JP2003049235A - Chromium-containing metal and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high Cr-containing metal containing >=85% Cr, and having low contents of Al, Si and S, and to provide a production method therefor. SOLUTION: The high Cr-containing metal is produced by an arc melting furnace, and has a composition containing >=85% Cr, <=0.005% Al, <=0.1% Si and <=0.002% S. In the method for producing the high Cr-containing metal, chromium oxide heated and melted by an arc melting furnace is reduced with Si to obtain molten metal containing >=85% Cr. Next, slag produced by the Si reduction is discharged from the arc melting furnace, and basic flux is newly added to the inside of the arc melting furnace to melt the basic flux by an arc. Slag produced by the melting of the basic flux and the above molten metal are contacted to refine the molten metal. After that, the molten metal is tapped from the arc melting furnace, and is cast.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to electronic materials, corrosion resistance, and
The present invention relates to high-purity metallic chromium or ferrochrome used for heat-resistant superalloys (super alloys) and the like, and methods for producing these.

[0002]

2. Description of the Related Art In electronic materials and corrosion-resistant / heat-resistant superalloys, high-purity metallic chromium and ferrochrome with few impurities are used. Hereinafter, in the present invention, these metallic chromium and ferrochrome are collectively referred to as chromium-containing metals. An ore that can be economically obtained as a chromium source of this chromium-containing metal is chromite (chromite: FeO.Cr ₂ O ₃ ), but since it contains a large amount of iron, the Cr component of ferrochrome obtained from chromite. The upper limit is about 72% by mass.
Therefore, chromium oxide (Cr ₂ O ₃ ) obtained by refining chromite is generally used as a raw material for metallic chromium.

As a method for producing metallic chromium, for example, an aluminum thermit method for reducing powdery chromium oxide with metallic aluminum powder as disclosed in JP-A-60-36632 and JP-B-58- A silicon reduction method in which chromium oxide is melted in an arc furnace and reduced with metallic silicon, as disclosed in the method for producing a high-purity chromium iron alloy in Japanese Patent No. 7700, and in Japanese Patent Laid-Open No. 62-47436. An electrolytic reduction method is known in which a chromium salt solution is electrolytically reduced to deposit metallic chromium on the cathode. Each of these known manufacturing methods has advantages and disadvantages.

[0004] For example, in the aluminum thermite method, metallic chromium can be easily produced with a simple facility, but since it is a batch method, the throughput per batch is small, the production efficiency is low, and it is used as a reducing agent. Metallic aluminum is expensive and expensive to manufacture. Further, aluminum as a reducing agent remains in the produced metallic chromium, and since the refractory component for the furnace material is reduced and mixed in the metallic chromium due to the strongly reducing atmosphere, it may be mixed in the metallic chromium. There are also problems.

In the silicon reduction method, metallic silicon as a reducing agent is less expensive than metallic aluminum, and since silicon can stoichiometrically reduce oxygen in an amount smaller than aluminum, chromium oxide is heated and heated. In consideration of the amount of electric power used for manufacturing, it can be manufactured at a lower cost than the aluminum thermite method. Furthermore, continuous production by an arc furnace is also possible, and the production efficiency is high, which is also advantageous compared with the aluminum thermite method from this point. However, about 0.7% by mass of silicon as a reducing agent remains in the produced metallic chromium, which is a serious quality problem.

In the aluminum thermite method and the silicon reduction method, if the amount of metal aluminum or metal silicon as a reducing agent is reduced to produce a metal in a state of insufficient reduction, the amount of aluminum and silicon remaining in the metal chromium will be reduced. In addition, the reduction yield of chromium oxide deteriorates, and the amount of oxygen in the produced metallic chromium increases, which causes new problems in terms of production cost and quality.

The electrolytic reduction method can produce relatively high-purity metallic chromium, but it uses Cr ₂ (S
Since O ₄ ) ₃ is used, 0.02 to 0.03 mass% of sulfur is contained in the produced metal chromium, and
Oxygen is contained in an amount of 0.3 to 1% by mass and nitrogen is included in an amount of 0.02 to 0.05% by mass because the electrolysis is performed in an aqueous solution. Further, there are also economic problems that the refining of the chromium salt solution requires a lot of treatments to complicate the process, the equipment cost is high, and the power consumption is great.

Ferrochrome having a chromium content of 72% by mass or more cannot be produced by only one reduction refining of chromite as described above. Therefore, for example,
As disclosed in Japanese Patent No. 4897, it is manufactured by deferring ferrochrome once manufactured by acid treatment or the like. However, it is difficult to say that the conventional iron removal treatment including this method has a complicated treatment process and is high in production efficiency.

[0009]

The requirements for chromium-containing metals represented by metallic chromium used in electronic materials, corrosion-resistant and heat-resistant superalloys, etc. are high purification and reduction in manufacturing cost. On the other hand, as described above, the chromium-containing metal produced by the conventional method has a high content of any impurity element, and a high purity has a high production cost, and both of them are simultaneously produced. It is hard to say that I am satisfied.

The present invention has been made in view of the above circumstances.
It is an object of the invention to provide a method for economically and efficiently producing a chromium-containing metal having a low content of impurities such as aluminum, silicon, and sulfur.
Another object of the present invention is to provide a chromium-containing metal containing a small amount of impurity elements produced by this production method.

[0011]

Means for Solving the Problems The present inventors have investigated a method for efficiently and inexpensively producing a chromium-containing metal that has a low content of impurities and can be used for electronic materials and corrosion-resistant / heat-resistant superalloys. did. Then, focusing on the silicon reduction method, which has the least fluctuating cost among the conventional techniques, a method for removing silicon remaining in the molten metal in the silicon reduction method was examined. As a result, it was found that silicon can be easily removed by producing a molten metal by the silicon reduction method, discharging the slag, and then refining it in the presence of an appropriate flux. That is, it was found that a chromium-containing metal having a low content of aluminum, silicon, and sulfur can be manufactured at low cost.

The present invention has been made on the basis of the above-mentioned findings. The primary step of reducing a chromium oxide with silicon to obtain a molten metal, and discharging the slag produced in this primary step,
And a secondary step of refining the molten metal by adding a basic flux.

One aspect of the method for producing a chromium-containing metal of the present invention is to reduce chromium oxide heated and melted in an arc melting furnace with silicon to obtain a molten metal containing 85 mass% or more of chromium, Then, the slag generated by this silicon reduction is discharged from the arc melting furnace, and after discharging the slag, a basic flux is newly added into the arc melting furnace to melt the basic flux in the arc and The slag generated by melting the flux and the molten metal are brought into contact with each other to refine the molten metal, and then the molten metal is discharged from the arc melting furnace and cast.

Since CaO has a high desulfurization ability and can be obtained at a low cost, it is preferable that the basic flux contains CaO as a main component. Also, gas components such as nitrogen and oxygen in the chromium-containing metal are removed by heat treatment in a vacuum atmosphere, and a more pure chromium-containing metal can be produced. Heat treatment is preferable. By this treatment, the nitrogen content in the chromium-containing metal can be made 0.005% or less. Further, it is more preferable that the chromium-containing metal is crushed, then shaped into a briquette, and then vacuum heat treated.

In the present invention, chromium oxides such as chromium oxide and chromite are reduced with silicon in the primary step, and the molten metal after discharging slag in the secondary step is refined with a basic flux to remove chromium-containing metal. To manufacture. As described above, since aluminum is not used as a reducing agent, the produced chromium-containing metal has an aluminum content of 0.005.
The content may be less than or equal to mass% (hereinafter simply referred to as "%"). Further, since silicon is used as a reducing agent, silicon is contained in the molten metal immediately after the reduction smelting in an amount of about 0.2 to 1.0%. It can be reduced to the following. Further, since the generated metal melt is refined by the basic flux, the sulfur in the metal melt is removed in the basic flux, and the sulfur content of the chromium-containing metal produced can be 0.002% or less. .

That is, regarding the quality of the chromium-containing metal according to the present invention, regarding the quality, there are problems of aluminum content in the aluminum thermite method, problems of silicon content in the silicon reduction method, and problems of sulfur content in the electrolytic reduction method. With respect to the manufacturing cost, continuous production by an arc melting furnace is possible, and since inexpensive silicon is used as a reducing agent, the production can be performed at a lower cost than the aluminum thermite method and the electrolytic reduction method.

By the way, the silicon reduction method used in the conventional method for producing ferrochromium, etc.
This is a one-step smelting method in which basic flux is charged into an arc melting furnace and refined while heating. On the other hand, the present invention is a two-stage smelting method in which chromium oxide is reduced by silicon in the primary step and the molten metal after the slag is discharged in the secondary step is refined with a basic flux.

The conventional general silicon reduction method has a problem that the silicon content is high. If the amount of metallic silicon as a reducing agent is reduced and the production is performed in a state of insufficient reduction (so-called weak reduction state) in order to further reduce the silicon content, the amount of silicon remaining in the metallic chromium is reduced to some extent. However, the reduction yield of chromium oxide deteriorates. Further, when the amount of metallic silicon as a reducing agent is reduced, the concentration of chromium oxide in the slag during operation is maintained high. As a result, the viscosity of the slag during operation increases, and as a result, the reduction reaction rate decreases, so that the concentration of chromium oxide in the slag after operation further increases. Since there is a correlation between the amount of chromium oxide in slag and the amount of oxygen in metallic chromium, if the compounding amount of metallic silicon as a reducing agent is decreased, the amount of oxygen in metallic chromium will also increase.

If a large amount of basic flux is charged at once to reduce the silicon content in the conventional general silicon reduction method, the amount of slag becomes large and the silicon content is not stable. .

On the other hand, in the two-stage smelting method of the present invention, the generated slag is discharged after the primary step. There is a correlation between the amount of silicon oxide in the slag and the amount of oxygen in the metallic chromium, and there is also a correlation with the amount of chromium oxide in the slag and the amount of oxygen in the metallic chromium. By discharging the slag after the primary step, it is possible to prevent the amount of oxygen in the metallic chromium from increasing.
By refining the molten metal with the newly added basic flux, not only the amount of silicon in the metallic chromium but also the amount of oxygen can be reduced. Therefore, the reduction yield of chromium oxide does not deteriorate and the amount of oxygen in metallic chromium is reduced.

The present invention is particularly preferably used for a high chromium content metal containing 85% or more chromium. This is because the chromium-containing metal used for electronic materials and corrosion-resistant / heat-resistant superalloys has a low demand for ferrochrome having a low chromium quality with a chromium content of less than 85%.

The chromium-containing metal of the present invention is a chromium-containing metal produced in an arc melting furnace, containing 85% by mass or more of chromium and having an aluminum content of 0.0.
It is characterized in that the content is 05 mass% or less, the silicon content is 0.1 mass% or less, and the sulfur content is 0.002 mass% or less.

One aspect of the chromium-containing metal of the present invention is a chromium-containing metal produced by a combination of an arc melting furnace and vacuum processing equipment, containing 85% by mass or more of chromium and having an aluminum content of 0. 005 mass% or less, silicon content is 0.1 mass% or less, sulfur content is 0.002 mass% or less, and nitrogen content is 0.005 mass% or less.

Here, the chromium-containing metal is preferably produced by reducing chromium oxide with silicon.

In the method for producing a chromium-containing metal of the present invention, the content of chromium is 85% by mass or more, the content of aluminum is 0.005% by mass or more, or the content of silicon is 0.
1 mass% or more, or sulfur content is 0.002 mass%
The above-mentioned chromium-containing metal is used as a raw material, a basic flux is newly added to this raw material, and the raw material is melted and refined in a melting furnace.

Further, the chromium-containing metal of the present invention contains chromium in an amount of 85% by mass or more and has an aluminum content of 0.
005 mass% or more, or silicon content is 0.1 mass%
Chromium produced by using the above or a chromium-containing metal having a sulfur content of 0.002 mass% or more as a raw material, adding a new basic flux to this raw material, and melting and refining in a melting furnace. It is a contained metal, containing 85 mass% or more of chromium, an aluminum content of 0.005 mass% or less, a silicon content of 0.1 mass% or less, and a sulfur content of 0.002 mass% or less. Is characterized by.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
In the present invention, chromium oxide (Cr ₂ O ₃ ) and / or chromite is used as a chromium oxide serving as a chromium source, and at least one of metallic silicon, ferrosilicon, and silicochrome (Si—Cr) is used as a reducing agent. To use. Among these raw materials, chromite, ferrosilicon, and silicochrome contain a large amount of iron, so when producing metallic chromium, chromium oxide and metallic silicon are used. If necessary, a crude metal produced by an aluminum thermite method or a silicon reduction method may be mixed with chromium oxide as a melting raw material, and various metals containing chromium may be added within the range not departing from the present invention. You may mix. The metallic chromium in the present invention is a chromium-containing metal having a chromium content of 99.0% or more.

Also in the case of producing a chromium-containing metal having a chromium content of 85% or more and less than 99.0%, that is, ferrochrome, chromium oxide and metallic silicon are used as main raw materials, but iron is added depending on the chromium grade. Therefore, the chromium content is adjusted to the target grade by mixing chromite or ferrosilicon and silicochrome. The melting point of chromium oxide is 199
The temperature is 0 ° C., and if the flux is not added, it is difficult to melt even in the arc melting furnace. Further, the reduction efficiency of chromium oxide increases as the basicity (CaO / SiO ₂ ) of the slag increases. Furthermore, silicon oxide (Si
In order to melt O ₂ ) and stabilize the operation, it is desirable to add a flux. For this reason, it is preferable to use a flux containing CaO as a main component (hereinafter referred to as “CaO-based flux”) such as quick lime or limestone when melting the chromium oxide. By using the CaO-based flux, there is an advantage that the produced molten metal is desulfurized. The CaO-based flux is preferably added so that the basicity of the slag at the end of silicon reduction is in the range of 1.3 to 3.0. A strong reducing agent such as aluminum that does not remain in the molten metal may be used as a part of the reducing agent. That is, as the type of the reducing agent, metallic silicon is used as a main raw material, but it is of course possible to use aluminum containing silicon as a main component and carbon containing silicon as a main component in accordance with the quality and the calorific value. Further, fluorite (CaF ₂ ) or the like may be mixed and added in order to adjust the melting point of the slag.

A selected chromium oxide, a reducing agent, and a CaO-based flux are charged into an arc melting furnace according to the chromium grade, and are energized and heated to melt. The arc melting furnace used needs to be tiltable in order to discharge the produced metal melt and to discharge the molten slag. Further, the arc melting furnace is capable of manufacturing various chromium grade products in the same arc melting furnace without contaminating each other,
It is preferable that the furnace body for holding and melting the raw material inside thereof is a replaceable cartridge type. The power source for generating the arc may be direct current or alternating current, and a magnesia stamp or the like can be used as the refractory lining.

During heating / melting in an arc melting furnace, when the graphite electrode comes into contact with the charged material, especially the molten metal produced by the reduction reaction, the carbon content in the produced molten metal increases, so It is preferable to use voltage operation and increase the distance between the graphite electrode and the charging material to prevent carbon pickup from the graphite electrode as much as possible.

When charging these raw materials into the arc melting furnace, the chromium oxide, the reducing agent, and the CaO-based flux may be uniformly mixed before charging. There is a lot of contact between the molten metal and the graphite electrode. Therefore, in order to prevent carbon pickup from the graphite electrode, a reducing agent is laid on the hearth, and the reducing agent and the graphite electrode are energized. The graphite electrode, and
A mixture of chromium oxide and CaO-based flux is charged so as to cover the reducing agent and the graphite electrode, and a reducing reaction occurs below the graphite electrode so that the generated molten metal and the graphite electrode are separated from each other. It is preferable to avoid contact as much as possible.

A reducing agent composed of metallic silicon, ferrosilicon, and silicon chrome melted by heating by electric current reacts with a chromium oxide composed of chromium oxide and chromite to form Si.
Reduction with silicon proceeds while generating O _2, and a metal melt containing 85% or more of chromium is generated in the arc melting furnace. Moreover, the chromium oxide reacts with the CaO-based flux due to the electric heating to lower the melting point of the chromium oxide, thereby promoting the reduction reaction of the chromium oxide with silicon. And
SiO ₂ generated by the reduction reaction reacts with CaO-based flux and chromium oxide to form molten slag (also referred to as “primary slag”), and the molten metal is covered with this molten slag.

In the silicon reduction method, silicon in the molten metal and chromium oxide in the molten slag have an equilibrium relationship. That is, when the reducing agent is excessively added to increase the silicon content in the molten metal, the chromium oxide content in the molten slag decreases. However, if the silicon content in the molten metal is excessively increased, the subsequent step of removing silicon from the molten metal becomes complicated. The experience of the present inventors has confirmed that when the silicon content in the molten metal is 0.2% or more, the chromium oxide in the molten slag is sufficiently reduced. Further, it was confirmed that even if the content of silicon in the molten metal is 1.0% or more, the reduction reaction is saturated and the chromium oxide in the molten slag is not reduced so much.
Therefore, the content of silicon in the molten metal after the reduction reaction with silicon is 0.2 to 1.0%, that is, the content of silicon after the reduction of silicon is 0.2 to 1.0%, It is preferable to determine the compounding amount of the reducing agent composed of metallic silicon, ferrosilicon, and silicochrome so as to be 0.4 to 0.8%. It has been confirmed that the reduction yield due to this silicon reduction is a high yield comparable to that of the aluminum thermite method.

It is not necessary to charge the reducing agent into the arc melting furnace at the same time as the chromium oxide, but the chromium oxide is melted in advance in the arc melting furnace, and then the reducing agent is added to the arc melting furnace to add silicon. It may be used as a method of reduction.

In this way, the silicon reduction of the chromium oxide is performed, and the silicon reduction of the chromium oxide is completed. The end time of this reduction reaction may be determined by taking a sample for analysis from the molten metal or molten slag (primary slag) and determining it from the chromium analysis value of the molten metal or molten slag. You can decide from experience.

Next, the arc melting furnace is tilted to discharge the molten slag. It is not necessary to completely discharge the molten slag (primary slag) generated by silicon reduction, and 50% or more of the generated primary slag may be discharged. However, when the amount of the primary slag remaining in the arc melting furnace is large, the amount of the basic flux to be added next is large, so it is preferable to discharge as much as possible.

Since the primary slag contains a few percent of chromium in the oxide form, the chromium yield will be lost if it is not recovered. Therefore, add metallic silicon, ferrosilicon or silicochrome into the discharged primary slag,
It is preferable to reduce the chromium oxide remaining in the primary slag and recover it as silicochrome. The recovered silicochrome can be used in place of the above reducing agent as a reducing agent for chromium oxide in an arc melting furnace.

The present inventors have confirmed that the slag does not weather if the basicity is 1.5 or less. Therefore, when the cooled primary slag is used as a roadbed material or the like, The basicity of the primary slag is set to a range of 1.3 to 1.7 when the reducing agent is added to the primary slag to recover chromium, and 1.3 when the chromium recovery of the primary slag is not performed.
It is preferably in the range of 1.5. When chromium is recovered, the basicity of 1.7 is finally reduced to 1.5 or less by reduction with silicon.

After discharging the primary slag from the arc melting furnace, a basic flux is added to the arc melting furnace. The basic flux may be any as long as it contains a basic component such as CaO or MgO as a main component, but for desulfurization of the molten metal, a flux containing CaO as a main component, for example, CaO-CaF ₂ system. Etc. are preferred.

After adding the basic flux, the current is re-energized to melt the basic flux, and the primary slag remaining in the furnace is fused with the basic flux to newly add high basicity slag ("secondary slag"). (Also referred to as)) is formed, and the secondary slag is brought into contact with the molten metal for refining. When the secondary slag to which the basic flux is added and the molten metal come into contact with each other, a reaction between silicon and oxygen occurs in the molten metal, and SiO ₂ is generated to remove silicon in the molten metal, that is, desiliconization. Processing is performed. Due to the reaction at this time, part of the chromium in the molten metal is also oxidized and transferred to the slag. still,
When oxygen remains in the form of Al ₂ O ₃ or SiO _{2 in} the secondary slag, carbon of the electrode reduces Al ₂ O ₃ or SiO ₂ and aluminum and silicon enter as impurities in the molten metal. In order to prevent this, it is preferable to discharge as much primary slag as possible.

In the secondary slag produced by adding the basic flux as described above, Si generated by desiliconization treatment is used.
O ₂ reduces the basicity of the slag. In this case, for desulfurization of the molten metal, it is desirable that the basicity of the slag after the desiliconization treatment is 2.0 or more. Therefore, the basicity of the slag after the desiliconization treatment should be 2.0. It is preferable to determine the addition amount of the basic flux. The upper limit of the basicity is not particularly limited, but the desulfurization ability is saturated even if the basicity exceeds 10.0, so the upper limit may be set to about 10.0 or less.

When the silicidation treatment of the molten metal with the secondary slag is completed, the energization is stopped and the molten metal and the secondary slag are discharged into a holding container such as a ladle. The determination of the desiliconization treatment can be reliably performed by collecting an analysis sample from the molten metal and determining from the silicon analysis value of the molten metal. Further, it is possible to determine the end of the reaction from the analysis of the secondary slag. When the amount of secondary slag is large, only the secondary slag is tapped first, and then the molten metal is tapped. The molten metal discharged is cast from a holding container into a cast iron mold or the like.
In addition, since the freezing point of metallic chromium is 1890 ° C. and the ferrochrome containing 85% or more of chromium also has a high melting point, the primary slag or the secondary slag recovered during the previous production is stored in the mold in order to protect the mold. It is preferable to spread a crushed product of the next slag or a crushed product such as magnesia. When the casting can be performed directly from the arc melting furnace into the mold, it is not necessary to once discharge the molten metal into the holding container, and the discharged molten metal can be directly cast into the mold.

The secondary slag also contains a few% of chromium in the form of oxide, and the secondary slag has a high basicity and may be weathered if left as it is. Therefore, the secondary slag is recovered. By charging the recovered secondary slag together with a raw material such as chromium oxide into an arc melting furnace to reduce silicon, the chromium yield is improved and the amount of quicklime added can be reduced. In addition, a minute amount of carbonaceous material such as coke may be added during the refining process to adjust the balance between the carbon content and the oxygen content before the vacuum heat treatment described later.

After casting, the cooled ingot is taken out of the mold, and the slag adhering to the surface of the ingot is first blasted off by shot blasting or the like. Then, using several kinds of crushers, it is crushed to a size that passes through a sieve mesh of about 50 mm.
The chromium-containing metal thus obtained has an aluminum content of 0.005% or less, a silicon content of 0.1% or less,
Although the sulfur content is 0.002% or less, it cannot be said that the oxygen content and nitrogen content are slightly high as a high-purity product, so these gas components are removed by vacuum heat treatment using vacuum treatment equipment. To do.

As the vacuum processing equipment to be used, if the pressure in the vacuum tank is 133 Pa (1 torr) or less and the charge in the vacuum tank can be raised to a temperature of 1200 ° C. or more, Any type of vacuum processing equipment can be used.

The crushed chromium-containing metal is charged into the vacuum chamber, the pressure is reduced, and heating is started in the reduced pressure state. And 13
Hold at a temperature of 3 Pa or lower and 1200 ° C. or higher for a predetermined time. By this vacuum heat treatment, in the chromium-containing metal,
Oxygen and carbon react with each other to be removed as CO gas, nitrogen is also removed as N ₂ gas, and the nitrogen content is 0.
It becomes 005% or less. The pressure, temperature, and holding time in the vacuum tank in the vacuum heat treatment cannot be unconditionally limited because they vary depending on the combination of these three factors and the specifications of the vacuum processing equipment. Is 7 Pa (0.05 torr) or less, temperature is 1350 ° C.,
It has been confirmed that a chromium-containing metal having a desired component can be produced under the condition that the holding time is 50 hours. After the vacuum heat treatment, the chromium-containing metal is prevented from oxidizing by cooling in a vacuum chamber to a temperature at which air oxidation is not performed. After cooling, the product is crushed into smaller pieces if necessary. Further, it is desirable to use a crushed chromium-containing metal in order to improve the efficiency of degassing by vacuum heat treatment and to improve the uniformity of degassing. If necessary, a carbon material such as carbon powder is added as a reducing agent to the crushed chromium-containing metal, and a lumping agent (caking agent) is further added, and the mixture is kneaded into a briquette shape,
It is more preferable to perform the vacuum heat treatment.

By producing a chromium-containing metal containing 85% or more of chromium in this manner, impurity elements such as aluminum, sulfur, silicon, carbon, oxygen and nitrogen, especially the conventional aluminum thermite method and silicon reduction method can be used. , And a chromium-containing metal containing a small amount of aluminum, silicon, and sulfur, which could not be produced by the electrolytic reduction method, can be produced efficiently, inexpensively, and stably.

Since phosphorus and iron in the chromium-containing metal produced (no problem in the case of ferrochrome having a high iron content) are brought from chromium oxide, metallic silicon and quick lime used as raw materials, As these raw materials, it is preferable to select those containing less phosphorus and iron.

Next, another embodiment of the present invention will be described. In the above embodiment, the primary step of reducing the chromium oxide with silicon in the melting furnace to obtain the molten metal and the slag generated in this primary step are discharged from the melting furnace, and then the basic flux is newly added to the melting furnace. And a secondary step of refining the molten metal by adding to the above. However, instead of chromium oxide, it contains 85% by mass or more of chromium and has an aluminum content of 0.00
5 mass% or more, silicon content of 0.1 mass% or more, and sulfur content of 0.002 mass% or more are used as a raw material, and a basic flux is newly added to this raw material to perform arc melting. It may be melted and refined in the furnace. That is, the chromium-containing metal containing impurities produced by the aluminum thermite method or the silicon reduction method may be used as a raw material, and CaO-based flux, fluorite, or the like may be added to the raw material, and only the secondary step scouring may be performed. By this manufacturing method, a chromium-containing metal having a low aluminum content of 0.005 mass% or less, a silicon content of 0.1 mass% or less, and a sulfur content of 0.002 mass% or less can be obtained.

The present invention is not limited to the above embodiments and may be implemented in various forms. The present invention is also applicable when producing ferrochrome having a chromium content of less than 85%. As the melting furnace, a high frequency melting furnace other than the arc melting furnace, a low frequency melting furnace, a resistance furnace, a plasma melting furnace, or the like may be used. In addition, a multi-stage smelting method such as a three-stage smelting method in which the molten metal is refined with a basic flux in the secondary step, the slag is discharged, and the molten metal is further refined with the basic flux in the tertiary step. Alchemy can also be adopted. This further reduces the amount of silicon and the amount of oxygen.

[0051]

[Example 1] The melting furnace body is a cassette type 4000 k.
An example of producing metallic chromium in a VA three-phase AC arc melting furnace will be described. This arc melting furnace has a structure in which only the melting furnace body can be tilted.

1350 kg of lump-shaped metal silicon sized to 20 mm or less was laid on the hearth of the melting furnace body, and a graphite electrode was placed in contact with the metal silicon. Chrome oxide and 20mm
A mixture prepared by previously mixing 4500 kg of granulated quicklime that had been sized below was charged. Then, the electrodes were energized to start heating. When the charging level in the melting furnace was lowered by heating and melting, the mixture of chromium oxide and quicklime was melted while being additionally charged, and the silicon reduction was completed in about 4 hours and 30 minutes. The basicity of the primary slag at the end of silicon reduction was set to 1.55.

The melting furnace body was tilted to discharge the primary slag. The basicity of the discharged primary slag was 1.55 as targeted, and the chromium content in the slag was 4.5%. Metallic silicon was added to this primary slag to recover silicochrome. The primary slag after recovery of silicochrome has a basicity of 1.
And the chromium content was 0.8%. The primary slag was used as a roadbed material, but it did not weather. The silicon content in the molten metal at the time of discharging the primary slag was 0.40 from the analysis result of the sample collected from the molten metal.
It was confirmed to be%.

After discharging the primary slag, 600 kg of quick lime and 300 kg of fluorite as basic flux were charged into the melting furnace and re-energized to dissolve the quick lime and fluorite to form a secondary slag. The molten metal was refined with the next slag. About 1 hour and 30 minutes after the start of re-energization, the refining was completed, the melting furnace body was tilted while the power was cut off, and the secondary slag was tapped into the cast iron mold with the primary slag spread inside. Cast. The temperature of molten metal at the time of tapping is 2000 ° C
The basicity of the secondary slag at the time of tapping was 3.5, and the chromium content in the secondary slag was 4.0%. The yield of chromium was 87% in the primary process and 85% in the secondary process. When metallic silicon was added to the slag to recover the unrecovered chromium oxide, a total yield of 95% was obtained.

After cooling, the slag adhering to the surface was removed by shot blasting. Ingot weight after blasting is about 3000
It was kg. The electric power consumption rate calculated from the weight of the ingot is 3500 kWh / t in the silicon reduction step and 1500 kWh / t in the refining step using the basic flux.
The total was 5000 kWh / t. The component analysis values of the obtained ingot are shown in Table 1. As shown in Table 1, metallic chromium having a silicon content of 0.02%, an aluminum content of 0.001% and a sulfur content of 0.0002% was obtained.

[0056]

[Table 1]

The ingot of metallic chromium was crushed to 40 mm or less by three types of crushers and charged into a vacuum heating furnace using a graphite heating element. The pressure in the vacuum chamber is 13 Pa (0.1 torr)
r) The temperature was raised to 1350 ° C. while keeping the temperature below 1350.
Hold at 50 ° C. for 50 hours. During this holding period, the pressure in the vacuum chamber was 7 Pa (0.05 torr) or less. Then, the pressure in the vacuum chamber was cooled to 13 Pa or less, and the vacuum chamber was opened to the atmosphere when cooled to room temperature. Then, an analysis sample was taken from the metallic chromium and the component analysis was performed. The analysis results are also shown in Table 1 above.

As is clear from Table 1, carbon, oxygen, and nitrogen were removed by the vacuum heat treatment, and metallic chromium of extremely high purity could be obtained. The iron content in the metallic chromium in this example is due to metallic silicon of the reducing agent, and the iron content can be reduced by using metallic silicon of high purity.

Further, 300 kg of ingot of metal chromium was crushed to 0.5 mm or less by a rod mill, and carbon powder was blended with it in an atomic ratio of 0.9 to oxygen in metal chromium. 3% of a 10% PVA solution was mixed as a lumping agent, compression molded into a briquette, and then dried. The obtained briquette was heated at 1350 ° C. under 13 Pa (0.1 Tor
It was held at r) for 50 hours and subjected to vacuum heat treatment. The analysis results are shown in Table 2.

[0060]

[Table 2]

[0061]

Example 2 Crude metal 27 produced by aluminum thermite method
Into the arc melting furnace, a mixed raw material containing 12 kg of quick lime and 12 kg of fluorspar as a basic flux and 12 kg of basic flux was charged. Then, the electrode was energized and melted to refine the crude metal. The content of aluminum, silicon, and sulfur of the crude metal by scouring is shown in Table 3.
It was reduced as shown in.

[0062]

[Table 3]

[0063]

According to the present invention, a high-purity chromium-containing metal containing less aluminum, silicon, and sulfur, which cannot be produced by the conventional aluminum thermite method, silicon reduction method, and electrolytic reduction method, is used. It can be manufactured economically and efficiently, and has industrially beneficial effects.

Continued front page    (72) Inventor Chifumi Matsumura             2-9-38 Shonishimachi, Shinminato City, Toyama Prefecture             KE Material Co., Ltd. (72) Inventor Soto Kawaguchi             2-9-38 Shonishimachi, Shinminato City, Toyama Prefecture             KE Material Co., Ltd. (72) Inventor Masanori Kato             2-9-38 Shonishimachi, Shinminato City, Toyama Prefecture             KE Material Co., Ltd. F term (reference) 4K014 CA04 CB01 CB05 CC07

Claims (10)

[Claims] 1. A primary step of reducing chromium oxide with silicon to obtain a molten metal, and a secondary step of discharging a slag produced in the primary step and then adding a basic flux to scouring the molten metal. A method for producing a chromium-containing metal, comprising: 2. A chromium oxide heated and melted in an arc melting furnace is reduced with silicon to obtain a metal melt containing 85 mass% or more of chromium, and then the slag generated by the silicon reduction is arc melted. After discharging from the furnace and discharging the slag, a new basic flux is added into the arc melting furnace, the basic flux is melted by the arc, and the slag generated by melting the basic flux and the metal melt A method for producing a chromium-containing metal, comprising: refining a molten metal by contacting with, and then casting the molten metal from an arc melting furnace. 3. The method for producing a chromium-containing metal according to claim 1, wherein the basic flux contains CaO as a main component. 4. The method for producing a chromium-containing metal according to claim 2, wherein the cast chromium-containing metal is crushed and the crushed chromium-containing metal is subjected to a vacuum heat treatment. 5. The production of a chromium-containing metal according to claim 2, wherein the cast chromium-containing metal is crushed, shaped into a briquette, and then this molded product is subjected to vacuum heat treatment. Method. 6. A chromium-containing metal produced in an arc melting furnace, containing 85 mass% or more of chromium, an aluminum content of 0.005 mass% or less, and a silicon content of 0.1 mass% or less. And a chromium-containing metal having a sulfur content of 0.002 mass% or less. 7. A chromium-containing metal produced by a combination of an arc melting furnace and vacuum processing equipment, wherein the chromium content is 8%.
Contains 5% by mass or more and has an aluminum content of 0.005
A chromium-containing metal having a mass% or less, a silicon content of 0.1 mass% or less, a sulfur content of 0.002 mass% or less, and a nitrogen content of 0.005 mass% or less. 8. The chromium-containing metal according to claim 6 or 7, wherein the chromium-containing metal is produced by reducing chromium oxide with silicon. 9. A chromium content of 85 mass% or more, an aluminum content of 0.005 mass% or more, a silicon content of 0.1 mass% or more, or a sulfur content of 0.0.
A method for producing a chromium-containing metal, comprising using a chromium-containing metal in an amount of 02 mass% or more as a raw material, adding a basic flux to the raw material, and melting and refining in a melting furnace. 10. A chromium content of 85 mass% or more, an aluminum content of 0.005 mass% or more, a silicon content of 0.1 mass% or more, or a sulfur content of 0.1.
It is a chromium-containing metal produced by using a chromium-containing metal of 002 mass% or more as a raw material, adding a basic flux to this raw material, and melting and refining in a melting furnace. A chromium-containing metal containing the above, wherein the aluminum content is 0.005 mass% or less, the silicon content is 0.1 mass% or less, and the sulfur content is 0.002 mass% or less.