JPS6151020B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high-purity ferroboron, and more particularly to a method for producing high-purity ferroboron with less impurities such as C and Al using an electric furnace method. Conventionally, methods for producing ferroboron have been the thermite method, in which boron compounds such as boron oxide and boric acid are reduced with aluminum powder, and the electric furnace method, in which boron compounds are reduced in an electric furnace with a carbonaceous reducing agent. However, the problem was that the thermite method had low C but high Al, and the electric furnace method had relatively low Al but high C. Table 1 shows the JIS standards for ferroboron, and Table 2 shows composition examples of products that are actually on the market.

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【table】

[Table] Boron significantly increases the hardenability of steel, improves high-temperature strength, and has high neutron absorption capacity.
Ferroboron is mainly used as a boron additive in structural steel, high-strength steel, heat-resistant alloy steel, etc.
In this case, since the amount added is relatively small, even if the ferroboron has many impurities as mentioned above,
The reality is that we have been able to overcome this problem by using different types of Ferrobon depending on the purpose. In recent years, amorphous amorphous alloys have attracted attention due to their various characteristic properties, and in particular, Fe-B-Si amorphous alloys are used as core materials for transformers because they have significantly lower iron loss than the silicon steel sheets currently in use. Since it has the potential to become an iron core material suitable for the energy-saving era, research and development of industrial production methods for amorphous alloy thin sheets are being actively conducted. Impurities in amorphous amorphous alloys, especially Al, Ti,
Even a trace amount of P, S, etc. significantly deteriorates the electromagnetic properties of the amorphous alloy, so it is necessary to keep their content extremely low. Furthermore, when producing an amorphous amorphous alloy with a high C content, there are major restrictions on other raw materials, so it is desirable that the C content be as low as possible. By the way, the ferroboron currently available on the market has a high content of these impurities as mentioned above.
Therefore, such ferroboron cannot be used as a raw material for amorphous amorphous. Therefore, it is no exaggeration to say that whether Fe--B--Si based amorphous alloys can be used as transformer core materials depends on the availability of high-purity and inexpensive ferroboron. An object of the present invention is to provide a method for producing high-purity ferroboron, which can be suitably used as a raw material for amorphous alloys and other applications requiring high purity, based on the current state of research on amorphous alloys. The gist of the present invention is as follows. In other words, a low carbon material is produced by mixing a boron source such as boron oxide or boric acid, an iron source such as electrolytic iron or silicon iron, and a reducing agent such as charcoal or low ash coal, and charging the mixture into an electric furnace to melt and reduce the mixture. In the method for producing ferroboron,
The electrode power density in the melting reduction was set to 0.5KW/
The first step of producing low carbon ferroboron with C: 1.0% or less and B: 10% or less as cm ² or less, and the low carbon ferroboron obtained in the first step with a melting point of +150
This is a method for producing high-purity ferroboron, which is characterized by comprising a second step of completely remelting in a temperature range of ~200°C, cooling to just above the melting point, and holding at that temperature. The lowest carbon content of electric furnace ferroboron currently available on the market is around 1%.
It was thought that it would be impossible to stably produce materials with lower temperatures than this using the electric furnace method, but the inventors of the present invention found that when conducting experiments by varying the operating conditions of the electric furnace, We have found that very low C can be obtained when As a result of investigating the cause, we found that the C content was related to the electrode current density of the electric furnace, so we investigated the relationship between the electrode power density and the C content in ferroboron using a 100KVA Giraud electric furnace. The results shown in 3 tables were obtained.

[Table] If the electrode power density changes, the temperature near the electrode changes, so we assumed that the above result was ultimately caused by a change in the temperature of the reaction sphere.Next, we investigated the solubility of C in ferroboron. The results shown in Table 4 were obtained. The following facts became clear from the experimental results shown in Tables 3 and 4.

[Table] (a) As the electrode power density increases, the temperature of the reaction sphere increases. (b) As the temperature of the reaction zone increases, the solubility of C in the molten ferroboron increases. As is clear from Table 4 above, the phenomenon in which the C content in ferroboron changes significantly depending on temperature even though the B and Si contents are almost the same is not observed in other ferroalloys. This is a unique phenomenon that has never been seen before, and was discovered for the first time by the present inventors. That is, Mn-based, Cr-based,
It is well known that in typical ferroalloys such as Si-based ferroalloys, increasing the Si content in the metal significantly reduces C, and this principle is used to create low-carbon products for these ferroalloys. Manufacturing is common practice. In such a case, the effect of Si on reducing C is extremely significant, and even if there was a temperature effect, the effect would be relatively small, so it was hardly a problem in the past. In contrast, in the case of ferroboron, the effect of temperature on the C content is extremely large, as described above, and is a phenomenon that cannot be imagined from conventional technical thinking. From the experimental results shown in Table 3, it was found that the electrode power density should be suppressed to 0.5 KW/cm ² or less in order to constantly maintain the C content in the molten ferroboron at 1.0% or less. Therefore, the electrode power density during melting and reduction in the first step of the present invention is
It was limited to 0.5KW/ ^cm2 or less. Next, the solubility of C in ferroboron at a constant temperature has an inverse correlation with the content of B, and as the content of B decreases, the solubility of C increases. In the present invention, the upper limit of the C content is targeted to be 1.0% in the low carbon ferroboron in the first step and 0.5% after redissolution in the second step. Therefore, in order to stably ensure C: 1.0% or less in the first step, the B content must be at least 10%, and if B is less than 10%, C is Stable
We cannot guarantee 1.0% or less. Furthermore, if the C content of ferroboron produced in the first step is high, the amount of slag produced in the second step will increase, resulting in B separated as carbide and ferroboron lost by being mixed into the slag layer. The amount of metal increases, reducing the yield of B. Therefore, in the first step, it is necessary to reduce the C content as much as possible in order to improve the yield. Therefore, in the present invention, the target components of the low carbon ferroboron produced in the first step are limited as follows. B: 10% or more C: 1.0% or less Next, the purpose and effect of the redissolution in the second step in the present invention will be explained. The purpose of the remelting step is to stably lower C and reduce Al. Al is mainly contained in the reducing agent, and its content is high, and it is not removed in the electric furnace of the first step, which is a reducing atmosphere, but the entire amount migrates into the product, so it is important to carefully select the raw materials. Even though
It is impossible to reduce it to 0.2% or less. On the other hand, in the first step of smelting ferroboron in an electric furnace, the furnace conditions are unstable and it is difficult to maintain constant operating conditions. As shown, some degree of variation is unavoidable, so it is difficult to stably lower the C content only by smelting in the electric furnace in the first step. For the above reasons, in the present invention, the low carbon ferroboron obtained in the first step is redissolved in the atmosphere. The melting furnace used for remelting is not particularly limited, but a high-frequency electric furnace, a low-frequency electric furnace, or the like, in which the molten metal circulates and has many opportunities to come into contact with the atmosphere, is preferable. The purpose of redissolving the low carbon ferroboron obtained in the first step in the atmosphere is to precipitate and separate impurities, particularly Al and C, and therefore temperature conditions are extremely important. First, the low carbon ferroboron obtained in the first step is charged into a high frequency electric furnace etc. to raise the melting point of the alloy +
Completely melts at maximum temperature of 150-200℃. As a result of this high-temperature remelting, Al contained in the impurities is oxidized to become Al ₂ O ₃ and floated away. The reason why the maximum remelting temperature was limited to melting point +150 to 200°C is as follows. That is, the higher the temperature, the greater the effect from the sole purpose of removing Al, but at the same time B, the main component, is also oxidized and the yield is reduced. Therefore
The melting point +150 to 200°C was defined as a temperature range in which Al is removed by oxidation but the yield of B is not significantly reduced.
This temperature varies depending on the B and C contents of the low carbon ferroboron, but in the case of the following low carbon ferroboron: B: 10 to 16% C: 1% or less, the temperature range is 1550 to 1750°C. Although Al among impurities is removed by the above-mentioned high-temperature remelting, C is not removed. Therefore, in the present invention, the molten metal completely remelted at the maximum temperature is cooled to just above the melting point of the alloy and held at that temperature for a certain period of time. The holding temperature just above the melting point is preferably melting point +30 to 50°C, and in the case of low carbon ferroboron with B: 10 to 16% and C: 1% or less, a temperature range of 1350 to 1600°C is suitable, and the holding time is approximately 5 minutes is enough. The purpose of cooling to just above the melting point after remelting at this maximum temperature is to precipitate and separate the contained C. In the low carbon ferroboron produced in the first step, C exists in the form of free carbon or carbides of B and Si, but as the temperature of the molten metal decreases, the solubility of this C decreases and the C is precipitated and separated. The holding time was set in order to provide the time necessary for the precipitation and separation of C, and the precipitation and separation was almost completed within a holding time of about 5 minutes, and the C was separated.
The content will be 0.5% or less. The high-purity ferroboron from which the impurities Al and C have been separated and removed by remelting in this manner is cast into a mold to become a finished product. The high purity ferroboron thus obtained had the following composition and contained extremely few impurities. That is, it contains B: 10% or more, C: 0.5% or less, Al: 0.05% or less, and the remainder consists of Fe and inevitable impurities. Examples of the first step and second step of the present invention will be described below. Example 1 Boron oxide 10.2Kg, electrolytic iron 10.8Kg, charcoal 4.0Kg,
A mixture of 0.8 kg of coke and 0.6 kg of coal was charged into a 100 KVA single-phase Giraud electric furnace, and the results shown in Table 5 were obtained by operating the furnace while varying the electrode power density.

[Table] As is clear from Table 5, even if B is 10% or more during the production of low carbon ferrobonne in the first step,
When the average power density exceeds 0.5 KW/cm ² , the C content of the primary product becomes high, making it difficult to ensure C: 1.0% or less, and the Al content is also high. Example 2 Boric acid 10.2Kg, silicon iron scrap 10.7Kg, charcoal 4.0Kg,
Pre-mix at a ratio of 1.0Kg of coal and 0.8Kg of coke,
As a result of charging this into a 100KVA single-phase Giraud electric furnace and operating it at an average electrode power density of 0.5KW/ ^cm2 ,
An excellent primary product, low carbon ferroboron, having the following composition could be obtained. B: 15-16% C: 0.3-0.7% Al: 0.02-0.19% Example 3 Six types of low carbon ferroboron test materials with different C and Al contents obtained in the primary process of Examples 1 and 2 A secondary step remelting test was carried out on 20 kg of each sample in a 30 kg high-frequency electric furnace, and the relationship between the removal rate of C and Al and the yield of B was compared. The redissolution comparative test was conducted in the following manner. That is, each low-carbon ferroboron sample material was charged into a furnace, energized to melt it completely, the temperature was further raised, and the molten metal temperature was maintained at 1700-1750°C for 5 minutes, then the temperature was lowered to 1600°C, and the temperature was lowered to 1550-1750°C.
After holding the mixture at 1600°C for 5 minutes, it was cast into a mold and allowed to cool to obtain high purity ferroboron. C, Al before and after remelting
Changes in content and yield of B are shown in Table 6. As is clear from Table 6, regarding the C content, the higher the amount of C in the low carbon ferroboron in the primary process, the better the removal rate. It shows the removal rate of B.

[Table] The yield tends to deteriorate as the C content before redissolution increases. Furthermore, although no particular tendency was observed regarding the Al content, it was found that all of them exhibited excellent removal rates of 75% or more. As described above, if the C content in the low carbon ferroboron in the first step exceeds 1.0%, the yield of B will decrease, so in the present invention, the target C content in the low carbon ferroboron in the first step is set to With emphasis on yield, C: 1.0% or less and B: 10% or more. Therefore, it has been found that a yield of B of 95% or more can be secured under these limiting conditions. Example 4 Using the same raw materials and equipment as Examples 1 and 2,
Reductive dissolution was carried out at an electrode power density of 0.4 to 0.5 KW/cm ² to obtain a primary product of low carbon ferroboron having B: 10 to 11%, C: 0.3 to 0.8%, Al: 0.07 to 0.15%. Using the same 30Kg high-frequency electric furnace as in Example 3, each test material was remelted at 1550 to 1600℃, which is the melting point +150 to 200℃, and Al was precipitated and separated.The molten metal temperature was then lowered to 1400℃. The sample was held in a temperature range of 50°C for 5 minutes to precipitate and separate C, and then cast into a mold. In this way, the final product was able to obtain an excellent high purity ferroboron with low C and Al content as shown below. B: 10 to 11% C: 0.2 to 0.4% Al: 0.01 to 0.03% As is clear from the above examples, the present invention mixes and charges a boron source, a low carbon iron source, and a reducing agent such as charcoal. In the production method of low-carbon ferroboron, which is melted and reduced in an electric furnace, the electrode power density is
By adjusting the temperature to ^below 0.5KW/cm2 and keeping the temperature of the reaction zone relatively low, C: below 1.0%, B:
A method was adopted in which primary low carbon ferroboron with a concentration of 10% or more was produced and then this primary product was redissolved in the atmosphere. Therefore, when remelting, first raise the temperature to a maximum temperature of 150 to 200 degrees Celsius above the melting point of the alloy to completely melt the primary product and remove Al, then cool to a temperature just above the melting point and heat it to that temperature for about 5 seconds. Since we adopted a method in which C was precipitated and separated by holding for a minute, we were able to achieve the following effects. (b) C content in the primary product is reduced from 30 to 70 by re-melting treatment.
%, Al was able to be precipitated and separated with a removal rate of over 80%. (b) Within the limited scope of the present invention, B
We were able to achieve an excellent yield of over 95%. (c) According to the present invention, it is possible to obtain at a low cost high-purity ferroboron with extremely low impurities that have not been seen in the conventional market, including B: 10% or more, C: 0.5% or less, and Al: 0.05% or less.
-B-We are now able to fully meet the demand for Si-based amorphous alloys, etc.

Claims (1)

[Claims] 1. A boron source such as boron oxide or boric acid, an iron source such as electrolytic iron or silicon iron, and a reducing agent such as charcoal or low ash coal are mixed and charged into an electric furnace. In the method for producing low carbon ferroboron by melting and reducing, a ^first step of producing low carbon ferroboron with C: 1.0% or less and B: 10% or more by setting the electrode power density in the melting reduction to 0.5 KW/cm 2 or less, and the A second step of completely remelting the low carbon ferroboron obtained in the first step at a temperature range of +150 to 200°C above the melting point, cooling it to just above the melting point, and maintaining the temperature at that temperature. A method for producing high-purity ferroboron. 2. The redissolution in the second step is performed in the case of B: 10 to 16%, with a maximum temperature of 1550 to 1750°C, a holding temperature of 1350 to 1600°C, and a holding time of about 5 minutes. Method of manufacturing purity ferroboron.