JP4833889B2 - Desulfurization method for chromium-containing molten iron - Google Patents

Desulfurization method for chromium-containing molten iron Download PDF

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JP4833889B2
JP4833889B2 JP2007055852A JP2007055852A JP4833889B2 JP 4833889 B2 JP4833889 B2 JP 4833889B2 JP 2007055852 A JP2007055852 A JP 2007055852A JP 2007055852 A JP2007055852 A JP 2007055852A JP 4833889 B2 JP4833889 B2 JP 4833889B2
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雄司 小川
直樹 平嶋
幹男 府高
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本発明は、含クロム鋼の製造において、低硫黄濃度の含クロム鋼を製造する方法に関する。   The present invention relates to a method for producing a chromium-containing steel having a low sulfur concentration in the production of chromium-containing steel.

含クロム鋼の製造プロセスを大別すると次の3つに分けられる。1つ目は、高炉溶銑を用いて、転炉でFe−Crを投入しながら粗脱炭を行い、AODまたはVOD等で脱炭精錬を行うプロセス。2つ目は、スクラップやFe−Cr等の合金鉄を主原料として電気炉で溶解し、その後脱炭精錬を行うプロセス。3つ目は、Cr鉱石を溶融還元しながら粗溶鋼(溶銑)を溶製し、その後脱炭精錬を行うプロセスである。   The manufacturing process of chromium-containing steel can be roughly divided into the following three. The first is a process in which rough decarburization is performed using Fe-Cr in the converter using blast furnace hot metal, and decarburization and refining is performed using AOD or VOD. The second is a process in which scrap iron and alloy iron such as Fe-Cr are melted in an electric furnace as the main raw material and then decarburized and refined. The third is a process in which crude molten steel (molten metal) is melted while melting or reducing Cr ore, followed by decarburization refining.

脱硫精錬は、基礎式がCaO+→CaS+と表されることからもわかるように、通常のプロセスにおいては還元精錬であり、溶鋼中の酸素活量が低いほど反応が起こりやすい。従って、普通鋼においてもそうであるが、脱炭後の低炭素溶鋼よりも炭素濃度が高い溶銑段階の方が脱硫効率が高い。更に、含クロム溶鋼の場合、メタル中CrがCの活量を低下させるため、低炭素領域での酸素活量は普通鋼に比べてより高く、Sの活量もCr濃度の増加により低下するため、上記含クロム鋼製造プロセスにおける粗脱炭後や最終脱炭後での脱硫は困難となる。そのため、SiやAl等の還元、脱酸剤を用いて、できるだけ溶鋼中の酸素活量を低下させた上で脱硫を行う必要があるが、それでも脱硫効率は高いとは言えず、脱硫フラックスやスラグの融点を低下させて脱硫能を向上させる蛍石(CaF2)を使用するのが一般的であり、Fの溶出規制から処理後スラグの資源化に課題があった。また、還元、脱酸のための合金コストも高く、経済的な課題もあった。 As can be seen from the fact that the basic formula is expressed as CaO + S → CaS + O , desulfurization refining is reductive refining in a normal process, and the reaction is more likely to occur as the oxygen activity in the molten steel is lower. Therefore, as is the case with ordinary steel, the desulfurization efficiency is higher in the hot metal stage where the carbon concentration is higher than in the low carbon molten steel after decarburization. Furthermore, in the case of chromium-containing molten steel, since Cr in the metal lowers the activity of C, the oxygen activity in the low carbon region is higher than that of ordinary steel, and the activity of S also decreases with an increase in Cr concentration. Therefore, desulfurization after rough decarburization or after final decarburization in the chromium-containing steel manufacturing process becomes difficult. Therefore, it is necessary to perform desulfurization after reducing the oxygen activity in the molten steel as much as possible using a reduction or deoxidizer such as Si or Al. However, the desulfurization efficiency is still not high, and desulfurization flux and It is common to use fluorite (CaF 2 ), which lowers the melting point of slag and improves the desulfurization ability, and there has been a problem in recycling slag after treatment due to F elution regulation. Moreover, the alloy cost for reduction | restoration and deoxidation is also high, and there existed an economical subject.

そのため、含クロム鋼製造プロセスのうち上述の1つ目の高炉溶銑を用いるプロセスにおいては、Cr分を未だ添加する前の普通溶銑段階で脱硫する方式を採用している。しかし、その場合脱硫効率が高いものの、後工程でFe−Cr等の原料を添加する場合に、原料のFe−CrがSを含有しており、Fe−CrからのSピックアップが生じることになる。このような現象を回避するため、S含有量の低い高価なFe−Crの使用を余儀なくされている。即ちS濃度制約などが生じ、原料自由度の低いプロセスとなる課題があった。   Therefore, in the process using the first blast furnace hot metal described above in the chromium-containing steel manufacturing process, a method of desulfurization is adopted in the normal hot metal stage before adding the Cr content. However, in this case, although the desulfurization efficiency is high, when a raw material such as Fe—Cr is added in the subsequent process, the raw material Fe—Cr contains S, and S pickup from Fe—Cr occurs. . In order to avoid such a phenomenon, expensive Fe—Cr having a low S content is forced to be used. That is, there is a problem that the S concentration restriction is caused and the process becomes a low degree of freedom of raw materials.

Cr原料を添加した後の炭素濃度の高い含クロム溶銑段階での脱硫方法としては、次のような方法が提案されている。   As a desulfurization method in the chromium-containing hot metal stage with a high carbon concentration after adding the Cr raw material, the following method has been proposed.

特許文献1には、溶融還元工程の後、Crを10〜20%含有する高炭素の溶銑を出湯し、脱硫材を添加して脱硫した後、脱炭炉に装入して脱炭する方法が記載されている。しかしながら、この方法は、含クロム鋼製造プロセスのうち上述の3つめの溶融還元法であり、もともと溶鉄原料中のS含有量が少ない。Cr源としてFe−Crも用いない。そのため、同文献の実施例においても脱硫前の溶鉄中S濃度が0.012%と低いのであるが、それにもかかわらず、脱硫効率が安定しない上に、脱硫能を向上させる蛍石を使用しないと脱硫が不十分となる課題があった。鉄源としてS濃度の高い高炉溶銑を用い、さらにCr源としてSを含有するFe−Crを用いる場合には、Crを含有し脱硫前のS濃度が高いのでなおらさ、蛍石なしで脱硫することは困難である。   Patent Document 1 discloses a method in which after a smelting reduction step, hot carbon containing 10 to 20% of Cr is discharged, desulfurized by adding a desulfurizing material, and then charged in a decarburizing furnace. Is described. However, this method is the above-mentioned third smelting reduction method in the chromium-containing steel production process, and originally the S content in the molten iron raw material is low. Fe-Cr is not used as a Cr source. Therefore, even in the examples of the same document, the S concentration in molten iron before desulfurization is as low as 0.012%. Nevertheless, desulfurization efficiency is not stable and fluorite that improves desulfurization ability is not used. And there was a problem that desulfurization was insufficient. When using a blast furnace hot iron with a high S concentration as the iron source and using Fe-Cr containing S as the Cr source, it contains Cr and has a high S concentration before desulfurization, so it is desulfurized without fluorite. It is difficult.

また、特許文献2や3には、電気アーク炉でCrを10〜35%含有する溶銑とスラグを生成させ、取鍋にスラグとともに出湯し、非酸化性雰囲気条件下で不活性ガス攪拌して脱硫精錬を行う方法が記載されている。しかしながら、電気炉スラグにはSiO2が相当量含まれており、スラグ中のSiO2は脱硫能を著しく低下させることが知られている。そのため、電気炉スラグを用いて脱硫するためには、非酸化性雰囲気条件下で不活性ガス攪拌して酸素ポテンシャルを下げたとしても相当量のスラグを必要とする。そのため、攪拌を行ったときのスラグの飛散やそれを防止するため処理量が低下する課題がある。また、スラグの脱硫能を上げるためにはCaO/SiO2を増加する必要があるが、その場合スラグの融点が上昇するため、著しく高い温度で電気炉から出湯するか、スラグの融点を低下させる蛍石を使用しないと、スラグが電気炉内に相当量残り、操業障害や取鍋での脱硫能低下の課題もあった。 In Patent Documents 2 and 3, hot metal and slag containing 10 to 35% of Cr are produced in an electric arc furnace, and the ladle is poured out together with the slag, and stirred with an inert gas under non-oxidizing atmosphere conditions. A method for performing desulfurization refining is described. However, the electric furnace slag contains SiO 2 is a considerable amount, SiO 2 in the slag is known to significantly reduce the desulfurization ability. Therefore, to desulfurize using electric furnace slag, a considerable amount of slag is required even if the oxygen potential is lowered by stirring with an inert gas under non-oxidizing atmosphere conditions. Therefore, there is a problem that the amount of processing is reduced in order to prevent scattering of slag when stirring is performed or to prevent it. Moreover, in order to increase the desulfurization ability of slag, it is necessary to increase CaO / SiO 2 , but in this case, the melting point of slag rises, so that hot water is discharged from an electric furnace at a significantly high temperature or the melting point of slag is lowered. If fluorite was not used, a considerable amount of slag remained in the electric furnace, and there were problems such as operational problems and reduced desulfurization capacity in the ladle.

特許文献4には、溶解炉内の溶銑にCaO源、SiO2源、Al23源を装入して低融点スラグを生成させることで、蛍石の使用量を少なくしてF溶出を規制値以下にするとともに脱硫とCr還元を促進する方法が記載されている。しかしながら、この方法においてもスラグ中のSiO2は脱硫能を著しく低下させるため、SiO2を含有するスラグでの脱硫能は低い。また、電気炉内の攪拌力は弱いために脱硫効率が低下し、0.005%以下の極低硫鋼を製造できないという課題があった。 In Patent Document 4, a CaO source, a SiO 2 source, and an Al 2 O 3 source are charged into the molten iron in the melting furnace to generate low melting point slag, thereby reducing the amount of fluorite used and elution of F. A method is described in which desulfurization and Cr reduction are promoted while being below the regulation value. However, even in this method, SiO 2 in the slag remarkably lowers the desulfurization ability, so the desulfurization ability in the slag containing SiO 2 is low. Moreover, since the stirring force in the electric furnace is weak, the desulfurization efficiency is lowered, and there is a problem that it is not possible to produce an ultra-low sulfur steel of 0.005% or less.

なお、クロムをほとんど含有しない普通溶銑の脱硫においては、機械攪拌方式による脱硫方法も一般的な方法の一つである。普通溶銑の脱硫の場合には、特許文献5に記載されているように、脱硫剤の処理温度での液相率を5〜30%として、適度な固相部分と液相部分の存在により、最も脱硫剤が巻き込まれやすい粒度に造粒させ、かつ地鉄もそこに取り込むことで見かけ比重を増加させて、より巻き込まれやすくするのが効率の良い脱硫方法とされている。   Incidentally, in the desulfurization of ordinary hot metal containing almost no chromium, a desulfurization method using a mechanical stirring method is one of the general methods. In the case of desulfurization of normal hot metal, as described in Patent Document 5, the liquid phase ratio at the treatment temperature of the desulfurizing agent is 5 to 30%, and due to the presence of an appropriate solid phase portion and liquid phase portion, It is considered as an efficient desulfurization method to granulate to a particle size in which the desulfurization agent is most easily involved and to increase the apparent specific gravity by incorporating the base iron therein so that the desulfurization agent is more easily involved.

特開平2−232312号公報JP-A-2-23212 特開平9−241716号公報JP-A-9-241716 特開平10−176214号公報JP-A-10-176214 特開2001−342510号公報JP 2001-342510 A 特開2003−213313号公報JP 2003-213313 A

含クロム溶鉄を脱硫する場合、フラックスの脱硫能を高めると同時にフラックスやスラグの融点を低下させて脱硫効率を向上させるために、蛍石(CaF2)を使用するのが一般的であったが、Fの溶出規制から処理後の資源化に課題があった。 When desulfurizing chromium-containing molten iron, it was common to use fluorite (CaF 2 ) to improve the desulfurization efficiency by increasing the desulfurization ability of the flux and simultaneously lowering the melting point of the flux and slag. From the elution regulation of F, there was a problem in recycling resources after processing.

特許文献5に示されているような固相率の高いフラックスでの脱硫を含クロム溶銑の鍋脱硫にそのまま適用した場合、機械攪拌方式、底吹き攪拌方式、フラックス吹き込み(インジェクション)方式のいずれの場合でも、処理中に空気酸化したクロムが還元されにくく、また高クロム濃度の地鉄もスラグ中に噛み込むため、結果的に処理後のスラグ中クロム濃度が高くなる。そのため、クロム分のロスとなるとともに、クロム溶出規制から処理後スラグの資源化に課題があった。   When desulfurization with a flux having a high solid phase ratio as shown in Patent Document 5 is applied as it is to pan desulfurization of chromium-containing hot metal, any of the mechanical stirring method, bottom blowing stirring method, and flux blowing (injection) method Even in this case, chromium oxidized in the air during the treatment is difficult to be reduced, and the high-chromium-contained iron is also caught in the slag. As a result, the chromium concentration in the slag after the treatment becomes high. For this reason, there was a problem in recycling slag after treatment due to loss of chromium content due to chromium elution regulation.

本発明は、高濃度のクロムを含有する鋼を製造する場合でも、脱硫フラックスに蛍石を用いずに効率良く脱硫を行い、低硫黄濃度の含クロム鋼を安定して製造する方法を提供することを課題とする。さらには、脱硫フラックスに蛍石を用いずに処理後のスラグ中クロム濃度を低減することによって、脱硫スラグの資源化を可能にする方法を提供することを課題とする。   The present invention provides a method for stably producing a low sulfur concentration chromium-containing steel by efficiently performing desulfurization without using fluorite as a desulfurization flux even when producing a steel containing high concentration chromium. This is the issue. It is another object of the present invention to provide a method for enabling desulfurization slag to be recycled by reducing the chromium concentration in the slag after treatment without using fluorite in the desulfurization flux.

かかる課題を解決するため、本発明の要旨とするところは、以下の通りである。
(1)クロムを10質量%以上50質量%以下含有し、炭素を2.5質量%以上10質量%以下含有する含クロム溶鉄を脱硫精錬前温度1250℃以上1700℃以下で脱硫精錬するに際し、脱硫前精錬炉で出湯後の脱硫精錬前温度T(℃)と溶鉄中クロム濃度CR(質量%)に対して(1)式を満足するように溶鉄中炭素濃度C(質量%)を調整する第1の工程と、脱硫精錬後のスラグ中SiO2濃度が10質量%未満となるように脱硫前精錬炉からのスラグ混入量を抑制して取鍋に出湯する第2の工程と、F濃度が1質量%以下の脱硫フラックスを使用して取鍋内で脱硫精錬する第3の工程を有することを特徴とする、含クロム溶鉄の脱硫方法。
C≧0.11×CR+15000/(T+273)−6.16 (1)
(2)脱硫精錬前温度T(℃)が1400℃以上であり、脱硫フラックスのCaO濃度(質量%)(以下「CA」ともいう。)とAl23濃度(質量%)(以下「AL」ともいう。)、およびMgO濃度(質量%)(以下「MG」ともいう。)とTとの関係が下記(2)〜(3)式を満たすことを特徴とする上記(1)記載の含クロム溶鉄の脱硫方法。
−0.000375T+0.91≦AL/(CA+AL)≦−0.000375T+1.06 (2)
CA+AL+MG≧90 (3)
(3)MgOを5質量%以上20質量%以下含有する脱硫フラックスを使用することを特徴とする、上記(2)記載の含クロム溶鉄の脱硫方法。
なお、脱硫フラックス中の金属Alは、Al23に換算して上記ALに含まれる。
(4)脱硫フラックスを使用して取鍋内で脱硫精錬するに際し、取鍋内の溶鉄を攪拌することを特徴とする上記(1)乃至(3)のいずれかに記載の含クロム溶鉄の脱硫方法。
(5)含クロム溶鉄中のクロム源としてFe−Crを用いることを特徴とする上記(1)乃至(4)のいずれかに記載の含クロム溶鉄の脱硫方法。
In order to solve this problem, the gist of the present invention is as follows.
(1) When desulfurizing and refining chromium-containing molten iron containing 10% to 50% by mass of chromium and 2.5% to 10% by mass of carbon at a pre-desulfurization temperature of 1250 ° C. to 1700 ° C., Adjust carbon concentration C (mass%) in molten iron so that the formula (1) is satisfied with respect to temperature T (° C.) before desulfurization and chrome concentration CR (mass%) in molten iron in the smelting furnace before desulfurization. A first step, a second step of controlling the amount of slag from the smelting furnace before desulfurization so that the SiO 2 concentration in the slag after desulfurization refining is less than 10% by mass, and pouring hot water into the ladle; Has a third step of desulfurizing and refining in a ladle using a desulfurization flux of 1% by mass or less.
C ≧ 0.11 × CR + 15000 / (T + 273) −6.16 (1)
(2) The temperature T (° C.) before desulfurization refining is 1400 ° C. or higher, and the CaO concentration (mass%) (hereinafter also referred to as “CA”) and the Al 2 O 3 concentration (mass%) (hereinafter “AL”) of the desulfurization flux. And the relationship between the MgO concentration (mass%) (hereinafter also referred to as “MG”) and T satisfies the following formulas (2) to (3). Desulfurization method for chromium-containing molten iron.
−0.000375T + 0.91 ≦ AL / (CA + AL) ≦ −0.000375T + 1.06 (2)
CA + AL + MG ≧ 90 (3)
(3) The desulfurization method for molten iron containing chromium according to (2) above, wherein a desulfurization flux containing 5% by mass or more and 20% by mass or less of MgO is used.
The metal Al in the desulfurization flux is included in the AL in terms of Al 2 O 3 .
(4) When desulfurizing and refining in a ladle using a desulfurization flux, the molten iron in the ladle is agitated, and the desulfurization of molten iron containing chromium according to any one of (1) to (3) above Method.
(5) The method for desulfurizing chromium-containing molten iron according to any one of (1) to (4) above, wherein Fe-Cr is used as a chromium source in the chromium-containing molten iron.

本発明により、高濃度のクロムを含有する鋼を製造する場合において、クロムを含有した後の溶鉄を脱硫するのでS濃度の高いFe−CrをCr源として使用することができ、脱硫フラックス中に蛍石を含まないので、処理後のスラグが資源化しやすい脱硫フラックスを用いて効率良い脱硫ができ、低硫黄濃度の含クロム鋼を安定して製造することが可能となった。   According to the present invention, when producing steel containing high concentration of chromium, the molten iron after containing chromium is desulfurized, so Fe-Cr having a high S concentration can be used as a Cr source, and in the desulfurization flux Since it does not contain fluorite, it can be efficiently desulfurized using a desulfurization flux that makes slag after treatment easy to be resourced, and it has become possible to stably produce chromium-containing steel having a low sulfur concentration.

本発明者らは、クロムを10質量%以上50質量%以下含有する溶鋼の種々の脱硫実験と熱力学計算を行い、溶鉄の脱硫が十分進行するために必要な炭素濃度と温度範囲を特定した。その結果、還元反応である脱硫反応が十分進行するためには、クロム濃度に応じて炭素濃度を増加させて溶鋼の酸素活量を十分低下させる必要があること、クロムと炭素の濃度に応じて精錬温度を十分に高めておく必要があることを知見した。一般に溶鉄中含有成分と脱硫能との関係は成分含有量の一次式で表せることが多い。本実験結果によれば、溶鉄中炭素濃度と脱硫能との関係は炭素濃度の一次関数で表すことができ、クロム濃度と脱硫能との関係もクロム濃度の一次関数で表すことができることがわかった。また、溶鉄温度と化学反応効率との関係は一般的に溶鉄の絶対温度の逆数で表現できることが多いが、本実験結果においても溶鉄温度と脱硫能との関係は溶鉄の絶対温度の逆数に比例することが判明した。そして、等価な脱硫効率を得るためには、クロム濃度と炭素濃度との関係は一次の関係で整理することができ、実験結果によればクロム濃度1質量%と炭素濃度0.11質量%が等価である。また、等価な脱硫効率を得るための溶鉄温度と炭素濃度との関係は、溶鉄絶対温度の逆数と炭素濃度とが一次の関係で整理できることを見出した。さらに、脱硫フラックス中に蛍石を用いずに所定の脱硫効率を得るためには、溶鉄中炭素濃度、クロム濃度と脱硫精錬前温度の関係は下記(1)式で規定されることを知見した。
C≧0.11×CR+15000/(T+273)−6.16 (1)
ここで、C:溶鉄中炭素濃度(質量%)
CR:溶鉄中クロム濃度(質量%)
T:脱硫精錬前温度(℃)
The present inventors conducted various desulfurization experiments and thermodynamic calculations on molten steel containing 10 mass% or more and 50 mass% or less of chromium, and identified the carbon concentration and temperature range necessary for the desulfurization of molten iron to proceed sufficiently. . As a result, in order for the desulfurization reaction, which is a reduction reaction, to proceed sufficiently, it is necessary to increase the carbon concentration according to the chromium concentration to sufficiently reduce the oxygen activity of the molten steel, and according to the chromium and carbon concentrations. It was found that the refining temperature needs to be raised sufficiently. In general, the relationship between the component contained in the molten iron and the desulfurization ability is often expressed by a linear expression of the component content. According to the results of this experiment, the relationship between the carbon concentration in molten iron and the desulfurization ability can be expressed by a linear function of the carbon concentration, and the relationship between the chromium concentration and the desulfurization ability can also be expressed by a linear function of the chromium concentration. It was. In general, the relationship between molten iron temperature and chemical reaction efficiency can often be expressed as the reciprocal of the absolute temperature of molten iron, but the relationship between molten iron temperature and desulfurization capacity is proportional to the reciprocal of the absolute temperature of molten iron. Turned out to be. In order to obtain equivalent desulfurization efficiency, the relationship between the chromium concentration and the carbon concentration can be arranged by a primary relationship. According to the experimental results, the chromium concentration is 1% by mass and the carbon concentration is 0.11% by mass. Is equivalent. It was also found that the relationship between the molten iron temperature and the carbon concentration for obtaining equivalent desulfurization efficiency can be arranged in a linear relationship between the reciprocal of the molten iron absolute temperature and the carbon concentration. Furthermore, in order to obtain a predetermined desulfurization efficiency without using fluorite in the desulfurization flux, it has been found that the relationship between the carbon concentration in molten iron, the chromium concentration and the temperature before desulfurization refining is defined by the following equation (1). .
C ≧ 0.11 × CR + 15000 / (T + 273) −6.16 (1)
Where C: carbon concentration in molten iron (mass%)
CR: Cr concentration in molten iron (% by mass)
T: Temperature before desulfurization refining (° C)

この(1)式で規定される含クロム溶鉄を脱硫するために適正な範囲は、溶鉄中クロム濃度に応じて図1に示す実線よりも上の範囲で示される。なお、炭素濃度と脱硫精錬前温度の組み合わせでは、クロム濃度によっては融点に到達せず、鉄が完全液相とならない場合がある(本発明では溶鉄の液相率100%が必要)。その条件は避けるように、炭素濃度と温度の設定を行う。   An appropriate range for desulfurizing the chromium-containing molten iron defined by the formula (1) is shown in a range above the solid line shown in FIG. 1 according to the chromium concentration in the molten iron. In the combination of the carbon concentration and the temperature before desulfurization refining, the melting point may not be reached depending on the chromium concentration, and iron may not become a complete liquid phase (in the present invention, the liquid phase ratio of molten iron is required to be 100%). The carbon concentration and temperature are set to avoid this condition.

脱硫精錬前温度が1250℃未満の場合には、いずれのクロム濃度においても鉄の融点未満となり、鉄が完全液相とならない。また、脱硫精錬前温度が1700℃超の場合は、脱硫方式に機械式攪拌を採用する場合のインペラーや粉体インジェクションを採用する場合の浸漬ノズルあるいは取鍋自体の耐火物溶損が激しく、脱硫操業に適さないことも知見した。また、炭素濃度が2.5%未満では、図1から分かるように、いずれのクロム濃度においても脱硫精錬前温度が1700℃以下では脱硫に適正な条件とならないこと、更に、炭素濃度が10質量%超では、いずれのクロム濃度においても鉄の融点が1700℃超となり、脱硫操業が不可能となることも判明した。   When the temperature before desulfurization refining is less than 1250 ° C., it becomes less than the melting point of iron at any chromium concentration, and iron does not become a complete liquid phase. In addition, when the temperature before desulfurization refining is higher than 1700 ° C, the refractory material of the immersion nozzle or ladle itself when the mechanical stirring is used for the desulfurization method or when the powder injection is used is severely damaged by desulfurization. It was also found that it was not suitable for operation. In addition, when the carbon concentration is less than 2.5%, as can be seen from FIG. 1, at any chromium concentration, if the temperature before desulfurization refining is 1700 ° C. or less, the conditions are not suitable for desulfurization, and the carbon concentration is 10 mass. Above%, it was also found that the melting point of iron exceeded 1700 ° C. at any chromium concentration, making desulfurization operation impossible.

また、耐火物溶損やエネルギー最小化の観点から、鉄が完全に溶融状態にある限り、できるだけ低い温度での脱硫精錬が望ましい。溶鉄温度を1500℃未満とすると好ましい。   Further, from the viewpoint of refractory melting and energy minimization, desulfurization refining at the lowest possible temperature is desirable as long as iron is in a completely molten state. The molten iron temperature is preferably less than 1500 ° C.

前述の通り、クロムを高濃度で含有する溶鉄は脱硫が難しく、溶鉄温度を高くして脱硫効率を上げることによってはじめて良好な脱硫を可能にしていた。それに対し本発明においては、溶鉄温度が低い場合でも、上記(1)式に基づいて溶鉄中の炭素濃度を上昇させることにより、脱硫に不利である溶鉄温度1500℃未満での含クロム溶鉄の脱硫を可能にすることができた。   As described above, molten iron containing chromium at a high concentration is difficult to desulfurize, and good desulfurization was enabled only by raising the molten iron temperature to increase the desulfurization efficiency. On the other hand, in the present invention, even when the molten iron temperature is low, desulfurization of molten iron containing chromium at a molten iron temperature of less than 1500 ° C., which is disadvantageous for desulfurization, by increasing the carbon concentration in the molten iron based on the above formula (1). Could be made possible.

かくして、十分な脱硫が可能となる溶鉄中の酸素活量、脱硫反応温度となるよう炭素濃度と温度を適切に調整した溶鉄を、取鍋に排出した後、脱硫フラックスを添加し、脱硫精錬を行うことで、低濃度域までの脱硫が安定して行えることが判明した。   Thus, after the molten iron with the carbon concentration and temperature adjusted appropriately to achieve the desulfurization reaction temperature, the oxygen activity in the molten iron that enables sufficient desulfurization is discharged to the ladle, and then the desulfurization flux is added to perform desulfurization refining. It was found that desulfurization up to a low concentration range can be performed stably.

脱硫方式としては、フラックスを上部から添加した後の機械攪拌方式やガス底吹き攪拌方式あるいは粉体フラックスのインジェクション方式のいずれでも良いが、脱硫効率の観点からは機械攪拌方式もしくはインジェクション方式が望ましい。脱硫フラックスは、最も安価で一般的な生石灰や石灰石等のCaOを主成分とするフラックスで良い。ただし、溶鉄を取鍋に排出する際にスラグが混入し、脱硫精錬後のスラグ中SiO2が増大すると脱硫能が低下する。本発明者が行った実験から、脱硫精錬後SiO2濃度は10質量%以上となると、処理後のメタル中[S]<0.005質量%までの十分な脱硫が進行しないことが判明した。したがって、電気炉や溶融還元炉等の脱硫前精錬炉から脱硫精錬用の取鍋に出湯する際に、脱硫精錬後のスラグ中SiO2濃度が10質量%未満となるように脱硫前精錬炉からのスラグ混入量を抑制する必要がある。 The desulfurization method may be any of a mechanical stirring method after adding the flux from the top, a gas bottom blowing stirring method, or a powder flux injection method, but from the viewpoint of desulfurization efficiency, the mechanical stirring method or the injection method is desirable. The desulfurization flux may be the cheapest and general flux mainly composed of CaO such as quicklime and limestone. However, when the molten iron is discharged into the ladle, slag is mixed, and when SiO 2 in the slag after desulfurization refining increases, the desulfurization ability decreases. From experiments conducted by the present inventors, it has been found that when the SiO 2 concentration after desulfurization refining is 10% by mass or more, sufficient desulfurization up to [S] <0.005% by mass in the treated metal does not proceed. Therefore, when tapping from a pre-desulfurization refining furnace such as an electric furnace or a smelting reduction furnace to a ladle for desulfurization refining, from the pre-desulfurization refining furnace, the SiO 2 concentration in the slag after desulfurization refining is less than 10% by mass. It is necessary to suppress the amount of slag mixed.

上記の本発明方法によると、脱硫処理前の溶鉄中[S]濃度が最大0.04質量%までであれば、脱硫処理後溶鉄中[S]<0.005質量%を達成することが可能である。また、脱硫処理前の溶鉄中[S]が0.015質量%以上であると従来技術では脱硫に困難が生じ、さらに脱硫処理前の溶鉄中[S]が0.02質量%以上の場合、従来技術では著しく脱硫不足が起こると考えられる。従って、本発明の含クロム溶鉄の脱硫方法において、脱硫処理前のメタル中[S]は0.015〜0.04質量%とすると好ましい。0.02〜0.04質量%とすると本発明の脱硫効果がより顕著に享受できるので更に好ましい。   According to the above-described method of the present invention, if the [S] concentration in the molten iron before the desulfurization treatment is up to 0.04% by mass, it is possible to achieve [S] <0.005% by mass in the molten iron after the desulfurization treatment. It is. Further, when [S] in the molten iron before the desulfurization treatment is 0.015% by mass or more, it is difficult to desulfurize by the conventional technique, and further, when [S] in the molten iron before the desulfurization treatment is 0.02% by mass or more, In the prior art, it is considered that there is a significant shortage of desulfurization. Therefore, in the method for desulfurizing chromium-containing molten iron of the present invention, [S] in the metal before desulfurization treatment is preferably 0.015 to 0.04 mass%. The amount of 0.02 to 0.04% by mass is more preferable because the desulfurization effect of the present invention can be enjoyed more remarkably.

脱硫前精錬炉で溶鉄中クロム濃度10〜50質量%の溶鉄を溶製するに際し、クロム源としてFe−Crを用いる。本発明においては、上記のように脱硫前の溶鉄中[S]濃度0.015質量%以上、あるいは0.02質量%以上と高くても、脱硫後溶鉄中[S]濃度を0.005%未満とすることが可能である。従って、クロム源としてSを多く含むFe−Crを用いることが可能である。本発明においては、Fe−CrのS含有量が0.01質量%以上0.06質量%以下のものを用いることが可能となる。一般に含有するS量が多いほどFe−Crは安価となる。安価Fe−Crを用いることによる経済効果享受を目的とする場合、Fe−CrのS含有量が0.02質量%以上0.06質量%以下のものが好ましく、0.03質量%以上0.06質量%以下のものが更に好ましい。   When melting molten iron having a chromium concentration of 10 to 50% by mass in molten iron in a smelting furnace before desulfurization, Fe—Cr is used as a chromium source. In the present invention, as described above, the [S] concentration in the molten iron before desulfurization is 0.015% by mass or more, or even if it is as high as 0.02% by mass or more, the [S] concentration in the molten iron after desulfurization is 0.005%. Can be less. Therefore, Fe—Cr containing a large amount of S can be used as a chromium source. In the present invention, it is possible to use a Fe-Cr S content of 0.01 mass% or more and 0.06 mass% or less. In general, the larger the amount of S contained, the cheaper the Fe—Cr. When the objective is to enjoy the economic effect by using inexpensive Fe—Cr, it is preferable that the S content of Fe—Cr is 0.02 mass% or more and 0.06 mass% or less, and 0.03 mass% or more and 0.0. More preferred is 06% by mass or less.

脱硫処理時間短縮の観点から、脱硫効率をさらに高めるためには、脱硫フラックスの融点を低下させる必要がある。本発明においては、Fの溶出規制からスラグの資源化に問題のある蛍石等の含CaF2物質は使用せず、生石灰や石灰石等のCaOを含むフラックスと、Al灰等のAl23を含む、もしくは添加後に酸化されてAl23となるフラックスを適当な割合で混合させ、融点が低下する組成としたフラックスを使用する。 In order to further improve the desulfurization efficiency from the viewpoint of shortening the desulfurization treatment time, it is necessary to lower the melting point of the desulfurization flux. In the present invention, a CaF 2 substance such as fluorite, which has a problem in recycling slag due to the elution regulation of F, is not used, but a flux containing CaO such as quicklime and limestone, and Al 2 O 3 such as Al ash. Or a flux that is oxidized after the addition to become Al 2 O 3 is mixed at an appropriate ratio to have a composition that lowers the melting point.

本発明ではさらに、融点を低下させることにより、脱硫処理中にスラグ中の酸化クロムの還元を促進できることを見出した。   In the present invention, it was further found that reduction of chromium oxide in slag can be promoted during the desulfurization treatment by lowering the melting point.

本発明者らは、種々の含クロム溶鉄の脱硫実験から、以下のことを知見した。まず、フラックス中のCaO濃度が高すぎると、フラックスのCaO活量は高いために脱硫能自体は高いものの、融点が上昇し、液相がほとんど無い固相状態のスラグとなり脱硫速度が低い。その上、脱硫精錬中に大気の巻き込みにより酸化したクロムの還元が進行せず、処理後のスラグ中クロム濃度が3質量%以上となり、クロムの歩留ロスになるとともにクロム溶出規制からスラグの資源化が困難となる。フラックス中のAl23濃度を増加させていくと、融点の低下により脱硫処理中のフラックス(スラグ)液相率が増加して脱硫速度が増加するが、液相率の低い領域では依然酸化クロムの還元の進行が遅く、処理後のスラグ中クロム濃度は高いままとなる。さらにフラックス中のAl23濃度を増加させ、スラグを高液相率の状態にすると、スラグ中のクロム酸化物と溶鉄中の炭素との反応が促進され、処理後のスラグ中クロム濃度は十分低下するようになる。ただし、Al23濃度を増加させすぎると、CaO活量の低下から脱硫効率が低下する。CaO/Al23濃度比率を適正な状態にした場合にのみ、短時間処理でのメタル中[S]<0.005質量%までの十分な脱硫と、処理後のスラグの資源化が容易な3質量%未満のスラグ中クロム濃度の達成が両立できることが判明した。特に、液相率が100%、すなわち完全液相のスラグ状態にした場合には、処理後のスラグ中クロム濃度は1質量%未満となり、普通鋼スラグと同等にスラグを資源化可能であることもわかった。なお、本発明者らによる含クロム鋼の脱硫実験では、液相率約60%〜100%の範囲で脱硫効率が最大となることも明らかとなった。 The present inventors have found the following from desulfurization experiments of various chromium-containing molten irons. First, if the CaO concentration in the flux is too high, the CaO activity of the flux is high, so the desulfurization ability itself is high, but the melting point rises, and the slag becomes a solid phase with almost no liquid phase, and the desulfurization rate is low. In addition, the reduction of chromium oxidized due to air entrainment during desulfurization and refining does not proceed, and the chromium concentration in the slag after treatment becomes 3% by mass or more, resulting in a loss of chromium yield and slag resources due to chromium elution regulations. It becomes difficult. Increasing the Al 2 O 3 concentration in the flux increases the flux (slag) liquid phase ratio during the desulfurization process due to the lowering of the melting point, increasing the desulfurization rate, but it is still oxidized in the region where the liquid phase ratio is low. The progress of chromium reduction is slow, and the chromium concentration in the slag after treatment remains high. If the Al 2 O 3 concentration in the flux is further increased and the slag is brought to a high liquid phase rate, the reaction between the chromium oxide in the slag and the carbon in the molten iron is promoted, and the chromium concentration in the slag after treatment is It will drop sufficiently. However, if the Al 2 O 3 concentration is increased too much, the desulfurization efficiency decreases due to the decrease in the CaO activity. Only when the CaO / Al 2 O 3 concentration ratio is in an appropriate state, sufficient desulfurization up to [S] <0.005% by mass in the metal in a short time treatment and easy recycling of slag after treatment It has been found that achieving a chromium concentration in the slag of less than 3% by mass is compatible. In particular, when the liquid phase ratio is 100%, that is, when the slag is in a completely liquid phase, the chromium concentration in the slag after processing is less than 1% by mass, and slag can be recycled as ordinary steel slag. I understand. In addition, in the desulfurization experiment of chromium-containing steel by the present inventors, it became clear that the desulfurization efficiency becomes maximum in the range of the liquid phase ratio of about 60% to 100%.

種々の脱硫実験から、上記の適正なCaO/Al23濃度比率を各精錬前温度で調査した結果、図2のCaO−Al23二元系状態図上に太線で示した範囲で、処理後のメタル中[S]<0.005質量%までの十分な脱硫と、処理後のスラグの資源化が容易な3質量%未満のスラグ中クロム濃度の達成が両立できることが明らかとなった。この範囲を定式化すると、下記のように脱硫精錬前温度T(℃)の関数として表される。
−0.000375T+0.91≦AL/(CA+AL)≦−0.000375T+1.06 (2)
ここで、CA:フラックス中のCaO濃度(質量%)、AL:フラックス中のAl23濃度(質量%)である。なお、液相率が100%となり、かつCaOの活量が最も高くスラグの脱硫能が高い、状態図の液相線上の組成が、脱硫効率と処理後のスラグ資源化の点で最も望ましいフラックス組成である。
From various desulfurization experiments, the above-mentioned appropriate CaO / Al 2 O 3 concentration ratio was investigated at each pre-refining temperature. As a result, in the range indicated by the thick line on the CaO-Al 2 O 3 binary phase diagram of FIG. It is clear that sufficient desulfurization up to [S] <0.005% by mass in the treated metal and achievement of chromium concentration in the slag of less than 3% by mass, which makes it easy to recycle the treated slag, can be achieved. It was. When this range is formulated, it is expressed as a function of the temperature T (° C.) before desulfurization and refining as follows.
−0.000375T + 0.91 ≦ AL / (CA + AL) ≦ −0.000375T + 1.06 (2)
Here, CA: CaO concentration (mass%) in the flux, AL: Al 2 O 3 concentration (mass%) in the flux. The liquid phase ratio is 100%, the activity of CaO is the highest, and the desulfurization ability of slag is the highest. The composition on the phase line of the phase diagram is the most desirable flux in terms of desulfurization efficiency and slag resources after treatment. Composition.

脱硫速度の増加とクロム酸化物の還元の両方を得ることのできる液相率が実現するには、溶鉄温度が低いほど、Al23含有量を高くする必要がある。(2)式の左辺については、脱硫速度の増加とクロム酸化物の還元の両方を得ることのできる液相率が実現できる境界線を示している。温度が1400℃未満では液相が存在し得ない条件となるため、本範囲のフラックス組成を使用する場合の脱硫精錬前温度の下限は1400℃となる。 In order to realize a liquid phase ratio capable of obtaining both an increase in desulfurization rate and reduction of chromium oxide, it is necessary to increase the Al 2 O 3 content as the molten iron temperature decreases. About the left side of (2) Formula, the boundary line which can implement | achieve the liquid phase rate which can obtain both the increase in a desulfurization rate and reduction | restoration of chromium oxide is shown. If the temperature is less than 1400 ° C., the liquid phase cannot be present. Therefore, the lower limit of the temperature before desulfurization refining when using the flux composition in this range is 1400 ° C.

フラックス中のAl23濃度が高くなりすぎると、フラックスのCaO活量が低下して脱硫速度が低下する。CaO−Al23系2元状態図(図2)のAl23濃度50%以下の液相領域において、CaOの等活量線図は、ほぼ液相線と同じ勾配を有している。図2において太線で示す平行四辺形の右辺、即ち(2)式右辺は、CaOの等活量線図であって、脱硫能力を十分に保持する境界線を意味している。従って、(2)式の右辺は、脱硫能力を発揮することのできる限界濃度を示している。 If the Al 2 O 3 concentration in the flux becomes too high, the CaO activity of the flux decreases and the desulfurization rate decreases. In the CaO-Al 2 O 3 binary phase diagram (FIG. 2) in the liquid phase region where the Al 2 O 3 concentration is 50% or less, the CaO isoactivity diagram has almost the same gradient as the liquid phase line. Yes. The right side of the parallelogram shown by a thick line in FIG. 2, that is, the right side of the formula (2) is an isoactivity diagram of CaO, and means a boundary line that sufficiently maintains the desulfurization capacity. Therefore, the right side of the formula (2) indicates the limit concentration at which the desulfurization ability can be exhibited.

しかしながら、脱硫フラックスを上述の適正な範囲の組成に配合した場合でも、溶鉄を取鍋に排出する際にスラグが混入し、脱硫精錬後のスラグ中SiO2が増大すると脱硫能が低下する。本発明者が行った実験から、脱硫精錬後SiO2濃度は10質量%以上となると、処理後のメタル中[S]<0.005質量%までの十分な脱硫が進行しないことが判明した。 However, even when the desulfurization flux is blended in the above-mentioned proper range of composition, slag is mixed when the molten iron is discharged into the ladle, and the desulfurization ability decreases when SiO 2 in the slag after desulfurization refining increases. From experiments conducted by the present inventors, it has been found that when the SiO 2 concentration after desulfurization refining is 10% by mass or more, sufficient desulfurization up to [S] <0.005% by mass in the treated metal does not proceed.

なお、フラックス中のCaOとAl23の含有割合が(2)式の左辺に近くスラグ中に固相がある程度存在する場合には、攪拌用のインペラーや粉体吹き込み用の浸漬ノズルあるいは取鍋の耐火物にMgOを含むものを使用した場合でも耐火物溶損量は少ないが、フラックス中のAl23の含有比率を高め、フラックスを低融点組成とすることで、スラグを完全液相に近い状態にした場合は、上述のとおり、スラグのMgO飽和溶解度が高いために耐火物の溶損が大きく、耐火物コストの増大を招く。この場合でも、予めフラックスに5質量%以上のMgOを配合することで耐火物の溶損を抑制できることが判明した。但し、20質量%超のMgOを配合すると、スラグの液相率が低下しすぎて、脱硫効率の低下と処理後のスラグ中クロム濃度が増加するため、MgOの配合比率の上限は20質量%とするのが望ましい。 If the CaO and Al 2 O 3 content in the flux is close to the left side of equation (2) and a solid phase is present in the slag to some extent, an impeller for stirring, an immersion nozzle for blowing powder, Even when the pan refractory contains MgO, the amount of refractory melt is small, but the content ratio of Al 2 O 3 in the flux is increased, and the flux has a low melting point composition, so that the slag can be completely liquidized. When it is in a state close to the phase, as described above, the slag has a high MgO saturation solubility, so that the refractory has a large melting loss, resulting in an increase in the refractory cost. Even in this case, it has been found that melting of the refractory can be suppressed by previously blending 5% by mass or more of MgO with the flux. However, when more than 20% by mass of MgO is blended, the liquid phase ratio of the slag decreases too much, and the desulfurization efficiency decreases and the chromium concentration in the slag after treatment increases, so the upper limit of the MgO blending ratio is 20% by mass. Is desirable.

脱硫フラックス中には、CaO、Al23、MgO以外の成分を含有することもできるが、これら3成分以外の成分含有量を10質量%以下とする。即ち、上記(3)式を満たすことが必要である。これにより、上記本発明の効果を十分に発揮することができる。 Components other than CaO, Al 2 O 3 , and MgO can be contained in the desulfurization flux, but the content of components other than these three components is 10% by mass or less. That is, it is necessary to satisfy the above expression (3). Thereby, the effect of the said invention can fully be exhibited.

Al23を含有してCaOとAl23の比率を適正な範囲とすれば、上記のように脱硫効率向上による短時間での脱硫処理とスラグ中クロムの還元速度向上によるスラグ資源化の効果を発揮することができるが、本発明のフラックスはAl23を積極的に含有しない場合をも含む。また、MgOを含有すれば上記のように耐火物溶損を低減する効果を発揮することができるが、本発明の脱硫フラックスはMgOを積極的に添加しない場合をも含む。 If Al 2 O 3 the appropriate range of the ratio of CaO and Al 2 O 3 contained, slag recycling by reduction speedup desulfurization and slag in the chromium in a short time by the desulfurization efficiency, as described above However, the flux of the present invention includes a case where Al 2 O 3 is not actively contained. Further, if MgO is contained, the effect of reducing the refractory melting loss can be exhibited as described above. However, the desulfurization flux of the present invention includes a case where MgO is not actively added.

本発明の脱硫フラックスはまた、蛍石等のF(フッ素)源を実質的に添加しないことを特徴としている。実質的に添加しないこととは、前記フラックスを用いた脱硫精錬後のスラグからフッ素の溶出が顕著には認められないことを指すもので、本発明者らの知見ではフラックス組成においてFが1質量%以下となる場合を指す。Fが0.5質量%以下であれば更に好ましい。   The desulfurization flux of the present invention is also characterized in that substantially no F (fluorine) source such as fluorite is added. The fact that it is not substantially added means that elution of fluorine is not remarkably recognized from the slag after desulfurization and refining using the flux. According to the knowledge of the present inventors, F is 1 mass in the flux composition. % Or less. More preferably, F is 0.5% by mass or less.

(実施例1)
1トンの溶鉄を溶解できる試験溶解炉2基を用いて、以下に示す実機溶銑鍋での脱硫処理の7分の1相似モデルでの脱硫試験を行った。片方の試験溶解炉で所定成分の含クロム溶鉄を溶解した後、もう1基の溶解炉に溶鉄を移し替え、フラックスの上方からの一括添加後、インペラーを用いた機械式攪拌での脱硫処理を施した。
Example 1
Using two test melting furnaces capable of melting 1 ton of molten iron, a desulfurization test was conducted with a 1/7 similarity model of the desulfurization treatment in an actual hot metal ladle shown below. After melting the chromium-containing molten iron of the specified component in one of the test melting furnaces, transfer the molten iron to the other melting furnace, add it from the top of the flux, and then desulfurize it with mechanical stirring using an impeller. gave.

実機溶銑鍋の脱硫処理における機械攪拌では、溶銑鍋に収容した330トンの溶銑に対し、羽根の直径1415mm、長さ855mmである4枚羽根構成の耐火物でコーティングした攪拌用インペラーを用いて機械攪拌を行う。回転軸の直径は600mmである。このとき用いる攪拌用インペラーにおいては、上部根元半径を300mm、下部根元半径を600mm、角度θを14度とし、膨出部は用いていない。また、攪拌時の溶銑湯面凹部深さに対するインペラー上端深さの比が0.7となるように、インペラーの回転数と浸漬深さが調整されている。
実施例における1トンの試験溶解炉を用いた脱硫試験では、上記実機での脱硫処理と全く相似の形状であり、サイズが7分の1である溶解炉内るつぼ、攪拌用インペラーを用いた。攪拌用インペラーのコーティング耐火物にはMgO系のものを使用した。また、攪拌用インペラーの回転数、浸漬深さについては、攪拌時の溶鉄湯面凹部深さに対するインペラー上端深さの比が0.7となるように調整した。
In the mechanical stirring in the desulfurization treatment of the actual hot metal ladle, a machine using a stirring impeller coated with a refractory having a four-blade configuration with a blade diameter of 1415 mm and a length of 855 mm for 330 tons of hot metal contained in the hot metal ladle. Stir. The diameter of the rotating shaft is 600 mm. In the stirring impeller used at this time, the upper root radius is 300 mm, the lower root radius is 600 mm, the angle θ is 14 degrees, and the bulging portion is not used. Moreover, the rotation speed and immersion depth of the impeller are adjusted so that the ratio of the impeller upper end depth to the hot metal surface recess depth during stirring is 0.7.
In the desulfurization test using the 1-ton test melting furnace in the examples, a melting furnace crucible and a stirring impeller having a shape that is completely similar to the desulfurization treatment in the above-mentioned actual machine and having a size of 1/7 were used. As the coating refractory for the impeller for stirring, an MgO-based one was used. Moreover, about the rotation speed and immersion depth of the impeller for stirring, it adjusted so that ratio of the impeller upper end depth with respect to the molten iron surface recessed part depth at the time of stirring might be 0.7.

溶鉄を脱硫処理用の溶解炉に移し替えた後、フラックスの原料としては、平均直径100μmのCaO粉とAl23粉および一部の試験ではMgO粉を使用し、予めミキサーにて物理的に混合したものを脱硫フラックスとして使用した。脱硫フラックスの使用量は全て7kgとし、フラックス添加直後にインペラーによる攪拌を開始した。インペラー攪拌による脱硫精錬時間は20分とし、精錬時間を15分に短縮した試験も実施した。脱硫処理前溶鉄の[S]濃度は0.015〜0.04質量%に調整し、精錬後の[S]濃度が0.005質量%未満となったものを良好な脱硫と判断した。また、脱硫精錬後のスラグ中全Cr濃度(T.Cr)が5質量%未満となったものをスラグ資源化性良好と判断した。 After the molten iron is transferred to the melting furnace for desulfurization treatment, the raw material for the flux is CaO powder with an average diameter of 100 μm and Al 2 O 3 powder, and in some tests, MgO powder is used. The mixture was used as a desulfurization flux. The amount of desulfurization flux used was 7 kg, and stirring by the impeller was started immediately after the addition of the flux. A test was also conducted in which the desulfurization refining time by impeller stirring was 20 minutes and the refining time was reduced to 15 minutes. The [S] concentration of the molten iron before desulfurization was adjusted to 0.015 to 0.04% by mass, and the [S] concentration after refining was less than 0.005% by mass was judged as good desulfurization. Moreover, what the total Cr density | concentration (T.Cr) in slag after desulfurization refining became less than 5 mass% was judged that slag resource property is favorable.

表1には、脱硫精錬開始前の含クロム溶鉄の組成および精錬後の溶鉄組成、脱硫精錬開始前および精錬後の溶鉄温度、添加したフラックスの配合組成および脱硫精錬後のスラグ組成、インペラー耐火物の溶損による半径減少量を示した。   Table 1 shows the composition of chromium-containing molten iron before the start of desulfurization refining and the molten iron composition after refining, the temperature of molten iron before and after the start of desulfurization refining, the composition of the added flux, the slag composition after desulfurization refining, and the impeller refractory The amount of radius reduction due to melting damage was shown.

表1において、No.1からNo.16が本発明の方法によって安定した高脱硫能を得ることができた実施例である。脱硫精錬前温度と溶鉄中炭素濃度およびクロム濃度を(1)式で規定する適正な範囲内に調整し、脱硫処理後のスラグ中SiO2濃度を10質量%未満にすることで、精錬後[S]濃度0.005質量%未満までの安定した脱硫が可能となっている。また、No.17からNo.37は、本発明の方法によって、安定した高脱硫能を得ると同時に、脱硫処理後のスラグ中Cr濃度が低く、資源化に適したスラグにすることができた実施例である。特に、No.20からNo.37については、フラックス中のCaOとAl23の含有割合を適正な範囲に制御することにより、15分という短時間での脱硫精錬にも関わらず、精錬後[S]濃度0.005質量%未満までの安定した脱硫が可能となっている。 In Table 1, no. 1 to No. No. 16 is an example in which stable high desulfurization ability could be obtained by the method of the present invention. By adjusting the temperature before desulfurization refining, the concentration of carbon in molten iron and the concentration of chromium within the appropriate ranges specified by Equation (1), and reducing the SiO 2 concentration in the slag after desulfurization to less than 10% by mass, S] Stable desulfurization up to a concentration of less than 0.005 mass% is possible. No. 17 to No. 37 is an example in which a stable high desulfurization ability was obtained by the method of the present invention, and at the same time, the Cr concentration in the slag after the desulfurization treatment was low, and a slag suitable for resource recycling could be obtained. In particular, no. 20 to No. For No. 37, by controlling the content ratio of CaO and Al 2 O 3 in the flux to an appropriate range, the [S] concentration after refining is 0.005 mass despite the desulfurization refining in a short time of 15 minutes. Stable desulfurization up to less than% is possible.

フラックス中のCaOとAl23の含有割合が(2)式の左辺に近くスラグ中に固相がある程度存在する場合には、インペラーの耐火物溶損量も低い。フラックス中のAl23の含有比率が高くなり、スラグが完全液相に近い状態になった場合には、インペラー耐火物の溶損量が多くなるが、この場合でも、MgO粉を添加してスラグ中MgO含有量を5%以上とすることで、耐火物の溶損抑制も可能となっている。溶鉄の脱硫精錬前温度、炭素濃度、クロム濃度および適正組成のフラックス添加を行い、溶解用溶解炉からのスラグの混入によるSiO2濃度増加を10質量%未満に抑えることで、短時間処理においても精錬後[S]濃度0.005質量%未満までの安定した脱硫と、スラグ資源化が容易なT.Cr5質量%未満へのスラグ組成制御の両立が可能となっていることがわかる。 When the content ratio of CaO and Al 2 O 3 in the flux is close to the left side of the formula (2) and a solid phase is present in the slag to some extent, the refractory erosion amount of the impeller is also low. When the content ratio of Al 2 O 3 in the flux becomes high and the slag is in a state close to a complete liquid phase, the amount of impregnated refractory is increased, but even in this case, MgO powder is added. By making the MgO content in the slag 5% or more, the refractory can be prevented from being damaged. Addition of flux of molten iron before desulfurization refining temperature, carbon concentration, chromium concentration and proper composition, and suppressing increase in SiO 2 concentration due to mixing of slag from melting melting furnace to less than 10% by mass, even in short time processing After refining [S] concentration of less than 0.005 mass%, stable desulfurization and slag resources can be easily used. It turns out that coexistence of slag composition control to less than 5 mass% of Cr is possible.

フラックス組成が同程度のもの同士を比較したとき、溶鉄温度が低いほどインペラー耐火物溶損量も少なくなっている。溶鉄温度が1500℃未満であると好ましい結果を得ることができる。   When the flux compositions having the same degree are compared, the lower the molten iron temperature, the smaller the impeller refractory erosion amount. A preferable result can be obtained when the molten iron temperature is less than 1500 ° C.

一方、No.38からNo.61が比較例の結果を示す。脱硫精錬前温度と溶鉄中炭素濃度およびクロム濃度が適正な範囲から外れる場合には、脱硫能が悪化して20分という長時間精錬にも関わらず目標の[S]濃度まで到達しないことがわかる。また、No.41、43、48、54、59のように、溶解用の炉からの移し替えの際にスラグの混入量が多く、スラグ中SiO2濃度が10質量%を超えた場合は、脱硫精錬前温度と溶鉄中炭素濃度およびクロム濃度が適正な範囲であっても、脱硫能が悪化して目標の[S]濃度まで到達しないことがわかる。 On the other hand, no. 38 to No. 61 shows the result of the comparative example. When the temperature before desulfurization refining, the concentration of carbon in molten iron, and the concentration of chromium deviate from the proper ranges, the desulfurization ability deteriorates and the target [S] concentration is not reached despite refining for a long time of 20 minutes. . No. When the amount of slag mixed is large and the SiO 2 concentration in the slag exceeds 10% by mass, such as 41, 43, 48, 54, 59, the temperature before desulfurization and refining It can be seen that even if the carbon concentration and chromium concentration in the molten iron are in the proper ranges, the desulfurization ability deteriorates and the target [S] concentration is not reached.

(実施例2)
実施例1と同じ試験溶解炉2基を用いて、粉体インジェクション方式での脱硫試験を行った。片方の試験溶解炉で所定成分の含クロム溶鉄を溶解した後、もう1基の溶解炉に溶鉄を移し替え、浸漬ノズルを用いてフラックスを吹き込みつつ、脱硫処理を施した。
(Example 2)
Using the same two test melting furnaces as in Example 1, a desulfurization test by a powder injection method was performed. After melting the chromium-containing molten iron of a predetermined component in one test melting furnace, the molten iron was transferred to another melting furnace, and desulfurization treatment was performed while blowing flux using an immersion nozzle.

浸漬ノズルは、先端に直径10mmの開口部を水平方向に2つ有するものを用い、MgO系耐火物でコーティングした。開口部が鉄浴の深さの底部から1/3となるように浸漬ノズルからの吹き込み位置を調整し、Arガス13L/minをキャリアガスとして470g/minのフラックス吹き込み速度で15分間インジェクション精錬を行った。1回の精錬処理におけるフラックス吹き込み量は、実施例1と同じ7kgである。使用した脱硫フラックスの種類、粒径、脱硫処理前溶鉄[S]濃度、脱硫特性と脱硫精錬後のスラグ資源化性の判定基準も全て実施例1と同様である。   An immersion nozzle having two openings with a diameter of 10 mm at the tip in the horizontal direction was coated with an MgO-based refractory. Adjust the injection position from the immersion nozzle so that the opening is 1/3 from the bottom of the depth of the iron bath, and perform injection refining for 15 minutes at a flux injection speed of 470 g / min using Ar gas 13 L / min as a carrier gas. went. The amount of flux blown in one refining process is 7 kg as in the first embodiment. The type of desulfurization flux used, the particle size, the concentration of molten iron [S] before desulfurization, the desulfurization characteristics, and the judgment criteria for the slag resourceability after desulfurization refining are all the same as in Example 1.

表2には、脱硫精錬開始前の含クロム溶鉄の組成および精錬後の溶鉄組成、脱硫精錬開始前および精錬後の溶鉄温度、添加したフラックスの配合組成および脱硫精錬後のスラグ組成、浸漬ノズルのコーティング耐火物の溶損によるノズル半径減少量を示した。   Table 2 shows the composition of the chrome-containing molten iron before the desulfurization refining and the molten iron composition after the refining, the molten iron temperature before and after the desulfurization refining, the composition of the added flux and the slag composition after the desulfurization refining, The amount of nozzle radius decrease due to melting of the coated refractory was shown.

表2において、No.62からNo.77が本発明の方法によって安定した高脱硫能を得ることができた実施例である。脱硫精錬前温度と溶鉄中炭素濃度およびクロム濃度を(1)式で規定する適正な範囲内に調整し、脱硫処理後のスラグ中SiO2濃度を10質量%未満にすることで、精錬後[S]濃度0.005質量%未満までの安定した脱硫が可能となっている。また、No.78からNo.98は、本発明の方法によって、安定した高脱硫能を得ると同時に、脱硫処理後のスラグ中Cr濃度が低く、資源化に適したスラグにすることができた実施例である。特に、No.81からNo.98については、フラックス中のCaOとAl23の含有割合を適正な範囲に制御することにより、15分という短時間での脱硫精錬にも関わらず、精錬後[S]濃度0.005質量%未満までの安定した脱硫が可能となっている。 In Table 2, no. 62 to No. No. 77 is an example in which stable high desulfurization ability could be obtained by the method of the present invention. By adjusting the temperature before desulfurization refining, the concentration of carbon in molten iron and the concentration of chromium within the appropriate ranges specified by Equation (1), and reducing the SiO 2 concentration in the slag after desulfurization to less than 10% by mass, S] Stable desulfurization up to a concentration of less than 0.005 mass% is possible. No. 78 to No. No. 98 is an example in which stable high desulfurization ability was obtained by the method of the present invention, and at the same time, the Cr concentration in the slag after the desulfurization treatment was low, and the slag was suitable for resource recycling. In particular, no. 81 to No. For 98, by controlling the content ratio of CaO and Al 2 O 3 in the flux to an appropriate range, the [S] concentration after refining is 0.005 mass in spite of desulfurization refining in a short time of 15 minutes. Stable desulfurization up to less than% is possible.

フラックス中のCaOとAl23の含有割合が(2)式の左辺に近くスラグ中に固相がある程度存在する場合には、ノズルの耐火物溶損量も低い。フラックス中のAl23の含有比率が高くなり、スラグが完全液相に近い状態になった場合には、浸漬ノズル耐火物の溶損量が多くなるが、この場合でも、MgO粉を添加してスラグ中MgO含有量を5%以上とすることで、耐火物の溶損抑制も可能となっている。溶鉄の脱硫精錬前温度、炭素濃度、クロム濃度および適正組成のフラックス添加を行い、溶解用溶解炉からのスラグの混入によるSiO2濃度増加を10質量%未満に抑えることで、短時間処理においても精錬後[S]濃度0.005質量%未満までの安定した脱硫と、スラグ資源化が容易なT.Cr5質量%未満へのスラグ組成制御の両立が可能となっていることがわかる。 When the content ratio of CaO and Al 2 O 3 in the flux is close to the left side of equation (2) and a solid phase is present in the slag to some extent, the refractory erosion amount of the nozzle is also low. When the content ratio of Al 2 O 3 in the flux is high and the slag is almost in the liquid phase, the amount of erosion of the immersion nozzle refractory increases, but in this case as well, MgO powder is added. And by making the MgO content in the slag 5% or more, the refractory can be prevented from being damaged. Addition of flux of molten iron before desulfurization refining temperature, carbon concentration, chromium concentration and proper composition, and suppressing increase in SiO 2 concentration due to mixing of slag from melting melting furnace to less than 10% by mass, even in short time processing After refining [S] concentration of less than 0.005 mass%, stable desulfurization and slag resources can be easily used. It turns out that coexistence of slag composition control to less than 5 mass% of Cr is possible.

フラックス組成が同程度のもの同士を比較したとき、溶鉄温度が低いほどノズル耐火物溶損量も少なくなっている。溶鉄温度が1500℃未満であると好ましい結果を得ることができる。   When the flux compositions having the same degree are compared with each other, the lower the molten iron temperature, the smaller the amount of nozzle refractory melted. A preferable result can be obtained when the molten iron temperature is less than 1500 ° C.

一方、No.99からNo.122が比較例の結果を示す。脱硫精錬前温度と溶鉄中炭素濃度およびクロム濃度が適正な範囲から外れる場合には、脱硫能が悪化して20分という長時間精錬にも関わらず目標の[S]濃度まで到達しないことがわかる。また、No.102、104、109、115、120のように、溶解用の炉からの移し替えの際にスラグの混入量が多く、スラグ中SiO2濃度が10質量%を超えた場合は、脱硫精錬前温度と溶鉄中炭素濃度およびクロム濃度が適正な範囲であっても、脱硫能が悪化して目標の[S]濃度まで到達しないことがわかる。 On the other hand, no. 99 to No. 122 shows the result of the comparative example. When the temperature before desulfurization refining, the concentration of carbon in molten iron, and the concentration of chromium deviate from the proper ranges, the desulfurization ability deteriorates and the target [S] concentration is not reached despite refining for a long time of 20 minutes. . No. When the amount of slag mixed is large during transfer from the melting furnace, such as 102, 104, 109, 115, 120, and the SiO 2 concentration in the slag exceeds 10 mass%, the temperature before desulfurization refining It can be seen that even if the carbon concentration and chromium concentration in the molten iron are in the proper ranges, the desulfurization ability deteriorates and the target [S] concentration is not reached.

溶鉄中クロム濃度に応じた炭素濃度と脱硫精錬前温度の適正な範囲を示す図である。It is a figure which shows the appropriate range of the carbon concentration according to chromium concentration in molten iron, and the temperature before desulfurization refining. 脱硫フラックス中のCaOとAl23の適正な比率の範囲を示す図である。Is a diagram showing the range of the proper ratio of CaO and Al 2 O 3 in the desulfurization flux.

Claims (5)

クロムを10質量%以上50質量%以下含有し、炭素を2.5質量%以上10質量%以下含有する含クロム溶鉄を脱硫精錬前温度1250℃以上1700℃以下で脱硫精錬するに際し、脱硫前精錬炉で、出湯後の脱硫精錬前温度T(℃)と溶鉄中クロム濃度CR(質量%)に対して(1)式を満足するように溶鉄中炭素濃度C(質量%)を調整する第1の工程と、脱硫精錬後のスラグ中SiO2濃度が10質量%未満となるように脱硫前精錬炉からのスラグ混入量を抑制して取鍋に出湯する第2の工程と、F濃度が1質量%以下の脱硫フラックスを使用して取鍋内で脱硫精錬する第3の工程を有することを特徴とする、含クロム溶鉄の脱硫方法。
C≧0.11×CR+15000/(T+273)−6.16 (1)
When desulfurizing and refining chromium-containing molten iron containing 10% to 50% by weight of chromium and 2.5% to 10% by weight of carbon at a pre-desulfurization temperature of 1250 ° C to 1700 ° C, refining before desulfurization The first is to adjust the carbon concentration C (mass%) in molten iron so as to satisfy the formula (1) with respect to the temperature T (° C) before desulfurization and refining after hot water and the chromium concentration CR (mass%) in molten iron. The second step of discharging the hot water into the ladle while suppressing the amount of slag mixed from the smelting furnace before desulfurization so that the SiO 2 concentration in the slag after desulfurization refining is less than 10% by mass, and the F concentration is 1. A desulfurization method for molten iron containing chromium, comprising a third step of desulfurization and refining in a ladle using a desulfurization flux of less than mass%.
C ≧ 0.11 × CR + 15000 / (T + 273) −6.16 (1)
脱硫精錬前温度T(℃)が1400℃以上であり、脱硫フラックスのCaO濃度(質量%)(以下「CA」ともいう。)とAl23濃度(質量%)(以下「AL」ともいう。)、およびMgO濃度(質量%)(以下「MG」ともいう。)とTとの関係が下記(2)〜(3)式を満たすことを特徴とする、請求項1記載の含クロム溶鉄の脱硫方法。
−0.000375T+0.91≦AL/(CA+AL)≦−0.000375T+1.06 (2)
CA+AL+MG≧90 (3)
The temperature T (° C.) before desulfurization refining is 1400 ° C. or higher, and the CaO concentration (mass%) (hereinafter also referred to as “CA”) and Al 2 O 3 concentration (mass%) (hereinafter also referred to as “AL”) of the desulfurization flux. ) And MgO concentration (mass%) (hereinafter also referred to as “MG”) and T satisfy the following formulas (2) to (3): Desulfurization method.
−0.000375T + 0.91 ≦ AL / (CA + AL) ≦ −0.000375T + 1.06 (2)
CA + AL + MG ≧ 90 (3)
MgOを5質量%以上20質量%以下含有する脱硫フラックスを使用することを特徴とする、請求項2記載の含クロム溶鉄の脱硫方法。   The desulfurization flux containing MgO in an amount of 5% by mass or more and 20% by mass or less is used. 脱硫フラックスを使用して取鍋内で脱硫精錬するに際し、取鍋内の溶鉄を攪拌することを特徴とする請求項1乃至3のいずれかに記載の含クロム溶鉄の脱硫方法。   The method for desulfurization of molten iron containing chromium according to any one of claims 1 to 3, wherein the molten iron in the ladle is stirred when desulfurizing and refining in the ladle using the desulfurization flux. 含クロム溶鉄中のクロム源としてFe−Crを用いることを特徴とする請求項1乃至4のいずれかに記載の含クロム溶鉄の脱硫方法。   The method for desulfurization of chrome-containing molten iron according to any one of claims 1 to 4, wherein Fe-Cr is used as a chromium source in the chrome-containing molten iron.
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