JP5266903B2 - Method for producing Mn alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce Mn and an Mn alloy containing 0.03 mass% or less phosphorus and preferably 0.02 mass% or less phosphorus, by effectively dephosphorizing the Mn and the Mn alloy with an inexpensive method which is suitable for mass production. <P>SOLUTION: This production method includes dephosphorizing a molten Mn or Mn alloy containing 2.0 mass% or less carbon, 0.5 mass% or less oxygen and 60 mass% or more Mn at a molten metal temperature of 1,350 to 1,500&deg;C, by using a flux which contains 80 mass% or more in total of CaF<SB>2</SB>and CaC<SB>2</SB>and also has a mass ratio thereof in a range satisfying the expression of (CaC<SB>2</SB>)/ä(CaC<SB>2</SB>)+(CaF<SB>2</SB>)}&times;100=30 to 65%. It is preferable to add at least one metal Ca source selected from metal Ca and a Ca alloy to the flux. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for producing Mn and a Mn alloy having a reduced phosphorus content, which is a main impurity of Mn and a Mn alloy.

  Mn and Mn alloys are mostly used as Mn sources necessary for steel production. Examples of Mn alloys include Mn-Fe alloys called ferromanganese (or manganese alloy iron), Mn-Si alloys called silicomanganese, and more than conventional standards derived from manganese alloy iron. Examples thereof include manganese alloy iron having a high Mn concentration. In the present specification, the “Mn alloy” means a Mn-based alloy, that is, an alloy in which Mn is a main alloy element.

  Mn and an Mn alloy are mainly produced by a method in which manganese ore is reduced by hot carbon in the melting temperature range of the alloy, or a method in which manganese ore or manganese-containing slag is reduced by silicon. Therefore, the produced Mn and the Mn alloy inevitably contain a high concentration of carbon derived from carbon reduction or silicon derived from silicon reduction, and phosphorus accompanying ores and auxiliary materials. In recent years, there has been a strong demand for the use of raw materials such as lower-grade manganese ore, and it is thought that the increase in phosphorus concentration will greatly hinder the use of such raw materials.

  When such Mn or Mn alloy is used as a Mn source for steel production, carbon or silicon and phosphorus contained therein are also introduced into the steel. Of these, carbon and silicon are components that are permissible in a considerable amount for steel, so if the amount of addition is determined according to the amount of the permissible component, the addition of Mn source to the steel does not pose a problem. On the other hand, phosphorus often has an adverse effect on the quality of steel, which is the final product, and many high-grade steels manufactured in recent years are impurity elements whose content is generally strictly limited. Therefore, if the phosphorus in the molten steel increased by the Mn concentration adjustment performed by adding Mn or Mn alloy to the molten steel exceeds the allowable limit, it is necessary to remove the phosphorus from the molten steel after the Mn concentration adjustment. There is.

  However, the Mn concentration is often adjusted just before casting, which is the final stage of the steelmaking process, and in that case, it is virtually impossible to remove phosphorus from the molten steel. Therefore, in this case, it is essential to adjust the Mn concentration of the molten steel using Mn or Mn alloy having a low phosphorus content. As described above, Mn and Mn alloys having a high phosphorus content may be inappropriate for use in the production of steel such as high-grade steel, and Mn and Mn alloys having a sufficiently low phosphorus content that can be used in such cases. Is required.

  As high-purity Mn, there is electrolytic manganese produced by dissolving manganese ore in an aqueous sulfuric acid solution and then electrolyzing the obtained aqueous manganese sulfate solution to obtain metallic manganese. Although electrolytic manganese has a very high purity with a phosphorus content of about 10 ppm, it is very expensive and its supply is limited. Electrolytic manganese is expensive because Mn is a relatively base metal, resulting in poor current efficiency in electrolysis, high electrical energy costs, and a large amount of sulfuric acid waste treatment costs and environmental measures costs. There is a cause in the bulk. Therefore, manufacturing Mn and Mn alloys having a low phosphorus content without using electrolysis has a very high industrial value.

  As a method capable of realizing industrial mass production of Mn and Mn alloys having a low phosphorus content, there is a method of selectively removing phosphorus (ie, dephosphorization) to a low concentration using a high temperature chemical reaction. Since Mn and phosphorus in Mn alloys are chemically stable, it has been difficult to realize. In the prior art, a technique for solving this difficulty has been studied.

  As a dephosphorization method from molten iron using a high temperature chemical reaction, there is a so-called oxidative dephosphorization method in which molten iron is oxidized and phosphorus is absorbed by basic slag. Japanese Patent Publication No. 5-80541 (Patent Document 1) discloses a method in which this method is applied to a Mn alloy, and a high manganese iron alloy is oxidized and dephosphorized using slag composed mainly of barium oxide having the highest basicity. Is disclosed. However, this method uses a barium compound such as barium oxide, which is expensive and limited in terms of resources, and has a minimum phosphorus concentration of 0.04% by mass and a high dephosphorization rate of 67%. It was ˜68%, and since the dephosphorization limit was particularly low, it was difficult to say that it was practical.

As a method contrasted with oxidative dephosphorization, there is a reductive dephosphorization method. In this method, Ca, which is an element that forms stable saponified substances even at high temperatures, is used to cause the following reaction:
3Ca + 2P = Ca ₃ P ₂ (s) (1)
At this time, since Ca is an active metal having a relatively low melting point and high reactivity, its supply method becomes a problem.

A solution to deal with this problem is presented in Japanese Patent Publication No. 60-11099 (Patent Document 2). In Patent Document 2, a manganese alloy iron having a Mn content of 60% or more, a Si content (X%) and a C content (Y%) satisfying 0.27X + Y ≦ 4.2 is prepared. Dephosphorization by adding a dephosphorizing agent containing CaC ₂ : 30 to 70% and CaF ₂ : 15 to 60% in an amount of 1 to 10% of the manganese alloy iron while melting iron in an Ar atmosphere. The manufacturing method of the low phosphorus manganese alloy iron which consists of this is disclosed.

  In the example of Patent Document 2, it is shown that manganese alloy iron having an ultimate phosphorus concentration of 0.022 to 0.067% (dephosphorization rate of 55 to 85%) was obtained by performing the above method. ing. However, in consideration of recent upgrades in steel products and higher efficiency in the steel process, the phosphorus concentration in manganese alloy iron is required to be as low as possible as that of electrolytic manganese. Is not enough.

In addition, by using CaC ₂ , there arises a problem of so-called carbon pickup in which carbon generated by decomposition of CaC ₂ is absorbed by manganese alloy iron. Therefore, when the amount of CaC ₂ used is increased, even if manganese alloy iron with a low carbon concentration (low carbon ferromanganese as defined in JIS) is used as a starting material, the increase in carbon concentration increases, and carbon with a high carbon concentration Only alloy iron can be produced. Furthermore, since the Si content (X) is limited, it cannot be applied to Si-containing Mn alloys, for example, silicomanganese generally having a Si content of 14% by mass or more.
Japanese Patent Publication No. 5-80541 Japanese Patent Publication No. 60-11099

  The present invention provides an inexpensive method for producing low-phosphorus Mn and Mn alloys suitable for mass production, in which phosphorus contained in Mn and Mn alloys can be reduced to a concentration suitable for manganese addition in steel production. The purpose is to do.

  Another object of the present invention is to provide a method for producing low phosphorus Mn and a Mn alloy that can be applied to other Mn alloys such as silicon manganese having a high silicon content in addition to metal Mn and ferromanganese. It is.

  As described above, the dephosphorization method for removing phosphorus contained in Mn and the Mn alloy includes the oxidative dephosphorization method disclosed in Patent Document 1 and the above-mentioned Patent Document 2. There is a reductive dephosphorization method.

The oxidative dephosphorization method is economically disadvantageous because the most effective dephosphorization agent having a high basicity is an expensive barium compound. On the other hand, the dephosphorization agents used in the reductive dephosphorization method disclosed in Patent Document 2 are all CaC ₂ (used for generating calcium carbide, acetylene gas, etc.) and CaF, which are used in large quantities industrially. ₂ (naturally produced as calcium fluoride and fluorite and used as a flux for iron making and metal refining), it is much cheaper and stable supply is possible. Further, with respect to the ultimate phosphorus concentration and the dephosphorization rate, the reductive dephosphorization method disclosed in Patent Document 2 has obtained better results.

The present inventors, focusing on the advantages of such reducing dephosphorization method, a dephosphorization flux which is based on CaC ₂ -CaF ₂ system, phosphorus concentration reaches a stable 0.02 wt% or less The method that can be realized in this way was intensively studied. Furthermore, the conditions for suppressing carbon pickup, which is one of the drawbacks when using CaC ₂ , to a minimum were examined.

  First, the relationship between the hatchability of the flux and the amount of impurities on the dephosphorization limit was examined. That is, hatchability, the amount of impurities and the dephosphorization limit are mutually related. Next, in the reductive dephosphorization by the flux, as defined in Patent Document 2, the carbon concentration and silicon concentration in the molten metal and dephosphorization are closely related, so that these concentrations are limited. However, it prevented the application of reductive dephosphorization to silicomanganese. If the allowable range of the carbon concentration and the silicon concentration in the molten metal is widened, it becomes possible to apply reductive dephosphorization to silicomanganese, and there are great industrial advantages.

Therefore, when the mechanism and preferred conditions related to reductive dephosphorization were examined, the carbon concentration and the silicon concentration not only affected the mutual solubility, but both affected the oxygen concentration. Found to affect. That is, attention was focused on the oxygen concentration in the molten metal, which was not considered in the past. By reducing the oxygen concentration in the molten metal, not only the dephosphorization rate and the ultimate dephosphorization concentration are greatly improved, but also the restriction of the carbon concentration and the silicon concentration can be relaxed, and further the carbon pickup from CaC ₂ can be suppressed. became. As a result, in addition to improving the dephosphorization rate and dephosphorization limit, the applicable range of carbon and silicon concentrations could be significantly expanded.

  Second, considering that low temperature treatment is advantageous for reductive dephosphorization, the relationship between the treatment temperature and dephosphorization was examined. I got new knowledge that there was a range.

  Thirdly, in order to avoid carbon contamination due to the carbon pickup, which is a drawback of the above flux, while further promoting reductive dephosphorization, the specific condition is based on the idea of replacing a part thereof with Ca and / or Ca alloy. Added consideration. As a result, it was found that by replacing part of the flux with Ca and / or Ca alloy, not only carbon contamination is prevented, but also a clear reduction effect can be obtained with respect to the ultimate phosphorus concentration. This makes it possible to apply the reductive dephosphorization method to a molten metal having a higher carbon concentration and a higher silicon concentration.

The present invention completed on the basis of the above findings is a molten Mn or Mn alloy having a carbon concentration of 2.0% by mass or less and an oxygen concentration of 0.5% by mass or less and containing Mn of 60% by mass or more. Using a flux containing at least 80% of CaF ₂ and CaC _{2 and} having a mass ratio of (CaC ₂ ) / {(CaC ₂ ) + (CaF ₂ )} × 100 = 30 to 65%, A dephosphorization treatment is performed at a molten metal temperature of 1350 to 1500 ° C.

  The dephosphorization treatment can be performed by adding at least one metal Ca source selected from metal Ca and Ca alloy in addition to the flux. Thereby, further low phosphatization and improvement in dephosphorization efficiency can be obtained, and an increase in carbon concentration due to dephosphorization treatment is suppressed.

  According to the present invention, a metal having an extremely low phosphorus concentration such as a phosphorus concentration of 0.03 mass% or less, preferably 0.02 mass% or less, which can be used as a high added-value ironmaking auxiliary material in place of very expensive electrolytic manganese. It becomes possible to mass-produce Mn and Mn alloys at low cost. The method of the present invention can be applied to the production of Mn and Mn alloys having a wide range of carbon concentrations and silicon concentrations, and can also be applied to the production of high silicon manganese alloys such as silicomanganese.

The present invention stabilizes a low phosphorus Mn or Mn alloy having a phosphorus concentration of 0.02% by mass or less by reducing dephosphorization of Mn or Mn alloy using a dephosphorization flux based on the CaC ₂ -CaF ₂ system. It aims to manufacture.

The mechanism of reductive dephosphorization using the above flux is represented by the following reaction formula:
3CaC ₂ + 2P = Ca ₃ P ₂ (s) + 6C (2)
CaC ₂ is decomposed into Ca and C, and the produced Ca combines with P to perform dephosphorization. C released by the decomposition is absorbed by the molten metal. The other flux component, CaF ₂ , acts as a fluxing agent for the liquid phase of the flux.

  According to this formula, the reaction efficiency was expected to increase as the carbon concentration in the molten metal before treatment (that is, molten Mn or Mn alloy) was reduced. However, as will be described later, in the experiment, the carbon concentration in the molten metal was The effect was saturated at 2.0% by mass, and it was found that even if the carbon concentration was lowered, the effect of reducing the ultimate phosphorus concentration was small. Therefore, in this invention, the carbon concentration of the molten Mn or Mn alloy which is a molten metal shall be 2.0 mass% or less. When the carbon concentration of the molten metal exceeds 2.0% by mass, the reaction efficiency of dephosphorization is lowered for the above reasons, and the dephosphorization becomes insufficient and the dephosphorization rate is lowered. In consideration of an increase in the carbon concentration of the molten metal after the dephosphorization treatment due to carbon absorption during the dephosphorization treatment and further improvement of the dephosphorization efficiency, the carbon concentration of the molten metal is preferably 1.5% by mass or less.

  With respect to carbon, since Mn or Mn alloy of raw material does not increase from the surrounding atmosphere or refractory after melting, Mn having a carbon concentration of 2.0% by mass or less, preferably 1.5% by mass or less as a melting raw material Alternatively, a Mn alloy raw material may be used.

Oxygen is a factor that inhibits reductive dephosphorization using the flux. That is, the reaction with oxygen as shown in the following formula (3):
CaC ₂ + 1 / 2O ₂ = CaO + 2C (3)
When CaC ₂ is oxidized according to the above formula, it is natural that it does not contribute to dephosphorization. However, the generated CaO increases the activity of CaC ₂ and CaF ₂ , thereby increasing the solid phase ratio of the flux melt. In addition, it acts to hinder the dissolution of Ca ₃ P ₂ produced by reductive dephosphorylation, and the liberated carbon is absorbed by the molten metal, increasing the carbon concentration of the molten metal. As the oxygen source, oxygen in the molten metal, oxygen contained in the impurities of the flux, and oxygen dissolved in the molten metal from the refractory containing the atmosphere and the molten metal are conceivable.

  Therefore, when these oxygen sources were examined, oxygen in the molten metal most affected the dephosphorization reaction, and the lower the oxygen concentration in the molten metal, the higher the dephosphorization rate, and further, oxygen and Ca reacted. It was found that the basic unit of the dephosphorization flux can be reduced because the inhibition of dephosphorization due to the above can be suppressed. That is, even if other allowable oxygen sources described later are taken into account, if the oxygen concentration of the molten metal is 0.5 mass% or less, it is possible to dephosphorize to a phosphorus concentration of 0.03 mass% or less. Desirably, the oxygen concentration is 0.4% by mass or less, and in this case, it is possible to stably dephosphorize the phosphorus concentration to 0.02% by mass or less.

Therefore, in the present invention, the molten Mn or Mn alloy, which is the molten metal to be dephosphorized, has an oxygen concentration of 0.5 mass% or less, preferably 0.4 mass% or less. When the oxygen concentration in the molten metal is high, a treatment for reducing the oxygen in the molten metal is performed prior to dephosphorization, and the oxygen concentration is controlled as described above. The deoxidation method for that is not specifically limited. For example, there is a method of appropriately adding silicon and / or aluminum that has an affinity for oxygen and can be expected to have a deoxidizing effect within a range that does not affect alloy-required components and dephosphorization. In the latter case, the effect is recognized when the Al concentration is 0.1% by mass, and the effect is saturated at 2.0% by mass. At that time, it is also possible to deoxidize by adding CaF ₂ flux. In this case, it is appropriate to remove the added flux before dephosphorization in consideration of the influence on the subsequent dephosphorization process.

Oxides contained as impurities contained in the flux also serve as oxygen sources. In CaC ₂ used industrially, the CaC ₂ purity is generally about 80% to 90% by mass, and the balance is CaO and impurities contained in production. Although higher CaC ₂ purity is desirable, since CaO is also a dephosphorization reaction product, the initial concentration is allowed up to 10% by mass with respect to the total flux. As CaF ₂ , naturally produced fluorite is generally used, and its purity is about 95 to 99% by mass, and SiO ₂ can be mentioned as a main impurity. A lower SiO ₂ concentration is desirable, but on the other hand, it has the effect of lowering the activity of the generated CaO, and up to 5% by mass is allowed for the total flux.

There is a refractory that contains molten metal as a third oxygen source. As refractories suitable for holding molten metal of Mn and Mn alloys, basic chemical refractories mainly composed of MgO and CaO, MgOAl ₂ O ₃ refractories, MgOCr ₂ O ₃ refractories, which have high chemical stability against these melts There are refractories. A refractory in the region holding the flux is considered to have a higher basicity. By using such a stable basic refractory, performing an efficient dephosphorization process in a short time, and increasing the treatment amount per time, the influence of oxygen from the refractory can be minimized. In addition, since the dephosphorized flux easily melts the refractory, it may contain MgO and Al ₂ O ₃ which are stable oxides in the flux from the viewpoint of suppressing the refractory of the refractory that holds the flux. In that case, up to 5% by mass is permitted.

  As a fourth oxygen source, there is oxygen dissolved in the molten metal from the atmosphere. Therefore, in the present invention, the dephosphorization is preferably performed in an atmosphere in which the atmosphere is shut off, for example, in an inert gas (typically argon gas) atmosphere. In this way, oxygen from the atmosphere can be substantially ignored. If it is difficult to completely shut off the atmosphere from the atmosphere in actual operation, the dephosphorization atmosphere is allowed to contain some atmosphere.

To achieve sufficient dephosphorization effect, the flux mainly containing CaC ₂ and CaF ₂ is to use a total amount of CaC ₂ and CaF ₂ is 80 mass% or more. The balance of the flux is composed of components (CaO, SiO _2, etc.) contained as impurities in CaC ₂ or CaF ₂ and components (CaC ₂ , CaF _2, etc.) added for the purpose of protecting refractories in some cases. . The balance by mass%, CaO 10% or less, SiO ₂ is less than 5%, MgO 5% or less, Al ₂ O ₃ or less, and as much as possible a small amount of inevitable impurities is acceptable.

The ratio of CaC ₂ and CaF _{2 in} the flux should be a ratio having a liquid phase, dissolving the reaction products Ca ₃ P ₂ and CaO to some extent, and a ratio at which sufficient Ca is supplied. is there. Therefore, CaC _{2 with} respect to the total amount of both components represented by [(CaC ₂ ) / {(CaC ₂ ) + (CaF ₂ )} × 100) (wherein the parenthesis is the mass% of the component in the flux). So that the mass ratio is in the range of 30 to 65%. In this mass ratio is less than 30%, can not be formed in an amount sufficient to CaC ₂ -CaF ₂ melt in the liquid phase, until the phosphorus concentration of 0.03 wt% or less, preferably reaches 0.02 mass% or less I can't dephosphorize. On the other hand, when the mass ratio exceeds 65%, a decrease in the liquid phase ratio due to the formation of the CaC ₂ solid phase becomes remarkable, the reaction rate decreases, and the reaction product Ca dissolves in the molten metal. After that, it becomes impossible to sufficiently dephosphorize until the phosphorus concentration as described above is reached. In addition, since most of the C contained in the added CaC ₂ is absorbed by the molten metal, the increase in the carbon concentration of Mn and the Mn alloy after dephosphorization becomes significant.

  When the molten metal is a Mn alloy, the Mn content of the molten metal is 60% by mass or more. This is because when the Mn content is 60% by mass or more, it becomes practically difficult to apply oxidative dephosphorization generally performed in the steelmaking process, and the liquidus temperature of the molten metal becomes 1300 ° C. or less. It is. Thereby, the advantage of the present invention based on the reductive dephosphorization method can be enjoyed. Mn alloys suitable for dephosphorization according to the method of the present invention include ferromanganese (Mn—Fe alloy) with an Fe content of 25% by mass or less, and silicomanganese (Mn—Si) with an Si content of 23% by mass or less. Alloy).

The dephosphorization treatment is performed by adding the aforementioned CaF ₂ -CaC ₂ -based flux to a molten Mn or Mn alloy adjusted so that the carbon concentration and the oxygen concentration do not exceed the above-mentioned upper limits, and preferably an inert gas ( Usually, it is performed at a molten metal temperature of 1350 to 1500 ° C. in an atmosphere of argon gas.

  The amount of flux added can be estimated by the phosphorus concentration before treatment of the melt to which the dephosphorization treatment is applied, the target reached phosphorus concentration, the oxygen concentration before treatment of the melt that consumes the dephosphorization element Ca, the carbon concentration and the silicon concentration. Consider factors that are directly involved in dephosphorization, such as dephosphorization rate, and factors that are indirectly involved in dephosphorization, such as the consumption of Ca, which is a dephosphorizing element, due to the effects of refractories and atmospheres used. Can be set.

As shown in (2) above, the dephosphorization by Ca generated by the decomposition of CaC ₂ is accompanied by the release of C. Moreover, this dephosphorization is affected by the oxygen concentration, carbon concentration, treatment temperature, and flux composition of the molten metal as described above. In order to further promote dephosphorization, improve stability, and suppress increase in carbon concentration, it is advantageous to increase the amount of Ca supplied to the molten metal. That is, in addition to the dephosphorization flux, a metal Ca supply source is supplied to the molten metal, and the dephosphorization shown in the above equation (1) without carbon release is performed in parallel.

However, the metal Ca is an active metal having a high vapor pressure, and only the phase diagrams of the Ca—CaF ₂ system and the Ca—CaO system are known regarding the phase equilibrium of the dephosphorization flux to which Ca is added. The metal Ca or Ca alloy because it is expensive in comparison with CaC _2, it is necessary to use it effectively.

In a preferred embodiment of the present invention, in addition to the CaF ₂ -CaC ₂ -based dephosphorization flux described above, at least one metal Ca source selected from metal Ca and Ca alloy is added to perform the dephosphorization treatment. . Thereby, dephosphorization can be performed more stably and efficiently while mitigating the increase in the C concentration of the molten metal. As the Ca alloy, industrially produced Ca alloys such as calcium silicon alloy and calcium aluminum alloy can be used.

  The addition amount of the metal Ca source is preferably 15% by mass or less, more preferably 10% by mass or less, in terms of Ca metal, with respect to the flux. If the added amount of the metallic Ca source is too large, heat generation due to evaporation or oxidation reaction of Ca, cost deterioration due to expensive metal such as Ca or Ca alloy, and the like occur. Further, when the metal Ca source is a Ca alloy, most of the alloy elements (eg, silicon or aluminum) are transferred to the molten metal, so that the allowable component amount as the Mn alloy is exceeded or oxidized to form an oxide. It may shift to flux and worsen the dephosphorization rate. In order to sufficiently obtain the effect of the metallic Ca source, it is preferable to add the metallic Ca source in such an amount that the added amount is 1% by mass or more, particularly 3% by mass or more.

  When the metal Ca source is used in combination, the dephosphorization effect of the metal Ca source can be obtained, so that the amount of the dephosphorization flux described above can be reduced. By suppressing the addition amount of the dephosphorization flux in this way, an increase in the carbon concentration of the molten metal due to dephosphorization can be suppressed.

  The addition of the metallic Ca source is preferably performed after the addition of the dephosphorization flux so that the metal Ca source is supplied to the molten metal via the dephosphorization flux. The effect of improving the dephosphorization efficiency appears more markedly when calcium silicon alloy or calcium aluminum alloy is used than metal Ca. However, Si or Al pick-up is generated in the molten metal, and depending on the composition, for example, the Si concentration may exceed 1.5% by mass, so it should be applied to applications that allow this.

  The lower dephosphorization temperature (molten metal temperature) was expected to increase the dephosphorization limit and increase the dephosphorization efficiency. However, as will be described later, the dephosphorization rate actually decreased at 1350 ° C. or below. . Therefore, it is set as the range of 1350-1500 degreeC.

  The dephosphorization treatment is preferably performed while stirring the molten metal in order to improve the reaction efficiency. This stirring can be performed using stirring means such as electromagnetic induction, but gas stirring is advantageous in terms of stirring strength, equipment investment, and maintenance. For example, the molten metal and the flux can be agitated by blowing an inert gas (eg, argon gas) into the molten metal by bottom blowing. In this case, dephosphorization can be performed using a refining furnace capable of blowing gas from the bottom, for example, a ladle refining furnace capable of holding the ladle in an inert gas atmosphere.

  The dephosphorization time may be selected so as to achieve the amount of molten metal to be dephosphorized and the target low phosphorus concentration, but it is usually preferable to be within a range of 3 to 30 minutes. After the treatment, the generated dephosphorization slag is removed according to a conventional method, and the dephosphorized Mn or Mn alloy is obtained by casting the molten metal dephosphorized from the container into a mold.

  Next, the results of experiments that are the basis of the present invention will be described. In the experiment, a dephosphorization test of 1.5 kg of 80% Mn-18.5% Fe alloy molten metal was performed using a small Tamman furnace in which the inside of the furnace could be an argon gas atmosphere. The P concentration before treatment before dephosphorization was 0.20% by mass, the carbon concentration was 0.1-3.0% by mass, and the silicon concentration was 0.50% by mass.

As the dephosphorization flux, reagent grade CaC ₂ (CaC ₂ purity 81.4% by mass) and CaF ₂ (CaC ₂ purity 99.0% by mass) were used. The blending ratio was based on 60 mass% CaC ₂ and the total amount of flux added was 150 g. The reaction temperature was basically 1400 ° C. and varied depending on the case. A dense magnetic crucible was used as a molten metal holding container, and argon gas was blown at a flow rate of 0.3 Nl / min to stir the molten metal and slag. The dephosphorization time after adding the dephosphorization flux was 8 minutes.

  FIG. 1 shows the relationship between the initial oxygen concentration and the reached P concentration, which is the phosphorus concentration 8 minutes after the addition of the dephosphorization flux. FIG. 2 shows the relationship between the initial carbon concentration and the reached P concentration, and FIG. 3 shows the relationship between the initial carbon concentration and the dephosphorization rate 8 minutes after the addition of the dephosphorization flux.

  As shown in FIG. 1, when the initial oxygen concentration is 0.5% by mass or less, the reached P concentration is 0.030% by mass or less, and when the initial oxygen is 0.4% by mass or less, the reached P concentration is 0.020% by mass or less. Can be taken off. As shown in FIGS. 2 and 3, when the carbon concentration is 2.0% by mass or less, the ultimate P concentration is 0.030% by mass or less, and when the carbon concentration is 1.5% by mass or less, the ultimate P concentration is stably 0.5%. The dephosphorization rate at that time becomes 90% or more.

FIG. 4 shows the relationship between the melt treatment temperature and the dephosphorization rate 8 minutes after the addition of the dephosphorization flux. When the molten metal temperature is in the range of 1350 ° C. or more and 1500 ° C. or less, a dephosphorization rate of 90% or more can be obtained. The reason that the dephosphorization rate decreases when the molten metal temperature is high is that the dephosphorization limit of the dephosphorization reaction decreases. Moreover, the reason why the dephosphorization rate decreases when the molten metal temperature is lowered is that the hatchability of the dephosphorizing flux is deteriorated and the dissolution rate in the molten Mn and Mn alloy due to the decomposition reaction of CaC ₂ is decreased. It is estimated that.

FIG. 5 shows the relationship between the component mass ratio of the dephosphorization flux and the dephosphorization rate 8 minutes after the addition. A dephosphorization rate of 90% or more can be obtained when the mass ratio is (CaC ₂ ) / {(CaC ₂ ) + (CaF ₂ )} × 100 = 30 to 65%.

  As described above, when a metal Ca source is added in addition to the dephosphorization flux, further dephosphorization can be promoted while suppressing carbon pickup. FIG. 6 and FIG. 7 show the reached P concentration when the metal Ca and the CaSi alloy are added immediately after the addition of the flux in amounts such that the mass ratio of the Ca metal to the flux is 0.05 and 0.10 (flux addition 8). Minutes, left axis) and ΔC (the amount of increase in carbon concentration after treatment relative to the initial carbon concentration (mass%), right axis).

As can be seen from the figure, when the added amount of these metallic Ca sources is 5 mass% or more as Ca metal with respect to the CaC ₂ -CaF ₂ dephosphorization flux, the effect of stabilizing the ultimate P concentration and the dephosphorization rate is obtained. In addition, the carbon pickup (ΔC) can be suppressed by about 10%. When this addition amount is 10% by mass or more, the reached P concentration is less than 0.015% by mass, and the dephosphorization rate at that time can be expected to be 93% or more. Calcium silicon alloy has a higher dephosphorization promoting effect than metallic Ca. When 10% by mass or more is added to the flux in terms of Ca metal, the reached P concentration is less than 0.010% by mass, and the dephosphorization rate. Becomes 95% or more. In addition, when a calcium silicon alloy is used, carbon pickup can be suppressed by about 20%.

  Finally, based on this experiment, the relationship between flux addition and dephosphorization will be described more specifically. The amount of flux added needs to consider the amount of Ca contained in the flux. That is, the amount of Ca directly consumed by the dephosphorization reaction and the amount of Ca indirectly consumed by the molten metal amount and the selection process.

When using the CaC ₂ -40 wt% CaF ₂ in the flux, the amount of Ca amount per 100g melt 1kg is about 30.4 g. Ca consumed for dephosphorization per 1 kg of molten metal is approximately 4.0 g as dephosphorization concentration Δ “% P” = 0.182%, and Ca consumed for deoxidation of molten metal is deoxidation concentration Δ “% O”. Since it is about 0.4% by mass, it is 10.0 g, and when the dephosphorization, the Ca concentration contained in the molten metal is about 0.05% by mass, it is 0.5 g. That is, about 47% is a necessary amount of Ca. On the other hand, the indirectly consumed Ca related to this experimental condition is about 10.9 g of Ca reduced by reducing the crucible material MgO, and about 5.3 g of Ca consumed due to oxidation from the atmosphere and unknown reasons. It is. That is, about 53% is the amount of Ca consumed indirectly.

  The amount of flux and the amount of metallic Ca source used as described above take into account the pre-treatment phosphorus concentration, target post-treatment phosphorus concentration, dephosphorization rate and pre-treatment oxygen concentration, and the amount of Ca consumed indirectly depending on the selected process. And decide.

  In a refining furnace capable of adjusting the atmosphere of the high frequency induction heating method, a molten metal of 77% Mn—Fe alloy having a carbon concentration of about 1% by mass was heated to a predetermined temperature of about 1400 ° C. to be melted. The temperature of the molten metal was adjusted by controlling the high frequency output. Table 1 shows the results of measuring the composition (Mn, C, Si, P, and O concentration) of the molten metal after melting.

The melt in the furnace, the dephosphorization flux mixed with CaF ₂ in a predetermined ratio to be used as an industrial CaC ₂ and steelmaking auxiliary materials were added. The purity of CaC ₂ was 81.4% by mass, and the purity of CaF ₂ was 99.0% by mass. The addition amount of the dephosphorization flux was 23 to 28.5 kg per ton of molten metal. The atmosphere during the treatment was Ar gas (1 atm). In order to stir the molten metal and slag, argon gas was introduced at a flow rate of 15 Nl / min from two furnace bottom porous bricks.

  The dephosphorization flux added to the melt immediately melted. After the addition of the flux, dephosphorization treatment was performed for 20 minutes. After the treatment, the refining furnace was tilted to separate the dephosphorization slag, and then the dephosphorized Mn alloy melt was poured onto a mold and cast to prepare a Mn alloy. Table 1 shows the added amount of flux and its components, the treatment temperature, the C and P concentrations after dephosphorization, and the dephosphorization rate.

  As shown in Table 1, in the examples a to e of the present invention, it was possible to obtain 0.03 mass% or less in the reached P concentration and 85% or more in the dephosphorization rate. In particular, in Examples d and e in which the oxygen concentration before treatment was lower than 0.40% by mass, the reached P concentration was 0.018% by mass or less and the dephosphorization rate was 90% or more.

  On the other hand, in Comparative Example f, the oxygen concentration in the molten metal before dephosphorization was as high as 0.55% by mass, and the ultimate P concentration was 0.043% by mass despite the dephosphorization treatment under the same conditions as in the examples. The dephosphorization rate did not reach 80%.

In comparative example g, the dephosphorization flux has a CaC ₂ / (CaC ₂ + CaF ₂ ) ratio higher than the range of the present invention, comparative example h is lower than the range of the present invention, and comparative example i is dephosphorized. In this case, the concentration of (CaC ₂ + CaF ₂ ) in the flux was lower than the range of the present invention, but in all cases, the reached P concentration exceeded 0.04 mass% and the dephosphorization rate did not reach 80%.

  Comparative Example j is a case where the dephosphorization temperature is higher than the range of the present invention, and Comparative Example k is a case where the dephosphorization temperature is lower than the range of the present invention. In either case, the ultimate P concentration is 0.04% by mass. The dephosphorization rate was less than 80%.

As in Example 1, a refining furnace capable of high-frequency induction heating type atmosphere adjustment, and a 1.3% molten 77% Mn-Fe alloy (partially a silicomanganese alloy) with a carbon concentration of about 1.0 mass. Dissolution was performed. Thereafter, a dephosphorization flux in which the same CaC ₂ and CaF ₂ as in Example 1 were mixed in the furnace, and then metal Ca or CaSi alloy was added as a metal Ca source. The metal Ca had a purity of 98% by mass, and the CaSi alloy was composed of Ca: 30% by mass, Si: 60% by mass, the balance iron and inevitable impurities. The addition amount of the dephosphorization flux is 19 to 24 kg per ton of the molten metal, and the addition amount of the metallic Ca source is 0.2 to 2.1 kg per 1 ton of the molten metal (about 3.3 to 10% by mass with respect to the flux). there were. The reaction temperature was basically 1400 ° C., and the high-frequency output was controlled so that the desired temperature was obtained. The atmosphere during the treatment was Ar gas (1 atm). In order to stir the molten metal and slag, argon gas was introduced at a flow rate of 15 Nl / min from two furnace bottom porous bricks.

  Dephosphorization treatment was performed for 20 minutes after the addition of the dephosphorization flux. After the treatment, the furnace was tilted to separate the dephosphorization slag, and then the dephosphorized molten Mn alloy was poured onto a mold and cast to prepare a Mn alloy. Table 2 shows the dephosphorization treatment conditions and the alloy compositions before and after the treatment.

  As shown in Table 2, the initial oxygen concentration before the treatment is higher than 0.4% by mass (that is, 0.4% by mass) as compared with the result b of Example 1 in which the metal Ca source shown in Table 1 is not added. Even in the case of more than 0.5% by mass or less), the reached P concentration further decreased to 0.012 to 0.015% by mass, and the dephosphorization rate exceeded 90% (l, n).

  Comparing the examples in which the initial oxygen concentration is 0.4% by mass or less, in m and o in Table 2, the ultimate P concentration is 0.1 in comparison with d and e in Table 1 in which the metal Ca source was not added. 008 to 0.009% by mass, and the dephosphorization rate was higher than 95%.

  P in Table 2 is a dephosphorization treatment with a molten Mn alloy corresponding to silicomanganese. Even for silicomanganese, which has not been efficient in reducing dephosphorization in the past, by performing the dephosphorization process according to the present invention, the ultimate P concentration was 0.019% by mass and the dephosphorization rate was 81%. Further, q in Table 2 shows an example of dephosphorization of an Mn alloy having a Mn content exceeding 90% by mass. The reached P concentration was 0.005% by mass and the dephosphorization rate was 90%. From this result, it was speculated that the method of the present invention can be applied to metal Mn, and it was confirmed that the result equivalent to q in Table 2 was obtained when actually applied to metal manganese.

In Example 2, although the amount of flux added was smaller than that in Example 1, the reached P concentration was lower than in Example 1 and the dephosphorization rate was improved. Further, by reducing the amount of flux, particularly the amount of CaC _{2, the} increase in carbon concentration (carbon pickup) of the molten metal after treatment can be suppressed, and a higher purity Mn alloy can be produced.

The graph which shows the relationship between an initial oxygen concentration and the reached P concentration which is a phosphorus concentration 8 minutes after adding the flux for dephosphorization. The graph which shows the relationship between initial carbon concentration and ultimate P concentration. The graph which shows the relationship between an initial carbon concentration and the dephosphorization rate in 8 minutes after the flux for dephosphorization is added. The graph which shows the relationship between molten metal processing temperature and a dephosphorization rate. The graph which shows the relationship between the component mixing mass ratio [(CaC ₂ ) / {(CaC ₂ ) + (CaF ₂ )} × 100] of the dephosphorization flux and the dephosphorization rate. The graph which shows the relationship between the reached P density | concentration and (DELTA) C density | concentration when adding metal Ca in the ratio from which the mass ratio with respect to a flux will be 0.05 and 0.10. The graph which shows the relationship with the ultimate P density | concentration and (DELTA) C density | concentration when a CaSi alloy is added in the ratio from which the mass ratio with respect to a flux becomes 0.05 and 0.10.

Claims (2)

A molten Mn or Mn alloy having a carbon concentration of 2.0% by mass or less and an oxygen concentration of 0.5% by mass or less and containing Mn of 60% by mass or more, and CaF ₂ and CaC ₂ in total of 80% or more And dephosphorizing at a melt temperature of 1350-1500 ° C. using a flux whose mass ratio is (CaC ₂ ) / {(CaC ₂ ) + (CaF ₂ )} × 100 = 30-65%. A method for producing Mn and a Mn alloy.   The method for producing Mn and Mn alloy according to claim 1, wherein in addition to the flux, at least one metal Ca source selected from metal Ca and Ca alloy is added to perform dephosphorization treatment.

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