空
容器４を密閉し、真空容器４と真空容器カバー５によっ
て形成された閉鎖容器内のガスを真空排気管１４から抜
き取ることにより該閉鎖容器内を減圧状態にし、該減圧
下で酸素供給パイプ１５から溶鋼に酸素を吹き付けて溶
鋼２中の炭素を脱炭するものである。酸素供給パイプ１
５に導入される酸素量は酸素流量計１６によって計測さ
れ、酸素流量制御弁１７によって酸素供給速度を変える
ことができるようになっている。真空排気管１４は真空
排気装置１０につながっており、真空排気管１４の途中
には真空計１１，質量分析装置１２，排ガス流量計１３
が備わっている。質量分析装置１２は排ガスをサンプリ
ングして排ガス中の各ガス成分の濃度が測定できるよう
になっている。取鍋３の底部に設けられた底吹きガス供
給口７が真空容器４内に設置された底吹きガス供給管１
９に接続され、底吹きガス供給口７から溶鋼２中にＡｒ
ガスが導入できるようになっている。FIG. 3 shows an outline of the VOD equipment used. In this equipment, a ladle 3 containing molten steel 2 discharged from a converter is set in a vacuum vessel 4, the vacuum vessel 4 is closed with a vacuum vessel cover 5, and the vacuum vessel 4 and the vacuum vessel cover 5 are formed. The inside of the closed vessel is decompressed by extracting the gas in the closed vessel from the vacuum exhaust pipe 14, and oxygen is blown from the oxygen supply pipe 15 to the molten steel under the reduced pressure to decarbonize the carbon in the molten steel 2. is there. Oxygen supply pipe 1
The amount of oxygen introduced into 5 is measured by an oxygen flow meter 16, and the oxygen supply speed can be changed by an oxygen flow control valve 17. The vacuum exhaust pipe 14 is connected to the vacuum exhaust device 10, and a vacuum gauge 11, a mass spectrometer 12, and an exhaust gas flow meter 13 are provided in the middle of the vacuum exhaust pipe 14.
Is provided. The mass spectrometer 12 can sample the exhaust gas and measure the concentration of each gas component in the exhaust gas. The bottom blown gas supply port 7 provided at the bottom of the ladle 3 is connected to the bottom blown gas supply pipe 1 installed in the vacuum vessel 4.
9 from the bottom blown gas supply port 7 into the molten steel 2.
Gas can be introduced.
【００２９】〔本発明例〕真空処理前（転炉出鋼後）の
［％Ｃ］値が約0.25〜0.5質量％の範囲にあるＳＵＳ４
４４系溶鋼について、真空排気開始後に真空計１１の測
定値が300Torrを下回った時点で真空排気ガスの最初の
サンプリングを行い、質量分析装置１２によってＣ
Ｏ2，Ｏ2，Ｎ2，Ａｒ，Ｈ2Ｏ，Ｈ2の各濃度を測定し
た。この測定値およびサンプリング時の底吹きＡｒ流量
値を計算制御装置に入力し、酸素流量制御弁１７の開度
をフィードバック制御した。その際、計算制御装置にお
いては、入力データから各ガス成分の排出流量を計算
し、ＣＯおよびＣＯ2の排出流量から単位時間に排出さ
れるＣ量を計算することによって脱炭速度（ppm／min）
を算出し、この脱炭速度と溶鋼質量を前記（２）式に代
入して目標酸素供給速度（Nm3／h）を求めた。（２）式
における酸素供給速度指数ｎの値は0.6〜0.95の範囲の
定数（チャージにより異なる）とした。酸素供給パイプ
１５からの酸素供給速度が目標酸素供給速度（Nm3／h）
と等しくなるよう酸素流量制御弁１７の開度をフィード
バック制御した。その後、１〜５分間隔で繰り返しガス
サンプリングを行い、各サンプリング毎に同様の手法で
酸素供給速度の域値を再設定し、酸素流量制御弁１７の
開度をフィードバック制御することによって酸素供給速
度のコントロールを行った。真空排気ガスの分析に基づ
いて求めた溶鋼中の炭素濃度［％Ｃ］が0.15質量％以下
になった時点で酸素供給速度のコントロールを終了し、
その後はそのまま一定の酸素供給速度で目標［％Ｃ］に
なるまで脱炭を続けた。なお、（２）式における酸素供
給速度指数ｎの値はコントロール開始から終了まで同じ
値に固定した。[Example of the present invention] SUS4 having a [% C] value before the vacuum treatment (after tapping from the converter) in the range of about 0.25 to 0.5% by mass.
When the measured value of the vacuum gauge 11 falls below 300 Torr after the start of evacuation of the 44 series molten steel, the first sampling of the evacuation gas is performed, and
The concentrations of O 2 , O 2 , N 2 , Ar, H 2 O, and H 2 were measured. The measured value and the flow rate of the bottom blown Ar at the time of sampling were input to the calculation control device, and the opening of the oxygen flow control valve 17 was feedback-controlled. At this time, the calculation control device calculates the discharge flow rate of each gas component from the input data, and calculates the amount of C discharged per unit time from the discharge flow rates of CO and CO 2 , thereby decarbonizing the carbon dioxide (ppm / min). )
The target oxygen supply rate (Nm 3 / h) was determined by substituting the decarburization rate and the mass of the molten steel into the above equation (2). The value of the oxygen supply rate index n in the equation (2) was a constant in the range of 0.6 to 0.95 (depending on the charge). The oxygen supply rate from the oxygen supply pipe 15 is the target oxygen supply rate (Nm 3 / h)
The opening degree of the oxygen flow control valve 17 was feedback-controlled so as to be equal to Thereafter, gas sampling is repeatedly performed at intervals of 1 to 5 minutes, the threshold value of the oxygen supply speed is reset by the same method for each sampling, and the opening of the oxygen flow rate control valve 17 is feedback-controlled to perform the oxygen supply speed. Was performed. When the carbon concentration [% C] in the molten steel obtained based on the analysis of the vacuum exhaust gas becomes 0.15% by mass or less, the control of the oxygen supply rate is terminated,
Thereafter, decarburization was continued at a constant oxygen supply rate until the target [% C] was reached. The value of the oxygen supply rate index n in the equation (2) was fixed at the same value from the start to the end of the control.
【００３０】ガスサンプリングの間隔は脱炭速度の変化
率に応じて１〜５分の間で変化させた。例えば、真空処
理前の［％Ｃ］が0.4質量％であった１チャージの例を
示すと、酸素供給速度のコントロールを開始してから脱
炭速度がほぼ定常状態になるまで１分間隔で５回、その
後３分間隔で６回、脱炭速度が低下し始めてからは２分
間隔で５回の、合計１６回のガスサンプリングを行っ
た。なお、このチャージにおいては（２）式の酸素供給
速度指数ｎを0.9とした。The gas sampling interval was varied between 1 and 5 minutes according to the rate of change of the decarburization rate. For example, as an example of one charge in which [% C] before vacuum treatment was 0.4% by mass, 5 minutes at one minute intervals from the start of control of the oxygen supply rate until the decarburization rate became almost steady. Gas sampling was performed six times at three-minute intervals, and five times at two-minute intervals after the decarburization rate began to decrease, a total of 16 times. In this charge, the oxygen supply rate index n in equation (2) was set to 0.9.
【００３１】各チャージについて、真空処理後（脱炭
後）の溶鋼サンプルを採取し、鋼中の窒素濃度［％Ｎ］
（質量％）を分析し、次式で定義される「脱窒率」で脱
窒効果を評価した。 脱窒率＝（真空処理前［％Ｎ］−真空処理後［％Ｎ］）
／真空処理前［％Ｎ］×100For each charge, a molten steel sample after vacuum treatment (after decarburization) was collected, and the nitrogen concentration in the steel [% N]
(Mass%) was analyzed, and the denitrification effect was evaluated based on the “denitrification rate” defined by the following equation. Denitrification rate = (Before vacuum treatment [% N]-After vacuum treatment [% N])
/ Before vacuum treatment [% N] × 100
【００３２】〔比較例〕真空処理前（転炉出鋼後）の
［％Ｃ］値が約0.15〜0.6質量％の範囲にあるＳＵＳ４
４４系溶鋼について、酸素供給速度が酸素消費速度より
小さくなるようにするコントロールを行わない従来法で
ＶＯＤでの脱炭・脱窒を試みた。脱炭中の酸素供給速度
は先の図２に示した従来例のパターンのように３段階に
変化させた。例えば、真空処理前の［％Ｃ］が約0.5質
量％であった１チャージの例を示すと、酸素吹精開始か
ら２０分経過時点、および３０分経過時点で酸素供給速
度を変化させた。このとき、各段階での酸素供給速度指
数は各々1.7、1.4、1.2であった。各チャージについ
て、上記発明例の場合と同様に「脱窒率」で脱窒効果を
評価した。[Comparative Example] SUS4 having a [% C] value before the vacuum treatment (after tapping from the converter) in the range of about 0.15 to 0.6% by mass.
Regarding the 44 type molten steel, decarburization and denitrification by VOD were attempted by a conventional method without controlling the oxygen supply rate to be lower than the oxygen consumption rate. The oxygen supply rate during the decarburization was changed in three stages as in the pattern of the conventional example shown in FIG. For example, in the case of one charge in which [% C] before the vacuum treatment was about 0.5% by mass, the oxygen supply rate was changed at a lapse of 20 minutes and at a lapse of 30 minutes from the start of oxygen blowing. At this time, the oxygen supply rate index at each stage was 1.7, 1.4, and 1.2, respectively. For each charge, the denitrification effect was evaluated in terms of the "denitrification rate" in the same manner as in the case of the above-mentioned invention example.
【００３３】以上の本発明例と比較例の評価結果を図４
に示す。真空処理前［％Ｃ］が同等のもので比較した場
合、本発明例では従来例よりも高い脱窒率が得られてい
る。また、同等の脱窒率を得るのに、本発明例では従来
例よりも低い真空処理前［％Ｃ］とすることができ、脱
炭時間の短縮化が図られた。さらに、本発明例では従来
例よりも真空処理前［％Ｃ］に対する脱窒率のバラツキ
が小さくなっている。すなわち、本発明法に従えばＶＯ
Ｄ処理において従来よりも高位安定した脱窒率が得られ
ることが確認された。FIG. 4 shows the evaluation results of the present invention example and the comparative example.
Shown in When compared with those before [% C] before the vacuum treatment, a higher denitrification rate was obtained in the example of the present invention than in the conventional example. Further, in order to obtain the same denitrification rate, in the example of the present invention, it is possible to set the pre-vacuum treatment [% C] lower than that of the conventional example, thereby shortening the decarburization time. Further, in the example of the present invention, the variation in the denitrification rate with respect to the [% C] before the vacuum treatment is smaller than in the conventional example. That is, according to the method of the present invention, VO
It was confirmed that a higher and more stable denitrification rate was obtained in the D treatment than before.
【００３４】[0034]
【発明の効果】以上のように、本発明では酸素供給速度
をコントロールすることによってクロム含有鋼の脱窒を
効率的に短時間で行う方法を開示した。この方法は特に
ＶＯＤにおいて低炭素域での脱窒効率を高めるので、低
窒素含クロム鋼を短時間で溶製するのに適している。し
かも、既存の製鋼設備を利用して比較的簡単に実施でき
るため、低窒素含クロム鋼の製造コスト低減につなが
り、その普及に寄与するものである。As described above, the present invention has disclosed a method for efficiently denitrifying chromium-containing steel in a short time by controlling the oxygen supply rate. This method is particularly suitable for smelting low-nitrogen chromium-containing steel in a short time because the method improves the denitrification efficiency in the low carbon region especially in VOD. Moreover, since it can be carried out relatively easily using existing steelmaking equipment, it leads to a reduction in the production cost of low nitrogen chromium-containing steel and contributes to its widespread use.
【図１】ＶＯＤにおいて十分に酸素を供給したときの溶
鋼中炭素濃度および脱炭速度の一般的な経時変化を定性
的に表したグラフ。FIG. 1 is a graph qualitatively showing general time-dependent changes in carbon concentration and decarburization rate in molten steel when oxygen is sufficiently supplied in VOD.
【図２】ＶＯＤにおける脱炭速度の経時変化パターンお
よびそのパターンに対応する本発明の一例と従来例での
酸素供給速度の設定パターンを定性的に表したグラフ。FIG. 2 is a graph qualitatively showing a time-dependent change pattern of a decarburization rate in VOD and a setting pattern of an oxygen supply rate in one example of the present invention and a conventional example corresponding to the pattern.
【図３】実施例において使用したＶＯＤ設備の構成を表
す概略図。FIG. 3 is a schematic diagram showing a configuration of a VOD facility used in the embodiment.
【図４】ＶＯＤ処理における真空処理前［％Ｃ］と脱窒
率の関係を表すグラフ。FIG. 4 is a graph showing a relationship between [% C] before vacuum processing and a denitrification rate in VOD processing.
【符号の説明】 １ ＶＯＤ設備 ２ 溶鋼 ３ 取鍋 ４ 真空容器４内へセットし、 ５ 真空容器カバー ６ 中蓋 ７ 底吹きガス供給口 ８ 測温プローブ ９ 副原料添加装置 １０ 真空排気装置 １１ 真空計 １２ 質量分析装置 １３ 排ガス流量計 １４ 真空排気管 １５ 酸素供給パイプ １６ 酸素流量計 １７ 酸素流量制御弁 １８ 酸素タンク １９ 底吹きガス供給管[Description of Signs] 1 VOD equipment 2 Molten steel 3 Ladle 4 Set in vacuum container 4, 5 Vacuum container cover 6 Inner lid 7 Bottom blown gas supply port 8 Temperature measuring probe 9 Secondary material addition device 10 Vacuum exhaust device 11 Vacuum Total 12 Mass spectrometer 13 Exhaust gas flow meter 14 Vacuum exhaust pipe 15 Oxygen supply pipe 16 Oxygen flow meter 17 Oxygen flow control valve 18 Oxygen tank 19 Bottom blown gas supply pipe
Claims (7)
き付けて脱炭を行う含クロム溶鋼の精錬において脱炭反
応のボイリングを利用して該溶鋼の脱窒を行うに際し、
酸素供給速度（Nm3／h）を、下記（１）式の脱炭反応に
おける酸素消費速度（Nm3／h）より小さくなるようにコ
ントロールしながら酸素を吹き付ける、含クロム溶鋼の
脱窒方法。 ２Ｃ＋Ｏ2→２ＣＯ ・・（１）In the refining of chromium-containing molten steel, which is degassed by blowing oxygen while evacuating in a closed vessel, the denitrification of the molten steel is performed by utilizing the boiling of the decarburization reaction.
A method for denitrifying chromium-containing molten steel, in which oxygen is blown while controlling the oxygen supply rate (Nm 3 / h) to be smaller than the oxygen consumption rate (Nm 3 / h) in the decarburization reaction of the following formula (1). 2C + O 2 → 2CO ・ ・ (1)
度（Nm3／h）は、予め定めてある脱炭速度（ppm／min）
の予想経時変化パターンを用いて算出したものである、
請求項１に記載の含クロム溶鋼の脱窒方法。2. The oxygen consumption rate (Nm 3 / h) in the decarburization reaction of the formula (1) is a predetermined decarburization rate (ppm / min).
It is calculated using the expected temporal change pattern of
The method for denitrifying chromium-containing molten steel according to claim 1.
度（Nm3／h）は、当該脱炭中に真空排気中のガス成分を
分析して求めた脱炭速度（ppm／min）に基づいて算出し
たものである、請求項１に記載の含クロム溶鋼の脱窒方
法。3. The oxygen consumption rate (Nm 3 / h) in the decarburization reaction of the formula (1) is determined by analyzing a gas component in vacuum exhaust during the decarburization (ppm / min). The method for denitrifying chromium-containing molten steel according to claim 1, wherein the method is calculated on the basis of:
き付けて脱炭を行う含クロム溶鋼の精錬において脱炭反
応のボイリングを利用して該溶鋼の脱窒を行うに際し、
脱炭中に、下記（２）式を用いて目標酸素供給速度Ｑ
（Nm3／h）を連続的にまたは繰り返し算出し、酸素供給
速度（Nm3／h）を該目標酸素供給速度Ｑになるようにコ
ントロールしながら酸素を吹き付ける、含クロム溶鋼の
脱窒方法。 Ｑ＝ｎ×Ｓ×Ｗ×10-6×(22.4／24)×60 ・・（２） ただし、ｎは酸素供給速度指数であって0.5以上１未満
の範囲にある定数、Ｓは脱炭速度（ppm／min）を表す変
数、Ｗは溶鋼質量（kg）を表す定数である。4. In the refining of chromium-containing molten steel in which oxygen is blown while evacuating in a closed vessel to decarburize the chromium-containing molten steel, the denitrification of the molten steel is performed by utilizing the boiling of the decarburization reaction.
During decarburization, the target oxygen supply rate Q is calculated using the following equation (2).
(Nm 3 / h) is continuously or repeatedly calculated, and oxygen is blown while controlling the oxygen supply rate (Nm 3 / h) to the target oxygen supply rate Q, thereby denitrifying chromium-containing molten steel. Q = n × S × W × 10 −6 × (22.4 / 24) × 60 (2) where n is an oxygen supply rate index and is a constant in the range of 0.5 or more and less than 1, and S is a decarburization rate. (Ppm / min), and W is a constant representing the mass (kg) of molten steel.
炭中に真空排気中のガス成分を分析して求めたものであ
る、請求項４に記載の含クロム溶鋼の脱窒方法。5. The method for denitrifying chromium-containing molten steel according to claim 4, wherein the decarburization rate S in the equation (2) is obtained by analyzing a gas component in a vacuum exhaust during the decarburization. .
0.8以上0.95以下の範囲にある定数である、請求項４ま
たは５に記載の含クロム溶鋼の脱窒方法。6. The oxygen supply rate index n in equation (2) is
The method for denitrifying chromium-containing molten steel according to claim 4 or 5, wherein the constant is a constant in the range of 0.8 to 0.95.
気開始後に閉鎖容器内の圧力が300Torr以下になってか
ら開始し、溶鋼中の炭素濃度が0.15質量％以下に低下し
てから終了する、請求項４，５または６に記載の含クロ
ム溶鋼の脱窒方法。7. The control of the oxygen supply rate is started when the pressure in the closed vessel becomes 300 Torr or less after the start of evacuation, and is ended after the carbon concentration in the molten steel falls to 0.15 mass% or less. Item 7. The method for denitrifying chromium-containing molten steel according to item 4, 5 or 6.
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|---|---|---|---|
| JP04634298A JP3827852B2 (en) | 1998-02-13 | 1998-02-13 | Denitrification method for chromium-containing molten steel |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP04634298A JP3827852B2 (en) | 1998-02-13 | 1998-02-13 | Denitrification method for chromium-containing molten steel |
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| JP3827852B2 JP3827852B2 (en) | 2006-09-27 |
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|---|---|---|---|---|
| JP2016069670A (en) * | 2014-09-29 | 2016-05-09 | 新日鐵住金株式会社 | Method for producing alloy |
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Cited By (1)
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|---|---|---|---|---|
| JP2016069670A (en) * | 2014-09-29 | 2016-05-09 | 新日鐵住金株式会社 | Method for producing alloy |
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