JP3743237B2 - Method for refining chromium-containing molten iron alloy - Google Patents
Method for refining chromium-containing molten iron alloy Download PDFInfo
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- JP3743237B2 JP3743237B2 JP35411399A JP35411399A JP3743237B2 JP 3743237 B2 JP3743237 B2 JP 3743237B2 JP 35411399 A JP35411399 A JP 35411399A JP 35411399 A JP35411399 A JP 35411399A JP 3743237 B2 JP3743237 B2 JP 3743237B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、含クロム溶融鉄合金の精錬方法に係わり、特に、ステンレス鋼等、含クロム溶鋼の溶製に有効な技術である。
【０００２】
【従来の技術】
ステンレス鋼等の含クロム溶鋼を転炉で溶製するには、予めクロム鉱石等を転炉で直接溶融還元したり、あるいは溶銑とフェロクロムとを混合してクロムを含有した高炭素濃度の溶融鉄合金（以下、含クロム溶融鉄合金という）を製造する。そして、この含クロム溶融鉄合金を同一あるいは別の転炉でさらに脱炭等の精練を行ない、目的とする組成の含クロム溶鋼としている。
【０００３】
ところで、この脱炭等の精錬に際しては、含クロム溶融鉄合金に酸素ガスを多量に吹き込むことによって、クロムが酸化されてスラグへ移行する所謂「酸化ロス」をいかに低減するかが重要である。これは、言い換えると、吹き込んだ酸素ガスが炭素の除去に利用された割合を表す「脱炭酸素効率」の向上を必要とする。そのため、含クロム溶融鉄合金の溶製に上吹き（ＬＤ）転炉を用いる場合には、酸素ガスの吹き付けをハードブロー化したり、浴を浅くするシャローバス化により、浴の撹拌力を増大して、脱炭酸素効率の向上を図っている。また、上底吹き転炉を用いる場合には、浴の撹拌をガスの底吹きで行えるので、上記ＬＤ転炉の場合よりも大きな撹拌力が得られ、ＬＤ転炉よりも高い脱炭酸素効率が得られている。なお、この底吹きによる撹拌力を増大するには、従来より、浴の深さや底吹きガス流量を大きくするのが有効と言われている。
【０００４】
【発明が解決しようとする課題】
しかしながら、本出願人の試行によれば、浴をある深さ以上にすると、脱炭酸素効率はかえって低下することが判明した。また、底吹きガスの流量の増大でも、脱炭酸素効率が低下する場合があった。さらに、ヒートサイズ（１回の精錬で処理する含クロム溶融鉄合金の重量）を一定にしてある程度の浴の深を確保しようとすると、必然的にスラグ−メタル界面積が減少してしまう。その結果、この場合には、スラグの脱硫能が低下し、脱硫率も下がるという別の問題が生じていた。
【０００５】
本発明は、かかる事情に鑑み、スラグの脱硫能を損なわずに、脱炭酸素効率を従来より向上可能な含クロム溶融鉄合金の精錬方法を提供することを目的としている。
【０００６】
【課題を解決するための手段】
発明者は、上記目的を達成するため、クロム溶融鉄合金の精錬における操業条件について鋭意研究し、鋼浴形状、つまり、浴深さとスラグ−メタル界面積との比、及び底吹きガス流量の最適化に成功し、それを本発明に具現化した。
【０００７】
すなわち、本発明は、精錬容器に保持した含クロム溶融鉄合金の浴中に、酸化性ガスを該容器の底又は側壁から吹き込み、脱炭する含クロム溶融鉄合金の精錬方法において、前記含クロム溶融鉄合金の静止浴面位置から酸化性ガスが吹き込まれる位置までの浴深さ、該含クロム溶融鉄合金の静止浴面と該浴面上に存在するスラグとの界面積及び吹き込まれる酸化性ガスの流量を、下記式を満足する範囲内に定めて精錬することを特徴とする含クロム溶融鉄合金の精錬方法である。
【０００８】
記
５≦Ｑ×Ａ／Ｈ≦２０…（１）
ここで、
Ｑ：１トン当たりの含クロム溶融鉄合金中に吹き込まれる酸化性ガスの流量（Ｎｍ3／ｔ・ｍｉｎ）、
Ａ：含クロム溶融鉄合金の静止浴面と該浴面上に存在するスラグとの界面積（ｍ2）、
Ｈ：含クロム溶融鉄合金の静止浴面位置から酸化性ガスが吹き込まれる位置までの浴深さ（ｍ）
また、本発明は、前記含クロム溶融鉄合金がクロムを５質量％以上含有することを特徴とする含クロム溶融鉄合金の精錬方法である。
【０００９】
さらに、本発明は、前記酸化性ガスが、酸素ガス又は酸素ガスと他のガスとの混合ガスであったり、あるいは前記精錬容器が、底吹き転炉、上底吹き転炉及びＡＯＤ炉から選ばれた１種であることを特徴とする含クロム溶融鉄合金の精錬方法である。
【００１０】
本発明では、操業条件の一部を最適化したので、スラグの脱硫能を損なわずに、脱炭効率を従来より向上させることができるようになった。
【００１１】
【発明の実施の形態】
以下、図面を参照して、本発明の実施の形態を説明する。
【００１２】
まず、発明者は、前記した３つの問題点、つまり
１．浴をある深さ以上にすると、脱炭酸素効率はかえって低下した、
２．底吹きガスの流量の増大でも、脱炭酸素効率が低下する場合があった、
３．ヒートサイズ（１回の精錬で処理する含クロム溶融鉄合金の重量）を一定にしてある程度の浴深を確保しようとすると、必然的にスラグ−メタル界面積が減少してしまい、その結果、スラグの脱硫能が低下する
等の内容から、浴の深さ（記号Ｈ）、底吹き酸化性ガス流量（記号Ｑ）及びスラグ−メタル界面積（記号Ａ）を操業因子に選択し、操業試験を行なった。
【００１３】
この操業試験は、精錬容器に保持した含クロム溶融鉄合金の浴中に、酸化性ガスを該容器の底又は側壁から吹き込み脱炭精練するものである。含クロム溶融鉄合金としては、前記した直接クロム鉱石を予め溶融還元したもので、クロム濃度は、５重量％以上の鉄合金、具体的には５．５重量％Ｃｒ合金、９重量％Ｃｒ合金、１３重量％Ｃｒ合金、１６重量％Ｃｒ合金及び１８重量％Ｃｒ合金である。
【００１４】
使用した精錬容器は、図２（ｂ）に示すような底吹き転炉である。しかし、本発明では、図２（ａ）に示すような底吹き転炉、あるいは図２（ｃ）に示すような、酸化性ガスを側壁からメタル浴中に吹き込む所謂ＡＯＤ炉（転炉から出鋼された溶鋼を、別途アルゴンガスを吹き込み、脱炭するのに使用する炉）を使用しても良い。
【００１５】
そして、発明者は、上記試験操業の結果を脱炭酸素効率及び脱硫率に着眼して整理した。その際、上記３つの因子は操業で同時に使用されることから、３つの因子をすべて使用して脱炭酸素効率や脱硫率との関係が表現できることに留意した。この３つの因子の組み合わせを種々試みたところ、Ｑ×（Ａ／Ｈ）なる組み合わせが最も良い整理結果になった。つまり、図１に示すように、脱炭酸素効率に対しては台形状の関係が、脱硫率に対してはГ状の関係が得られた。この関係を得るに際して使用した各因子の具体的な値のうち浴の深さやスラグ−メタル界面積については、溶融鉄合金の静止状態を基準にした。これらの値は、操業中では常に変動し、一定にならないからである。また、酸化性ガスとしては、通常の転炉操業に従い、酸素ガスを用いたが、本発明では、酸素ガスと他のガス、例えばアルゴン、窒素等の不活性ガスとの混合ガスを用いても良い。なお、脱炭酸素効率は、（脱炭に必要な理論酸素量）／（実績酸素量）として、脱硫率は、（精錬前溶湯中Ｓ濃度−精錬後溶湯中Ｓ濃度）／（精錬前溶湯中Ｓ濃度）として定義される。
【００１６】
次に、発明者は、この図１を詳細に観察し、その関係が得られた理由を以下のように考察した。
【００１７】
脱炭酸素効率がＱ×Ａ／Ｈの大きい側（２０超えの領域）で低下しているのは、吹き込みガスがあまり大きくなり過ぎると、流速が早くて吹込んだガスが浴面からすぐに抜けてしまい、攪拌がＱ×Ａ／Ｈのより小さい側よりかえって弱まる。これは、操業中に酸素ガスと浴中炭素の接触機会を減らす。また、吹抜けガスが多いと、浴中で消費しきれない酸素がスラグ相や気相の酸素ポテンシャルが高まり、メタルの酸化を促進する。この酸化は、所謂スラグ−メタル間反応なので、炭素の酸化よりもクロムの酸化に有利になり、脱炭酸素効率が低下する。なお、クロムは、一旦酸化されスラグへ移行すると、溶融鉄合金浴中に含まれる他の金属元素では還元され難い。
【００１８】
脱硫率がＱ×Ａ／Ｈの小さい側（５未満の領域）で低くなっているのは、その条件下では、浴が深くてスラグ−メタル界面積が小さいため、スラグ−メタル反応が主体の脱硫を阻害するからである。従って、図１に現れた関係は、クロムを５質量％以上と多量に含有する溶融鉄合金の酸素吹錬ほど妥当なものである。
【００１９】
そこで、発明者は、図１から導きだせる下記（１）式を、本発明の要件に採用したのである。
【００２０】
５≦Ｑ×Ａ／Ｈ≦２０…（１）
ここで、
Ｑ：１トン当たりの含クロム溶融鉄合金中に吹き込まれる酸化性ガスの流量（Ｎｍ3／ｔ・ｍｉｎ）、
Ａ：含クロム溶融鉄合金の静止浴面と該浴面上に存在するスラグとの界面積（ｍ2）、
Ｈ：含クロム溶融鉄合金の静止浴面位置から酸化性ガスが吹き込まれる位置までの浴深さ（ｍ）
【００２１】
【実施例】
処理能力１８０トンの精錬容器を用い、含クロム溶融鉄合金（Ｃｒ含有量１３〜１８重量％）を脱炭精練し、含クロム合金鋼を溶製した。その際、本発明に係る方法と表１に条件を示す従来通りの方法の２種類を採用し、操業結果を比較した。出発原料の含クロム溶融鉄合金は、事前に同一の精錬容器を用い、溶融還元法等で精錬を別途行い準備した。
【００２２】
操業結果を表１に一括して示す。表１より、本発明によれば、従来に比べて、脱硫率を損なわずに、脱炭酸素効率が格段に向上していることが明らかである。
【００２３】
【表１】
【発明の効果】
以上述べたように、本発明により、含クロム溶融鉄合金の精錬において、操業条件の一部を最適化するだけで、スラグの脱硫能を損なわずに、脱炭効率を従来より向上できるようになった。
【図面の簡単な説明】
【図１】含クロム溶融鉄合金の脱炭酸素効率及び脱硫率と本発明で新たに採用した操業因子との関係を示す図である。
【図２】本発明に係る方法を実施可能な精練容器を示す図であり、（ａ）は上底吹き転炉、（ｂ）は底吹き転炉、（ｃ）はＡＯＤ炉である。
【符号の説明】
１ 精錬容器（転炉、ＡＯＤ炉等）
２ ガスの上吹きランス
３ ガスの底吹き羽口、又はポーラスプラグ
４ 含クロム溶融鉄合金
５ スラグ
６ 酸化性ガス
７ 静止浴面位置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for refining a chromium-containing molten iron alloy, and in particular, is a technique effective for melting chromium-containing molten steel such as stainless steel.
[0002]
[Prior art]
In order to smelt chromium-containing molten steel such as stainless steel in a converter, high-concentration molten iron containing chromium is prepared by directly melting and reducing chromium ore or the like in advance in the converter, or by mixing molten iron and ferrochrome. An alloy (hereinafter referred to as a chromium-containing molten iron alloy) is manufactured. Then, this chromium-containing molten iron alloy is further refined by decarburization or the like in the same or another converter to obtain a chromium-containing molten steel having a desired composition.
[0003]
By the way, in refining such as decarburization, it is important to reduce so-called “oxidation loss” in which chromium is oxidized and transferred to slag by blowing a large amount of oxygen gas into the chromium-containing molten iron alloy. In other words, this requires an improvement in “decarbonation efficiency”, which represents the rate at which the blown oxygen gas is utilized for carbon removal. For this reason, when using an up-blow (LD) converter for melting chromium-containing molten iron alloys, the oxygen-blasting can be hard blown or the bath can be shallowed to increase the stirring power of the bath. Therefore, decarbonation efficiency is improved. Further, in the case of using the top-bottom blown converter, since the bath can be stirred by gas bottom blowing, a larger stirring force can be obtained than in the case of the LD converter, and the decarbonation efficiency is higher than that of the LD converter. Has been obtained. In order to increase the stirring force by this bottom blowing, it is conventionally said that it is effective to increase the bath depth and the bottom blowing gas flow rate.
[0004]
[Problems to be solved by the invention]
However, according to the applicant's trial, it has been found that decarboxylation efficiency decreases when the bath is deeper than a certain depth. Further, even when the flow rate of the bottom blowing gas is increased, the decarbonation efficiency may be lowered. Furthermore, if the heat size (the weight of the chromium-containing molten iron alloy processed by one refining) is made constant and an attempt is made to secure a certain bath depth, the slag-metal interface area will inevitably decrease. As a result, in this case, another problem has arisen in that the desulfurization ability of the slag decreases and the desulfurization rate also decreases.
[0005]
In view of such circumstances, an object of the present invention is to provide a method for refining a chromium-containing molten iron alloy capable of improving decarbonation efficiency as compared with the conventional one without impairing the desulfurization ability of slag.
[0006]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the inventor diligently studied the operating conditions in the refining of the chromium molten iron alloy, and optimized the steel bath shape, that is, the ratio between the bath depth and the slag-metal interface area, and the bottom blowing gas flow rate. Successfully realized and embodied in the present invention.
[0007]
That is, the present invention provides a method for refining a chromium-containing molten iron alloy in which an oxidizing gas is blown from the bottom or side wall of the vessel into a bath of the chromium-containing molten iron alloy held in a refining vessel and decarburized. The bath depth from the position of the stationary bath surface of the molten iron alloy to the position where the oxidizing gas is blown, the interfacial area between the stationary bath surface of the chromium-containing molten iron alloy and the slag existing on the bath surface, and the oxidizing property to be blown A refining method for a chromium-containing molten iron alloy characterized by refining a gas flow rate within a range satisfying the following formula.
[0008]
5 ≦ Q × A / H ≦ 20 (1)
here,
Q: Flow rate of oxidizing gas (Nm 3 / t · min) blown into chromium-containing molten iron alloy per ton,
A: Interfacial area (m 2 ) between the stationary bath surface of the chromium-containing molten iron alloy and the slag present on the bath surface,
H: Bath depth from the stationary bath surface position of the chromium-containing molten iron alloy to the position where the oxidizing gas is blown (m)
The present invention is also a method for refining a chromium-containing molten iron alloy, wherein the chromium-containing molten iron alloy contains 5% by mass or more of chromium.
[0009]
Further, in the present invention, the oxidizing gas is oxygen gas or a mixed gas of oxygen gas and another gas, or the refining vessel is selected from a bottom blowing converter, an upper bottom blowing converter, and an AOD furnace. This is a method for refining a chromium-containing molten iron alloy.
[0010]
In the present invention, since a part of the operating conditions has been optimized, the decarburization efficiency can be improved compared to the conventional one without impairing the desulfurization ability of the slag.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0012]
First, the inventor made the above three problems, namely, 1. When the bath was deeper than a certain depth, the decarbonation efficiency was reduced.
2. Even if the flow rate of the bottom blowing gas was increased, the decarbonation efficiency could decrease.
3. An attempt to ensure a certain bath depth with a constant heat size (the weight of the chromium-containing molten iron alloy processed by one refining) will inevitably reduce the slag-metal interface area, resulting in slag. Select the bath depth (symbol H), bottom-blowing oxidizing gas flow rate (symbol Q) and slag-metal interface area (symbol A) as the operating factors from the contents such as the desulfurization ability of the oil is reduced. I did it.
[0013]
In this operation test, an oxidizing gas is blown from the bottom or the side wall of a chromium-containing molten iron alloy held in a refining vessel and decarburized and refined. The chromium-containing molten iron alloy is obtained by previously melting and reducing the above direct chromium ore, and the chromium concentration is 5% by weight or more of iron alloy, specifically 5.5% by weight Cr alloy, 9% by weight Cr alloy. 13 wt% Cr alloy, 16 wt% Cr alloy and 18 wt% Cr alloy.
[0014]
The refining vessel used is a bottom blow converter as shown in FIG. However, in the present invention, a bottom blowing converter as shown in FIG. 2 (a) or a so-called AOD furnace (from the converter) in which an oxidizing gas is blown into the metal bath from the side wall as shown in FIG. 2 (c). A furnace used to decarburize the molten steel by blowing argon gas separately may be used.
[0015]
And the inventor arranged the result of the said test operation paying attention to decarbonation efficiency and desulfurization rate. At that time, since the above three factors are used simultaneously in the operation, it was noted that the relationship between the decarbonation efficiency and the desulfurization rate can be expressed by using all the three factors. When various combinations of these three factors were tried, the combination of Q × (A / H) gave the best organizing result. That is, as shown in FIG. 1, a trapezoidal relationship was obtained for the decarbonation efficiency and a Γ relationship was obtained for the desulfurization rate. Of the specific values of the factors used to obtain this relationship, the bath depth and the slag-metal interface area were based on the stationary state of the molten iron alloy. This is because these values always fluctuate during operation and do not become constant. Further, as the oxidizing gas, oxygen gas was used in accordance with normal converter operation. However, in the present invention, a mixed gas of oxygen gas and another gas, for example, an inert gas such as argon or nitrogen may be used. good. The decarbonation efficiency is (theoretical oxygen amount necessary for decarburization) / (actual oxygen amount), and the desulfurization rate is (S concentration in molten metal before refining−S concentration in molten metal after refining) / (melt before molten). Medium S concentration).
[0016]
Next, the inventors observed this FIG. 1 in detail and considered the reason why the relationship was obtained as follows.
[0017]
The decarbonation efficiency decreases on the large side of Q × A / H (region exceeding 20). If the blown gas becomes too large, the flow rate is too fast and the blown gas is immediately discharged from the bath surface. And the stirring is weakened from the smaller side of Q × A / H. This reduces the chance of contact between oxygen gas and carbon in the bath during operation. In addition, when there are many blow-by gases, oxygen that cannot be consumed in the bath increases the oxygen potential of the slag phase and gas phase, and promotes metal oxidation. Since this oxidation is a so-called slag-metal reaction, it is more advantageous for the oxidation of chromium than the oxidation of carbon, and the decarbonation efficiency is lowered. In addition, once chromium is oxidized and moves to slag, it is difficult to reduce by other metal elements contained in the molten iron alloy bath.
[0018]
The reason why the desulfurization rate is lower on the smaller side of Q × A / H (region less than 5) is that under the conditions, the bath is deep and the slag-metal interface area is small. It is because desulfurization is inhibited. Accordingly, the relationship appearing in FIG. 1 is more appropriate for oxygen blowing of a molten iron alloy containing a large amount of chromium at 5 mass% or more.
[0019]
Therefore, the inventor adopted the following expression (1) derived from FIG. 1 as the requirement of the present invention.
[0020]
5 ≦ Q × A / H ≦ 20 (1)
here,
Q: Flow rate of oxidizing gas (Nm 3 / t · min) blown into chromium-containing molten iron alloy per ton,
A: Interfacial area (m 2 ) between the stationary bath surface of the chromium-containing molten iron alloy and the slag present on the bath surface,
H: Bath depth from the stationary bath surface position of the chromium-containing molten iron alloy to the position where the oxidizing gas is blown (m)
[0021]
【Example】
Using a smelting vessel with a processing capacity of 180 tons, chromium-containing molten iron alloy (Cr content: 13 to 18% by weight) was decarburized and smelted to produce chromium-containing alloy steel. At that time, the method according to the present invention and the conventional method whose conditions are shown in Table 1 were adopted, and the operation results were compared. The chromium-containing molten iron alloy as a starting material was prepared in advance by separately refining it using a smelting reduction method using the same refining vessel.
[0022]
The operation results are collectively shown in Table 1. From Table 1, it is clear that according to the present invention, the decarbonation efficiency is remarkably improved without impairing the desulfurization rate as compared with the conventional case.
[0023]
[Table 1]
【The invention's effect】
As described above, according to the present invention, in the refining of the chromium-containing molten iron alloy, it is possible to improve the decarburization efficiency as compared with the conventional one without losing the desulfurization ability of the slag only by optimizing a part of the operating conditions. became.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between decarbonation efficiency and desulfurization rate of a chromium-containing molten iron alloy and operating factors newly adopted in the present invention.
FIG. 2 is a view showing a scouring vessel capable of performing the method according to the present invention, wherein (a) is an upper bottom blowing converter, (b) is a bottom blowing converter, and (c) is an AOD furnace.
[Explanation of symbols]
1 Refining vessel (converter, AOD furnace, etc.)
2 Gas
Claims (4)
前記含クロム溶融鉄合金の静止浴面位置から酸化性ガスが吹き込まれる位置までの浴深さ、該含クロム溶融鉄合金の静止浴面と該浴面上に存在するスラグとの界面積及び吹き込まれる酸化性ガスの流量を、下記式を満足する範囲内に定めて精錬することを特徴とする含クロム溶融鉄合金の精錬方法。
記
５≦Ｑ×Ａ／Ｈ≦２０…（１）
ここで、
Ｑ：１トン当たりの含クロム溶融鉄合金中に吹き込まれる酸化性ガスの流量（Ｎｍ3／ｔ・ｍｉｎ）、
Ａ：含クロム溶融鉄合金の静止浴面と該浴面上に存在するスラグとの界面積（ｍ2）、
Ｈ：含クロム溶融鉄合金の静止浴面位置から酸化性ガスが吹き込まれる位置までの浴深さ（ｍ）In the refining method of the chromium-containing molten iron alloy, the oxidizing gas is blown into the bath of the chromium-containing molten iron alloy held in the refining vessel from the bottom or side wall of the vessel and decarburized.
The bath depth from the position of the stationary bath surface of the chromium-containing molten iron alloy to the position where the oxidizing gas is blown, the interfacial area between the stationary bath surface of the chromium-containing molten iron alloy and the slag present on the bath surface, and the blowing A refining method for a chromium-containing molten iron alloy characterized by refining the flow rate of oxidizing gas within a range satisfying the following formula.
5 ≦ Q × A / H ≦ 20 (1)
here,
Q: Flow rate of oxidizing gas (Nm 3 / t · min) blown into chromium-containing molten iron alloy per ton,
A: Interfacial area (m 2 ) between the stationary bath surface of the chromium-containing molten iron alloy and the slag present on the bath surface,
H: Bath depth from the stationary bath surface position of the chromium-containing molten iron alloy to the position where the oxidizing gas is blown (m)
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