JPH0369978B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> This invention is applicable to boron-11 (
¹¹ B) Concerns ¹¹ B concentrated ferroboron to be added to melting and scouring when manufacturing high-content steel materials, etc. <Prior Art> Boron is added to steel materials for purposes such as improving creep rupture strength and hardenability. This boron is natural boron and has an atomic weight of 10.
Boron-11 ( ¹⁰ B) is about 19.6% and has an atomic weight of 11.
Contains approximately 80.4% of ¹¹ B). When a material containing natural boron is irradiated with neutrons, ¹⁰ B of the boron in the material undergoes an (n, α) reaction with the neutrons to produce helium (He). This He is the main cause of deterioration of the mechanical properties of materials, such as a decrease in high-temperature ductility and creep rupture strength. Therefore, there is a need to develop nuclear reactor constituent materials that contain a boron component with a higher proportion of ¹¹ B than natural boron and can avoid the generation of He by ¹⁰ B. However, until now, a suitable enriched ¹¹ B compound has not been produced to serve as the raw material boron component necessary for the industrial production of these reactor constituent materials. A method for concentrating ¹¹ B more than natural boron is to precipitate boric acid from boron raw materials such as sodium borate, calcium borate, or crude boron, purify it by recrystallization, and then convert it to ¹⁰ B.
¹¹ There is a method that takes advantage of the difference in the weight of B, or a method that makes boron halide from boric acid and takes advantage of the difference in its chemical properties. ¹¹ B in those ways
The concentrated halide is converted into metallic boron by direct metal reduction, molten salt electrolysis, or hydrogen reduction. The method of adding ^11B to steel materials is to directly add boric acid or metallic boron during melting and smelting of steel materials, but the method of adding boric acid has poor wettability with molten steel. Because of its small specific gravity and its ability to float easily, etc.
¹¹ The yield of B is low and it is extremely difficult to add the appropriate amount. On the other hand, the method of adding metallic boron to molten steel also has the disadvantage that the specific gravity is small and it tends to float, and the production of metallic boron is complicated, resulting in high production costs and impairing the economic efficiency of the material. JP-A No. 59-232250 describes high-purity ferroboron that can be suitably used as a raw material for amorphous alloys and other applications requiring high purity, including B: 10% or more, C: 0.5% or more, in terms of weight ratio.
Ferroboron containing Al: 0.05% or less has been proposed. However, this ferroboron has a different application from that of the present invention, and does not take into account the ^proportion of ¹¹ B in B at all. It cannot be expected to avoid generation. <Problems to be solved by the invention> Therefore, the purpose of this invention is to solve the problem of (n, α) between ¹⁰ B in the material and neutrons even under a neutron irradiation environment.
Steel materials that generate little or no He during reactions, and steel that can maintain creep strength in non-radiation air, high-temperature ductility, etc. even under neutron irradiation, improved by adding ¹¹ B. The object of the present invention is to provide a raw steel raw material that can quickly, effectively, and economically add an optimum amount of ¹¹ B to the material when producing the material. <Means for Solving the Problems> According to the present invention, boron is contained in an amount of 5 to 30% (weight %, the same applies hereinafter), carbon or aluminum in an amount that inevitably remains during scouring, and the balance is iron, Ferroboron is provided which contains 90% or more of ¹¹ B based on the total amount of boron and has a melting point of 1650° C. or less. By adding ^{the 11} B-enriched ferroboron of the present invention to molten steel during the melting and refining process during the production of steel materials, steel materials with a high ¹¹ B content can be obtained efficiently and economically. The steel material thus obtained has a total boron content ( ¹⁰ B
Due to the high ratio of ¹¹ B to ¹¹ B), it is possible to reduce the generation of He due to the reaction between neutrons and ¹⁰ B in the material even in a neutron irradiation environment, and maintain good creep strength and high-temperature ductility. can. Furthermore, when adding the ferroboron of the present invention to molten steel, it melts in a short time after addition, and since the specific gravity is substantially equal to the specific gravity of the molten steel, the added feroboron can be melted and mixed uniformly into the molten steel without floating up. be able to. The ophine content in the ferroboron of this invention is 5
%, the desired amount of ¹¹ B in the molten steel
A large amount of ferroboron is required to contain the ferroboron, which impairs economic efficiency. On the other hand, if the boron content in ferroboron is more than 30%,
As the melting point of the resulting ferroboron increases above 1650°C, its specific gravity tends to decrease. Therefore, the boron content in ferroboron is 30% or less,
Preferably it is 25% or less. When the melting point of ferroboron is higher than 1650℃, it becomes difficult for the ferroboron added to molten steel to dissolve and mix uniformly in a short time, and when the specific gravity of ferroboron becomes low, the ferroboron added to the molten steel floats up and enters the steel material. ¹¹ This is not preferable because the addition yield of B decreases. As mentioned above, when the boron content in ferroboron is increased to more than 30%, the melting point tends to become higher than 1650℃, but in this case, by further adding a third element such as nickel, the final It is also possible to adjust the melting point of ferroboron to below 1650°C. In addition, the ratio of ¹¹ B to the total boron content of the ferroboron of this invention [ ¹¹ B/( ¹⁰ B + ¹¹ B)] is 90
%, the effect of reducing ¹⁰ B in the steel material obtained by adding this ferroboron and suppressing the amount of He generated in a neutron irradiation environment is small, and the economic merits of making ¹¹ B enriched ferroboron are small. disappears. When producing the ferroboron of the present invention, there is a method of melting and scouring a ¹¹ B concentrated boron compound, for example, boric acid and an iron component together with raw materials necessary for scouring in an electric furnace such as a high-frequency heating furnace;
¹¹ B Concentrated boric acid and iron component are combined with aluminum (Al)
Thermite method, which heats the powder together with the powder at a high temperature, can be used. In the former electric furnace method, carbon etc. are used to reduce the boron compound, so the obtained ferroboron will contain a small amount of carbon, but the carbon content can be reduced by increasing the scouring time as necessary. It can be made into low carbon ferroboron (JIS G2318) with a carbon content of 0.1% or less. In addition, since Al is used in the thermite method, the obtained ferroboron usually contains 4 to 4
It contains 5% Al, but this Al content depends on the amount of Al powder used in the raw material for producing ferroboron, and this amount can be determined by taking into account the reduction efficiency of ¹¹ B. Note that an Al content of 12% or less is allowed for low carbon ferroboron according to the above JIS standard. <Examples> The present invention will be described in further detail with reference to Examples below. Example 1 Boric acid with a value of ¹¹ B/( ¹⁰ B+ ¹¹ B) of 98%, pure iron powder, and carbon necessary for scouring were mixed in the proportions shown in the table below and melted in a high frequency heating furnace. Isotopic analysis of boron in ferroboron after melting revealed that the proportion of ¹¹ B in all boron remained at 98%. The melting point of the obtained ferroboron was 1650° C. or lower, and the specific gravity was 5 or higher. These properties are sufficient for melting in a short time and uniformly mixing when added to molten steel as a raw material for steelmaking.

[Table] The ferroboron of sample 3 obtained above is
100Kg of molten steel after degassing at the final stage of refining SUS304 steel
15g was added per portion. After ferroboron was added to molten steel, it immediately began to melt. After the ferroboron was dissolved, tapping was performed, and samples for analysis were collected during pouring. As a result of boron analysis, the total boron content was 28 ppm, and the proportion of ¹¹ B in the total boron was 95%. Example 2 15% each of iron powder and aluminum powder was added to boric anhydride with a value of ^11B /( ^10B + ^11B ) of 98%:
They were mixed at a ratio of 57:28, and this mixture was reacted by heating at 1000°C to produce ferroboron by the thermite method. ¹¹ B/( ¹⁰ B+ ¹¹ B) of this ferroboron
The value was 98%, which was no different from the value in boric anhydride, the raw material for ^11B . In this feroborone
It contained 4.2% Al and 20.3% boron. The obtained ferroboron was added in an amount of 10 g per 100 kg of molten steel after degassing the SUS304 steel at the final stage of refining.
Immediately after the ferroboron was dissolved, the steel was tapped, and samples for analysis were taken from the pouring process. As a result of boron analysis, the total boron content was 25 ppm, and the proportion of ¹¹ B in the total boron was 94%. <Effects of the invention> As can be seen from the above explanation, the advantages of this invention are
By using ¹¹ B enriched ferroboron as a raw material for steelmaking, ¹⁰ B in steel can be
¹¹ B can be added. Therefore, in the past, boron was not actively added to steel materials used in neutron irradiation environments due to concerns about the harmfulness of He produced through the reaction between neutrons and ¹⁰ B. Attempts have only been made to reduce the amount of boron in the material within an economically viable range, but if the ^11B -enriched ferroboron of this invention is used, it will be possible to avoid the deterioration of material properties due to He generation and achieve economical results. This makes it possible to add an appropriate amount of ^11B . Thus, in the steel material obtained by adding the ¹¹ B-enriched ferroboron of the present invention, the desirable interaction between the added ¹¹ B and other component elements is due to nuclear transmutation by the (n, α) reaction of ¹⁰ B. Since this does not occur, it is retained even in a neutron irradiation environment. Therefore, it has become possible to widely add ¹¹ B to steel materials used in neutron irradiation environments, and this will promote the development of materials with excellent neutron irradiation resistance. By using such materials, it is possible to improve the safety and extend the life of nuclear reactor structures.

Claims (1)

[Claims] 1 Consisting of 5 to 30% by weight of boron (B), the amount of carbon or aluminum that inevitably remains during scouring, and the balance iron, with 90% by weight of boron-11 ( ¹¹ B) based on the total boron content. or higher and the melting point is 1650℃
A ferroboron for addition to steel materials used in a neutron irradiation environment, characterized by the following: