JP3412924B2 - Refining method of chromium-containing molten steel - Google Patents
Refining method of chromium-containing molten steelInfo
- Publication number
- JP3412924B2 JP3412924B2 JP22538094A JP22538094A JP3412924B2 JP 3412924 B2 JP3412924 B2 JP 3412924B2 JP 22538094 A JP22538094 A JP 22538094A JP 22538094 A JP22538094 A JP 22538094A JP 3412924 B2 JP3412924 B2 JP 3412924B2
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- gas
- concentration
- refining
- molten steel
- vacuum
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Description
【0001】[0001]
【産業上の利用分野】本発明は含クロム溶鋼の脱炭処理
後の還元処理において、高価なArガスの使用量を抑
え、かつ[N]濃度の制御を効率的に行う含クロム溶鋼
の精錬法に関する。BACKGROUND OF THE INVENTION The present invention relates to refining of molten chromium-containing steel for reducing the amount of expensive Ar gas and efficiently controlling the [N] concentration in the reduction treatment after decarburization of molten chromium-containing steel. Concerning the law.
【0002】[0002]
【従来の技術】従来、ステンレス鋼のごとき11mas
s%以上のクロムを含むような含クロム溶鋼の精錬法と
しては、浴面下より酸素ガスまたは酸素ガス(以下、単
に酸素という)と不活性ガスの混合ガスを吹込むAOD
法が広く用いられている。AOD法は脱炭が進行し、溶
鋼中の[C]濃度が低下してくると[Cr]が酸化され
やすくなることから、[C]濃度の低下に伴い吹込みガ
ス中のArガスやN2 ガスのような不活性ガスの比率を
高くし、酸素の比率を低くして[Cr]の酸化を抑える
方法がとられている。しかし、該方法でも[Cr]の酸
化が進行するため、目標[C]濃度まで脱炭した後に、
酸化した[Cr]を回収するために不活性ガスのみを吹
込みながら、SiやAl等の還元剤を添加して処理する
還元処理を行っている。2. Description of the Related Art Conventionally, 11mas such as stainless steel
As a refining method for molten chromium-containing steel containing s% or more of chromium, AOD in which oxygen gas or a mixed gas of oxygen gas (hereinafter simply referred to as oxygen) and an inert gas is blown from below the bath surface
The method is widely used. In the AOD method, when decarburization progresses and [C] concentration in molten steel decreases, [Cr] is easily oxidized. Therefore, as the [C] concentration decreases, Ar gas and N in the blown gas are reduced. A method of suppressing the oxidation of [Cr] by increasing the ratio of an inert gas such as 2 gas and decreasing the ratio of oxygen is adopted. However, since the oxidation of [Cr] proceeds even in this method, after decarburization to the target [C] concentration,
In order to recover the oxidized [Cr], a reducing treatment is performed by adding a reducing agent such as Si or Al while blowing only an inert gas.
【0003】含クロム溶鋼は、多量に含まれる[Cr]
が溶鋼中の[N]の活量を大幅に低下させるため、
[N]の溶解度が大きく、不活性ガスとしてN2 ガスの
みを吹込んだ場合には[N]濃度は0.2mass%以
上にもなる。特殊な鋼種を除き、一般的な製品に要求さ
れる[N]濃度は0.1mass%以下であり、このた
めAOD法では脱炭の初期を除き、不活性ガスとして高
価なArガスを使用する必要があり、経済的に不利にな
っていた。Chromium-containing molten steel is contained in a large amount [Cr].
Significantly reduces the activity of [N] in molten steel,
The solubility of [N] is high, and when only N 2 gas is blown as the inert gas, the [N] concentration becomes 0.2 mass% or more. Except for special steel grades, the [N] concentration required for general products is 0.1 mass% or less. Therefore, in the AOD method, expensive Ar gas is used as the inert gas except for the initial stage of decarburization. Needed and was at a financial disadvantage.
【0004】このような問題点を解決する方法として、
特開平4−21486号公報および特開平4−2630
05号公報記載の方法が提案されている。これらの含ク
ロム溶鋼の精錬方法は、同一精錬容器を用いて、[C]
濃度0.2〜0.05mass%までは吹込みガスとし
てN2 ガスを主体とした非酸化性ガスと酸素の混合ガス
を使用し、[C]濃度がこの範囲内に低下した後は、2
00〜15Torrに減圧し、かつ吹込みガスとしてN
2 ガスを主体とした非酸化性ガスのみを使用して目標
[C]濃度までの脱炭を行い、その後、吹込みガスをA
rガスとして、酸化した[Cr]を回収するために還元
剤を添加して処理する方法である。これらの方法によ
り、脱炭処理ではArガスを使用する必要はなくなる
が、還元処理ではArガスの使用が必須である。また、
これらの方法では、還元処理時の真空度およびArガス
の吹込み時間が規定されていないため、還元処理後の
[N]濃度にばらつきを生じ、効率的な精錬とは言えな
い。As a method of solving such a problem,
JP-A-4-21486 and JP-A-4-2630
The method described in Japanese Patent Publication No. 05 has been proposed. The refining method for these molten chromium-containing steels uses the same refining vessel [C].
A mixed gas of a non-oxidizing gas mainly composed of N 2 gas and oxygen is used as a blowing gas up to a concentration of 0.2 to 0.05 mass%, and after the [C] concentration falls within this range, 2
The pressure is reduced to 00 to 15 Torr, and N is used as a blowing gas.
Decarburization to the target [C] concentration is performed using only non-oxidizing gas consisting mainly of 2 gases, and then the injected gas is A
This is a method in which a reducing agent is added and treated in order to recover oxidized [Cr] as r gas. By these methods, it is not necessary to use Ar gas in the decarburization treatment, but it is essential to use Ar gas in the reduction treatment. Also,
In these methods, since the degree of vacuum and the blowing time of Ar gas during the reduction treatment are not specified, the [N] concentration after the reduction treatment varies, and it cannot be said that the refining is efficient.
【0005】[0005]
【発明が解決しようとする課題】本発明は、同一精錬容
器を用いて大気圧精錬後、真空精錬を用いる含クロム溶
鋼の精錬法において、還元処理時の真空度を目標[N]
濃度に応じて制御することにより、還元処理時に高価な
Arガスに換えて安価なN2 ガスの使用を可能とし、か
つ容易に[N]濃度の制御を可能とする効率的な精錬法
を提供することを目的とするものである。DISCLOSURE OF THE INVENTION The present invention aims at the degree of vacuum during reduction treatment in a refining method for molten chromium-containing steel using vacuum refining after atmospheric refining using the same refining vessel [N].
Providing an efficient refining method that makes it possible to use inexpensive N 2 gas instead of expensive Ar gas during the reduction process and to easily control the [N] concentration by controlling according to the concentration The purpose is to do.
【0006】[0006]
【課題を解決するための手段】本発明は、上述の課題を
有利に解決したものであり、その要旨とするところは下
記のとおりである。
(1)同一の精錬容器を用いて大気圧下での脱炭処理
後、真空下での脱炭および還元処理を行う含クロム溶鋼
の精錬法において、前記還元処理の吹込みガスとして溶
鋼トン当り0.2Nm3 /min以上のN2 ガスを吹込
み、かつ目標[N]濃度に合わせて下記式および式
を満足する真空度で少くとも1min還元処理すること
を特徴とする含クロム溶鋼の精錬法。
a=−1.35−{3280/(T+273)−0.75}(0.01[Ni]−0.045[Cr]+0.009) …
P≦760([N]2×10-2a ) +10 ……
T :溶鋼温度(℃)
[Ni]:溶鋼中の[Ni]濃度(mass%)
[Cr]:溶鋼中の[Cr]濃度(mass%)
P :還元処理時の真空度(Torr)
[N] :目標[N]濃度(mass%)
(2)同一の精錬容器を用いて大気圧下での脱炭処理
後、真空下での脱炭および還元処理を行う含クロム溶鋼
の精錬法において、前記還元処理の吹込みガスとして溶
鋼トン当り0.2Nm3 /min以上のN2 ガスとAr
ガスの混合ガスを吹込み、かつ目標[N]濃度に合わせ
て下記式および式を満足する真空度で少くとも1m
in還元処理することを特徴とする含クロム溶鋼の精錬
法。
a=−1.35−{3280/(T+273)−0.75}(0.01[Ni]−0.045[Cr]+0.009) …
P≦760([N]2×10-2a ) {(QAr+QN2)/QAr}+10 ……
T :溶鋼温度(℃)
[Ni]:溶鋼中の[Ni]濃度(mass%)
[Cr]:溶鋼中の[Cr]濃度(mass%)
P :還元処理時の真空度(Torr)
[N] :目標[N]濃度(mass%)
QAr :Arガスの吹込み流量(Nm3 /min)
QN2 :N2 ガスの吹込み流量(Nm3 /min)
(3)同一の精錬容器を用いて大気圧下での脱炭処理
後、還元処理のみを真空下で行うことを特徴とする前項
(1)または(2)記載の含クロム溶鋼の精錬法。The present invention advantageously solves the above-mentioned problems, and the gist thereof is as follows. (1) In a refining method for molten chromium-containing steel, in which decarburization treatment under atmospheric pressure is performed using the same refining vessel, decarburization and reduction treatment under vacuum is performed, in molten steel per ton of molten gas as a blowing gas of the reduction treatment. Smelting of chromium-containing molten steel, characterized in that N 2 gas of 0.2 Nm 3 / min or more is blown, and reduction treatment is carried out in accordance with the target [N] concentration at a vacuum degree satisfying the following formula and formula for at least 1 min. Law. a = -1.35- {3280 / (T + 273) -0.75} (0.01 [Ni] -0.045 [Cr] +0.009) ... P ≤ 760 ([N] 2 x 10 -2a ) +10 ... T: Molten steel temperature (° C) [Ni]: [Ni] concentration in molten steel (mass%) [Cr]: [Cr] concentration in molten steel (mass%) P: Degree of vacuum during reduction treatment (Torr) [N]: Target [ N] concentration (mass%) (2) In the refining method for molten chromium-containing steel, which comprises decarburizing treatment under atmospheric pressure using the same refining vessel, decarburizing and reducing treatment under vacuum, As blowing gas, N 2 gas of 0.2 Nm 3 / min or more per ton of molten steel and Ar
A mixed gas of gas is blown, and the degree of vacuum satisfying the following formula and formula is adjusted to at least the target [N] concentration and at least 1 m.
A method for refining molten chromium-containing steel, characterized by performing a reduction treatment. a = -1.35- {3280 / (T + 273) -0.75} (0.01 [Ni] -0.045 [Cr] +0.009) ... P≤760 ([N] 2 × 10 -2a ) {(Q Ar + Q N2 ) / Q Ar } +10 ...... T: Molten steel temperature (° C) [Ni]: [Ni] concentration (mass%) in molten steel [Cr]: [Cr] concentration (mass%) in molten steel P: During reduction treatment Degree of vacuum (Torr) [N]: Target [N] concentration (mass%) Q Ar : Ar gas blowing flow rate (Nm 3 / min) Q N2 : N 2 gas blowing flow rate (Nm 3 / min) ( 3) The refining method for molten chromium-containing steel as described in the above item (1) or (2), which comprises performing decarburization treatment under atmospheric pressure using the same refining vessel and then performing only reduction treatment under vacuum.
【0007】以下に本発明について詳細に説明する。本
発明の含クロム溶鋼の精錬方法は、図1に例示するよう
な精錬方法である。精錬容器1内で含クロム溶鋼4中に
底吹き羽口2を通して精錬ガス5を吹込む。また、精錬
容器1は着脱可能な排気フード3を有しており、任意の
真空度までの減圧が可能である。本発明法の精錬では、
精錬のはじめは排気フード3のない状態で大気圧精錬を
行い、その後排気フード3を装着し、真空引きを開始し
て真空精錬を行う方法である。The present invention will be described in detail below. The refining method for molten chromium-containing steel of the present invention is a refining method as illustrated in FIG. The refining gas 5 is blown into the molten chromium-containing steel 4 in the refining vessel 1 through the bottom blowing tuyere 2. Further, the refining container 1 has a detachable exhaust hood 3 and can reduce the pressure to an arbitrary degree of vacuum. In the refining of the method of the present invention,
At the beginning of refining, atmospheric pressure refining is performed without the exhaust hood 3, then the exhaust hood 3 is attached, vacuuming is started, and vacuum refining is performed.
【0008】本発明は、溶鋼中の[O]濃度が低くなる
還元処理では脱窒速度が速いことに着目し、N2 ガスを
吹込む場合には真空度の調整、N2 ガスとArガスの混
合ガスを吹込む場合には真空度および吹込みガス中のN
2 ガスの比率を調整することにより、製品に要求される
目標[N]濃度に調整することを可能とするものであ
る。The present invention focuses on the fact that the denitrification rate is high in the reduction treatment in which the concentration of [O] in the molten steel becomes low. When N 2 gas is blown, the degree of vacuum is adjusted, N 2 gas and Ar gas are adjusted. Degree of vacuum and N in the blown gas when blowing the mixed gas of
By adjusting the ratio of the two gases, it is possible to adjust the target [N] concentration required for the product.
【0009】図2にSUS304ステンレス鋼を同一精
錬容器を用いて大気圧精錬後、真空精錬を実施した場合
の還元処理時の真空度と溶鋼中[N]濃度の関係を示
す。なお、吹込みガスとしてはN2 ガスのみを用いて、
真空度一定状態で溶鋼トン当り0.2Nm3 /min以
上で1min以上吹込んだ後の値であり、図中の○印が
実測値で、実線は実験的に求められた線である。図2よ
り[N]濃度は真空度の低下とともに低下することがわ
かる。例えば、[N]濃度を0.05mass%に調整
するには真空度を約40Torr以下にすればよい。図
中の実線は種々の鋼種、溶鋼温度および真空度の条件下
で求められた関係であるが、式で表すと下記式および
式となる。
a=−1.35−{3280/(T+273)−0.75}(0.01[Ni]−0.045[Cr]+0.009) …
P=760([N]2×10-2a ) ……
図2および式、式より、溶鋼温度、溶鋼中の[N
i]、[Cr]濃度に合わせて真空度を調整すれば、N
2 ガス単独吹込みでも任意の[N]濃度に制御できるこ
とが確認された。FIG. 2 shows the relationship between the vacuum degree and the [N] concentration in the molten steel during the reduction treatment when SUS304 stainless steel is subjected to atmospheric pressure refining using the same refining vessel and then vacuum refining. In addition, using only N 2 gas as the blowing gas,
It is a value after blowing for 1 min or more at 0.2 Nm 3 / min or more per ton of molten steel in a state where the degree of vacuum is constant. The circles in the figure are the measured values, and the solid line is the line obtained experimentally. It can be seen from FIG. 2 that the [N] concentration decreases as the vacuum degree decreases. For example, to adjust the [N] concentration to 0.05 mass%, the degree of vacuum may be set to about 40 Torr or less. The solid line in the figure is the relation obtained under the conditions of various steel types, molten steel temperature and vacuum degree. a = −1.35− {3280 / (T + 273) −0.75} (0.01 [Ni] −0.045 [Cr] +0.009)… P = 760 ([N] 2 × 10 −2a ) Fig. 2 and formula, From the formula, molten steel temperature, [N in molten steel
If the vacuum degree is adjusted according to the i] and [Cr] concentrations, N
It was confirmed that even if only two gases were blown in, it could be controlled to an arbitrary [N] concentration.
【0010】図3にSUS304ステンレス鋼を同一精
錬容器を用いて大気圧精錬後、真空精錬を実施した場合
の還元処理時の吹込みガスの全ガス中のArガスの比率
と溶鋼中[N]濃度の関係を示す。なお、吹込みガスと
してはN2 単独またはArガスとN2 ガスの混合ガスを
用いて、真空度100Torr一定状態で溶鋼トン当り
0.2Nm3 /min以上で1min以上吹込んだ後の
値であり、図中の○印が実測値で、実線は実験的に求め
られた線である。図3より[N]濃度は同一真空度にも
かかわらず、ガス中のArガスの比率が大きくなれば低
下することがわかる。図中の実線は、種々の鋼種、溶鋼
温度、吹込みガスのArガス比率および真空度の条件で
求められた関係であるが、式で表すと下記式および
式となる。
a=−1.35−{3280/(T+273)−0.75}(0.01[Ni]−0.045[Cr]+0.009) …
P=760([N]2×10-2a ) {(QAr+QN2)/QAr} ……
図3および式、式より、溶鋼温度、溶鋼中の[N
i]、[Cr]濃度および吹込みガスのArガス比率に
合わせて真空度を調整すれば、任意の[N]濃度に制御
できることが確認された。In FIG. 3, the ratio of Ar gas in the total gas of the blowing gas and the molten steel [N] in the reduction process when SUS304 stainless steel is smelted under atmospheric pressure using the same smelting vessel and then vacuum smelting is carried out. The relationship of concentration is shown. As a blowing gas, N 2 alone or a mixed gas of Ar gas and N 2 gas was used, and the value after blowing for 1 min or more at 0.2 Nm 3 / min or more per ton of molten steel at a constant vacuum degree of 100 Torr. Yes, the circles in the figure are the measured values, and the solid line is the line obtained experimentally. It can be seen from FIG. 3 that the [N] concentration decreases as the ratio of Ar gas in the gas increases, despite the same vacuum degree. The solid line in the figure is the relationship obtained under the conditions of various steel types, molten steel temperature, Ar gas ratio of the blowing gas, and degree of vacuum. a = -1.35- {3280 / (T + 273) -0.75} (0.01 [Ni] -0.045 [Cr] +0.009) ... P = 760 ([N] 2 × 10 -2a ) {(Q Ar + Q N2 ) / Q Ar } ...... From Fig. 3 and the formula, the molten steel temperature, [N
It was confirmed that the [N] concentration can be controlled arbitrarily by adjusting the degree of vacuum according to the i], [Cr] concentration and the Ar gas ratio of the blown gas.
【0011】式、式および式の関係は平均値を示
したものであり、操業においてはばらつきを考えて、N
2 ガスのみを吹込む場合には下記式と式より求まる
真空度で、またN2 ガスとArガスの混合ガスを吹込む
場合には下記式と式より求まる真空度で還元処理を
行えばよいことが確認された。
a=−1.35−{3280/(T+273)−0.75}(0.01[Ni]−0.045[Cr]+0.009) …
P≦760([N]2×10-2a ) +10 ……
P≦760([N]2×10-2a ) {(QAr+QN2)/QAr}+10 ……
図4にSUS304ステンレス鋼を同一精錬容器を用い
て大気圧精錬後、真空精錬を実施した場合に、目標
[N]濃度に合わせて、前記式、式および式より
求まる真空度で還元処理を行った場合の吹込みガス流量
と目標[N]濃度達成率の関係を示す。なお、吹込みガ
スとしてはN2 ガス単独またはN2 ガスとArガスの混
合ガスを用いて1min以上吹込み、目標[N]濃度達
成率は下記式で定義した。The equations, the equations, and the relations of the equations show average values, and in consideration of variations in the operation, N
When only 2 gases are blown, the reduction degree may be obtained by the following equation and the vacuum degree obtained by the equation, and when a mixed gas of N 2 gas and Ar gas is blown, the reduction degree may be obtained by the following equation and the vacuum degree obtained by the equation. It was confirmed. a = -1.35- {3280 / (T + 273) -0.75} (0.01 [Ni] -0.045 [Cr] +0.009)… P ≦ 760 ([N] 2 × 10 -2a ) +10 …… P ≦ 760 ( [N] 2 × 10 -2a ) {(Q Ar + Q N2 ) / Q Ar } +10 ...... In Fig. 4, the target was obtained when SUS304 stainless steel was subjected to atmospheric pressure refining using the same refining vessel and then vacuum refining. The relationship between the blowing gas flow rate and the target [N] concentration achievement rate in the case where the reduction treatment is performed according to the above equation, the equation, and the degree of vacuum obtained from the equation according to the [N] concentration is shown. It should be noted that N 2 gas alone or a mixed gas of N 2 gas and Ar gas was used as the blowing gas and was blown for 1 min or more. The target [N] concentration achievement rate was defined by the following formula.
【0012】[0012]
【数1】 [Equation 1]
【0013】図4からわかるように、吹込みガス流量の
増大とともに目標[N]濃度達成率は大きくなり、吹込
みガス流量が溶鋼トン当り0.2Nm3 /min以上で
ほぼ100%になる。従って、吹込みガス流量としては
溶鋼トン当り0.2Nm3 /min以上が必要である。
図5にSUS304ステンレス鋼を同一精錬容器を用い
て大気圧精錬後、真空精錬を実施した場合に、目標
[N]濃度に合わせて、前記式、式および式より
求まる真空度で還元処理を行った場合の該真空度での精
錬時間と目標[N]濃度達成率の関係を示す。なお、吹
込みガスとしてはN2 ガス単独またはN2 ガスとArガ
スの混合ガスを合計で溶鋼トン当り0.2Nm3 /mi
n以上で吹込んだ。As can be seen from FIG. 4, the target [N] concentration achievement rate increases as the blowing gas flow rate increases, and becomes almost 100% when the blowing gas flow rate is 0.2 Nm 3 / min or more per ton of molten steel. Therefore, the flow rate of blown gas must be 0.2 Nm 3 / min or more per ton of molten steel.
In Fig. 5, when SUS304 stainless steel is subjected to atmospheric pressure refining using the same refining vessel and then vacuum refining is performed, reduction treatment is performed according to the above formula, the formula and the degree of vacuum obtained from the formula according to the target [N] concentration. The relationship between the refining time at the degree of vacuum and the target [N] concentration achievement rate in the case of the above is shown. As the blowing gas, N 2 gas alone or a mixed gas of N 2 gas and Ar gas was added in total of 0.2 Nm 3 / mi per ton of molten steel.
I blew it over n.
【0014】図5からわかるように、精錬時間の増大で
目標[N]濃度達成率は大きくなり、精錬時間が1mi
n以上でほぼ100%になる。従って、精錬時間として
は少なくとも1minが必要である。以上より、本発明
法に従えば、同一精錬容器を用いて大気圧精錬後、真空
精錬を行う精錬法において、目標[N]濃度に合わせて
還元処理時の真空度を設定し、該真空度下で、N2 ガス
単独またはN2 ガスとArガスの混合ガスの吹込みを行
うことで目標[N]濃度に制御できることになり、効率
的な精錬が行える。また、真空精錬は鋼種によっては脱
炭精錬の不要な鋼種もあるが、この場合には還元精錬の
みを真空下で行えば、効率的な精錬が可能になる。As can be seen from FIG. 5, the target [N] concentration achievement rate increases as the refining time increases, and the refining time is 1 mi.
Almost 100% when n or more. Therefore, at least 1 min is required as the refining time. From the above, according to the method of the present invention, in the refining method of performing atmospheric pressure refining using the same refining vessel and then vacuum refining, the degree of vacuum during the reduction treatment is set according to the target [N] concentration, and the degree of vacuum is set. By blowing N 2 gas alone or a mixed gas of N 2 gas and Ar gas below, the target [N] concentration can be controlled, and efficient refining can be performed. Further, in vacuum refining, there are steel types that do not require decarburization refining depending on the type of steel, but in this case, efficient refining can be performed by performing only reduction refining under vacuum.
【0015】[0015]
【作用】溶鋼中の[N]の除去反応、つまり脱窒反応は
下記式で示され、反応平衡定数Kは式で示される。
N=1/2N2 (g) ……
K=PN2 1/2 /aN ……
ここで、PN2は雰囲気中のN2 ガスの分圧(atm)、
aN は溶鋼中[N]の活量である。The reaction for removing [N] in molten steel, that is, the denitrification reaction, is represented by the following equation, and the reaction equilibrium constant K is represented by the equation. N = 1 / 2N 2 (g) K = P N2 1/2 / a N ...... where P N2 is the partial pressure (atm) of N 2 gas in the atmosphere,
a N is the activity of [N] in the molten steel.
【0016】含クロム溶鋼では、溶鋼中に多量に含まれ
る[Cr]がaN を低下させるために[N]の溶解度が
大きくなる。目標[N]濃度まで脱窒させるためには、
PN2を低下させる手段として、真空精錬の適用および吹
込みガスをArガス単独とする方法が行われてきた。従
来より、吹込みガスとしてArガスを用いた場合の溶鋼
組成、溶鋼温度および真空度と平衡[N]濃度の関係は
種々示されているが、真空精錬下でN2 ガスあるいはN
2 ガスとArガスの混合ガスを用いた場合の溶鋼組成、
溶鋼温度および真空度と平衡[N]濃度の関係はない。
本発明者らは種々の条件での実験より、前記式、式
および式の関係を導出した。さらに、この関係を基
に、操業時の条件である式、式および式の関係を
求めた。In chromium-containing molten steel, [N] contained in a large amount in the molten steel reduces a N , so that the solubility of [N] becomes large. To denitrify to the target [N] concentration,
As means for lowering P N2 , application of vacuum refining and a method of using Ar gas alone as a blowing gas have been performed. Conventionally, molten steel composition in the case of using the Ar gas as the blown gas, the equilibrium between the molten steel temperature and vacuum degree [N] concentration relationships have been variously shown, under vacuum refining N 2 gas or N
Molten steel composition when a mixed gas of 2 gas and Ar gas is used,
There is no relationship between the molten steel temperature and the degree of vacuum and the equilibrium [N] concentration.
The present inventors derived the above equations, the equations, and the relationships of the equations from experiments under various conditions. Further, based on this relationship, the formulas, formulas, and formulas, which are the conditions during operation, were obtained.
【0017】脱窒反応は表面活性元素である溶鋼中の
[O]濃度が低下すれば速くなることは良く知られてい
る。このため、脱窒処理を脱炭精錬後の還元処理で行え
ば効率的である。しかし、これまではこの場合の吹込み
ガスとしてはArガスが用いられており、N2 ガスある
いはN2 ガスとArガスの混合ガスを用いた場合の脱窒
挙動は明確ではなかった。本発明者らは、真空下であれ
ばN2 ガスあるいはN2ガスとArガスの混合ガスを用
いた場合でも脱窒反応は進行し、前記式、式および
式で求まる真空度で還元処理を行えば、容易に目標
[N]濃度までの脱窒反応が進行することを見出した。
さらに、目標[N]濃度にまで下げるためのガス吹込み
流量および精錬時間の好適条件を見出した。It is well known that the denitrification reaction becomes faster when the [O] concentration in the molten steel, which is a surface-active element, decreases. Therefore, it is efficient to perform the denitrification treatment by the reduction treatment after the decarburization refining. However, until now, Ar gas has been used as the blowing gas in this case, and the denitrification behavior when using N 2 gas or a mixed gas of N 2 gas and Ar gas has not been clear. The inventors of the present invention have found that the denitrification reaction proceeds even when N 2 gas or a mixed gas of N 2 gas and Ar gas is used under vacuum, and the reduction treatment is performed at the vacuum degree obtained by the above formula, formula and formula. It has been found that the denitrification reaction up to the target [N] concentration easily proceeds if performed.
Furthermore, suitable conditions for the gas injection flow rate and refining time for reducing the target [N] concentration were found.
【0018】本発明法により、還元処理を開始するまで
の脱炭処理でも吹込みガスに高価なArガスを使用する
ことは不要になり、酸素の希釈ガスとしてはN2 ガスや
空気のようなN2 ガスを含む安価なガスを用いることが
可能になった。According to the method of the present invention, it is not necessary to use expensive Ar gas as a blowing gas even in the decarburization process until the reduction process is started, and as the oxygen diluting gas, N 2 gas or air such as air can be used. It has become possible to use inexpensive gases including N 2 gas.
【0019】[0019]
【実施例】SUS304ステンレス鋼(8mass%N
i−18mass%Cr)で目標の[C]濃度が0.0
5〜0.07mass%、[N]濃度が0.03〜0.
05mass%の範囲を要求される鋼60tonの処理
を図1に示す実施態様で実施した。脱炭開始時の[C]
濃度は全て1.5mass%とし、真空精錬を開始する
までは酸素または酸素と不活性ガスの混合ガスを用いて
精錬を行い、真空精錬では不活性ガスのみを用いて精錬
を行った。なお、目標[C]濃度までの脱炭処理を大気
圧下で行った場合と真空精錬で行った場合の両方で実施
した。還元処理は還元剤にFe−Siを用い、脱炭処理
で酸化した[Cr]を回収するために必要な還元剤の量
を求め、この量に製品に要求される[Si]濃度分も含
めてFe−Siの添加を行い、真空下での不活性ガスの
吹込みを行った。なお、還元処理はいずれも5min間
の処理を行った。その後、大気圧状態に戻し、取鍋に出
鋼した。[Example] SUS304 stainless steel (8 mass% N
i-18 mass% Cr) and the target [C] concentration is 0.0
5 to 0.07 mass%, and [N] concentration is 0.03 to 0.
The treatment of 60 tonnes of steel requiring a range of 05 mass% was carried out in the embodiment shown in FIG. [C] at the start of decarburization
All the concentrations were 1.5 mass%, and refining was performed using oxygen or a mixed gas of oxygen and an inert gas until the vacuum refining was started, and in the vacuum refining, refining was performed using only an inert gas. The decarburization treatment up to the target [C] concentration was performed both at atmospheric pressure and in vacuum refining. In the reduction treatment, Fe-Si was used as the reducing agent, and the amount of the reducing agent required to recover the [Cr] oxidized by the decarburization treatment was calculated. This amount also includes the [Si] concentration required for the product. Fe-Si was added thereto to blow an inert gas under vacuum. The reduction treatment was performed for 5 minutes. After that, the pressure was returned to atmospheric pressure and the steel was tapped in a ladle.
【0020】表1に脱炭処理時の真空度および還元処理
時の精錬条件の実施例を示す。本発明の実施例は先に示
した条件を満足するようにして実施した。比較例のN
o.7は還元処理を大気圧下で実施した例、比較例のN
o.8,No.9は従来例である特開平4−21486
号公報および特開平4−263005号公報記載の方法
に準じて実施した例、比較例のNo.10は処理時の到
達真空度が本発明の条件外の例、比較例のNo.11は
ガス吹込み流量が本発明の条件外の例、比較例のNo.
12は到達真空度下での精錬時間が本発明の条件外の例
である。Table 1 shows examples of vacuum degree during decarburization and refining conditions during reduction. The examples of the present invention were carried out so as to satisfy the above-mentioned conditions. Comparative example N
o. No. 7 is an example of performing reduction treatment under atmospheric pressure, N of comparative example
o. 8, No. Reference numeral 9 is a conventional example.
Nos. Of Comparative Examples and Examples carried out according to the methods described in Japanese Patent Laid-Open No. Hei 4-263005. In No. 10 of the comparative example, the ultimate vacuum during processing is outside the conditions of the present invention. No. 11 of the comparative example is the case where the gas injection flow rate is outside the conditions of the present invention.
12 is an example where the refining time under the ultimate vacuum is outside the conditions of the present invention.
【0021】実施結果を表2に示す。表中のArガス原
単位および精錬コストの値は本発明例のNo.1の結果
を100として比例換算した値である。本発明では到達
[N]濃度が目標[N]濃度0.03〜0.05mas
s%を達成し、かつArガス原単位および精錬コストと
もに低位に安定している。一方、比較例では目標[N]
濃度を達成しない例もあり、またArガス原単位および
精錬コストも高位になっている。The results of implementation are shown in Table 2. The values of the basic unit of Ar gas and the refining cost in the table are shown in No. It is a value obtained by proportionally converting the result of 1 as 100. In the present invention, the reached [N] concentration is the target [N] concentration of 0.03 to 0.05 mass.
Achieves s%, and is stable at a low level in terms of basic unit of Ar gas and refining cost. On the other hand, in the comparative example, the target [N]
In some cases, the concentration is not achieved, and the unit cost of Ar gas and refining costs are high.
【0022】[0022]
【表1】 [Table 1]
【0023】[0023]
【表2】 [Table 2]
【0024】[0024]
【発明の効果】本発明法によると、含クロム溶鋼の同一
精錬容器を用いた大気圧精錬後の真空精錬において、還
元処理をN2 ガスまたはN2 ガスとArガスの混合ガス
を用いることにより、目標[N]濃度に合わせて任意に
精錬条件を選択することが可能になり、成分外れを少な
くすることが可能になる。また、Arガスの原単位を大
幅に低減することが可能になり、精錬コストの大幅な低
減が可能になる。According to the method of the present invention, in the vacuum refining after the atmospheric refining using the same refining vessel for molten chromium-containing steel, the reduction treatment is performed by using N 2 gas or a mixed gas of N 2 gas and Ar gas. The refining conditions can be arbitrarily selected according to the target [N] concentration, and the component deviation can be reduced. In addition, it is possible to significantly reduce the basic unit of Ar gas, and it is possible to significantly reduce the refining cost.
【図1】本発明の実施態様例の精錬容器を示す図であ
る。FIG. 1 is a diagram showing a refining vessel according to an embodiment of the present invention.
【図2】本発明法におけるN2 ガス吹込みによる真空度
と[N]濃度の関係を示す図である。FIG. 2 is a diagram showing the relationship between the degree of vacuum and N concentration by blowing N 2 gas in the method of the present invention.
【図3】本発明法におけるN2 ガスとArガスの混合ガ
ス吹込みによるガス中のAr/(N2 +Ar)比と
[N]濃度の関係を示す図である。FIG. 3 is a diagram showing a relationship between an Ar / (N 2 + Ar) ratio and [N] concentration in a gas obtained by blowing a mixed gas of N 2 gas and Ar gas in the method of the present invention.
【図4】本発明法における吹込みガス流量の下限の限定
理由を示す図である。FIG. 4 is a diagram showing the reason for limiting the lower limit of the blown gas flow rate in the method of the present invention.
【図5】本発明法における精錬時間の下限の限定理由を
示す図である。FIG. 5 is a diagram showing the reason for limiting the lower limit of the refining time in the method of the present invention.
1 精錬容器 2 底吹き羽口 3 排気フード 4 溶鋼 5 ガス 1 refining container 2 Bottom blown tuyere 3 exhaust hood 4 Molten steel 5 gas
フロントページの続き (72)発明者 岩崎 央 山口県光市大字島田3434番地 新日本製 鐵株式会社光製鐵所内 (72)発明者 森重 博明 山口県光市大字島田3434番地 新日本製 鐵株式会社光製鐵所内 (56)参考文献 特開 平8−85811(JP,A) 特開 平7−188727(JP,A) 特開 平4−263005(JP,A) 特開 平4−214816(JP,A) 特開 昭58−197211(JP,A) 特開 昭51−12320(JP,A) 特開 平2−93016(JP,A) (58)調査した分野(Int.Cl.7,DB名) C21C 7/00 C21C 7/068 C21C 7/10 Front page continuation (72) Inventor, Hiroshi Iwasaki, 3434, Shimada, Hikari-shi, Yamaguchi Prefecture, Nippon Steel Co., Ltd., Hikari Steel Works (72) Inventor, Hiroaki Morishige, 3434, Shimada, Hikari-shi, Yamaguchi Prefecture, Nippon Steel Corporation (56) References JP-A-8-85811 (JP, A) JP-A-7-188727 (JP, A) JP-A-4-263005 (JP, A) JP-A-4-214816 (JP , A) JP 58-197211 (JP, A) JP 51-12320 (JP, A) JP 2-93016 (JP, A) (58) Fields investigated (Int.Cl. 7 , DB) Name) C21C 7/00 C21C 7/068 C21C 7/10
Claims (3)
炭処理後、真空下での脱炭および還元処理を行う含クロ
ム溶鋼の精錬法において、前記還元処理の吹込みガスと
して溶鋼トン当り0.2Nm3 /min以上のN2 ガス
を吹込み、かつ目標[N]濃度に合わせて下記式およ
び式を満足する真空度で少くとも1min還元処理す
ることを特徴とする含クロム溶鋼の精錬法。 a=−1.35−{3280/(T+273)−0.75}(0.01[Ni]−0.045[Cr]+0.009) … P≦760([N]2×10-2a ) +10 …… T :溶鋼温度(℃) [Ni]:溶鋼中の[Ni]濃度(mass%) [Cr]:溶鋼中の[Cr]濃度(mass%) P :還元処理時の真空度(Torr) [N] :目標[N]濃度(mass%)1. A refining method for chromium-containing molten steel, which comprises decarburizing treatment under atmospheric pressure using the same refining vessel, and then performing decarburizing and reducing treatment under vacuum, in which molten steel is used as a blowing gas for the reducing treatment. Molten chrome-containing steel characterized by injecting N 2 gas of 0.2 Nm 3 / min or more per ton and subjecting to a target [N] concentration and performing a reduction treatment for at least 1 min at a vacuum degree that satisfies the following formula and formula: Refining method. a = -1.35- {3280 / (T + 273) -0.75} (0.01 [Ni] -0.045 [Cr] +0.009) ... P ≤ 760 ([N] 2 x 10 -2a ) +10 ... T: Molten steel temperature (° C) [Ni]: [Ni] concentration in molten steel (mass%) [Cr]: [Cr] concentration in molten steel (mass%) P: Degree of vacuum during reduction treatment (Torr) [N]: Target [ N] concentration (mass%)
炭処理後、真空下での脱炭および還元処理を行う含クロ
ム溶鋼の精錬法において、前記還元処理の吹込みガスと
して溶鋼トン当り0.2Nm3 /min以上のN2 ガス
とArガスの混合ガスを吹込み、かつ目標[N]濃度に
合わせて下記式および式を満足する真空度で少くと
も1min還元処理することを特徴とする含クロム溶鋼
の精錬法。 a=−1.35−{3280/(T+273)−0.75}(0.01[Ni]−0.045[Cr]+0.009) … P≦760([N]2×10-2a ) {(QAr+QN2)/QAr}+10 …… T :溶鋼温度(℃) [Ni]:溶鋼中の[Ni]濃度(mass%) [Cr]:溶鋼中の[Cr]濃度(mass%) P :還元処理時の真空度(Torr) [N] :目標[N]濃度(mass%) QAr :Arガスの吹込み流量(Nm3 /min) QN2 :N2 ガスの吹込み流量(Nm3 /min)2. In a refining method for molten chromium-containing steel, which comprises decarburizing treatment under atmospheric pressure using the same refining vessel, followed by decarburizing and reducing treatment under vacuum, molten steel is used as a blowing gas for the reducing treatment. A mixed gas of N 2 gas and Ar gas of 0.2 Nm 3 / min or more per ton should be blown, and the reduction treatment should be performed for at least 1 min at a vacuum degree that satisfies the following formula and formula according to the target [N] concentration. Characterizing method for refining molten chromium-containing steel. a = -1.35- {3280 / (T + 273) -0.75} (0.01 [Ni] -0.045 [Cr] +0.009) ... P≤760 ([N] 2 × 10 -2a ) {(Q Ar + Q N2 ) / Q Ar } +10 ...... T: Molten steel temperature (° C) [Ni]: [Ni] concentration (mass%) in molten steel [Cr]: [Cr] concentration (mass%) in molten steel P: During reduction treatment Degree of vacuum (Torr) [N]: Target [N] concentration (mass%) Q Ar : Flow rate of Ar gas (Nm 3 / min) Q N2 : Flow rate of N 2 gas (Nm 3 / min)
炭処理後、還元処理のみを真空下で行うことを特徴とす
る請求項1または2記載の含クロム溶鋼の精錬法。3. The refining method for molten chromium-containing steel according to claim 1, wherein the decarburization treatment is carried out under the atmospheric pressure using the same refining vessel, and only the reduction treatment is performed under vacuum.
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