WO2014021600A1

WO2014021600A1 - Neutron absorbing material and method for preparing same

Info

Publication number: WO2014021600A1
Application number: PCT/KR2013/006810
Authority: WO
Inventors: 최용; 문병문; 손동성
Original assignee: 단국대학교 천안캠퍼스 산학협력단; 국립대학법인 울산과학기술대학교 산학협력단; 한국생산기술연구원
Priority date: 2012-07-30
Filing date: 2013-07-30
Publication date: 2014-02-06
Also published as: KR102061839B1; KR20150042203A

Abstract

Provided are a neutron absorbing material and a method for preparing same, wherein the neutron absorbing material is a steel comprising 0.1 to 2.5 wt% of Gd and/or 0.3 to 0.8 wt% of B, and further comprising 4.0 wt% or less of Mo (including 0 wt%), 6.5 wt% or less of W (including 0 wt%), 0.4 wt% or less of N (including 0 wt%), 16 to 34 wt% of Cr, 0.1 wt% or less of C (including 0 wt%),and Fe, and two phases of austenite and ferrite are admixed in the microstructure of the steel and an equivalent index value of the neutron absorbing material (PREN = Cr + 3.3(Mo + 0.5W) + 30N) reaches 30 or more. The neutron absorbing material according to the present invention has excellent strength, corrosion resistance, and processibility.

Description

Neutron Absorbing Material and Manufacturing Method Thereof

The present invention relates to a neutron absorbing material and a manufacturing method thereof, and more particularly, to a neutron absorbing material having excellent strength and corrosion resistance containing gadolium (Gd) and boron (B) having excellent neutron absorbing ability and a method for producing the same. .

Conventional techniques for neutron absorbing materials include Korean Patent No. 10-0147082, Austenitic steel having excellent odor resistance to neutron irradiation, and Aluminum composite having neutron absorbing performance and a method of manufacturing the same. Korean Patent No. 10-414958, Korean Patent No. 10-329471 concerning a neutron absorbing composite material and a method for manufacturing the same, Korean Patent Publication No. 10-2007-024535 concerning a method for absorbing neutrons by a boron-containing aluminum material Etc.

As in the prior arts, commercial neutron absorbing materials are largely classified into aluminum alloys and stainless steels, and developed, such as aluminum alloy-boron carbide (Al alloy-B ₄ C) and aluminum-boron carbide. Various materials have been developed such as cermets (Al-B Carbide Cermets), boron-aluminum alloys, aluminum-boron carbide composites, boron-steels, Ni-Cr-Mo-Gd alloys, and the like.

Cermet and composite materials containing boron carbide (Al alloy-B ₄ C) in commercial aluminum alloys have the advantage of being lightweight and easy to manufacture, but due to the characteristics of the material, the melting point of aluminum is low and the welding area is weak. And, there is a disadvantage that the corrosion resistance of the aluminum-boron carbide interface is weak.

On the other hand, commercial stainless steel is composed of ferritic, martensitic, and austenitic. Ferritic and martensitic systems have lower strength, corrosion resistance, and weldability than austenitic, and therefore, studies are underway to develop neutron absorber materials by adding materials having excellent neutron absorption ability to austenitic stainless steels.

As an example, the austenitic single-phase structure containing boron (B) has superior strength, corrosion resistance, and weldability as compared with aluminum alloy-boron carbide composites, but has a low solubility of boron for iron (Fe) and grain boundary segregation during firing. There is a difficulty in the manufacturing process due to crack generation by grain boundary segregation. That is, in the general melt casting process, there is a problem that cracking occurs due to grain boundary segregation during plastic working at about 300 ppm or more. In particular, since boron (B) reacts with neutrons to form helium gas, it is disadvantageous in comparison with gadolium (Gd) in neutron absorbing materials used for a long time. Meanwhile, gadolium (Gd) has a problem in that it is expensive in terms of price compared to boron (B).

The present invention is to propose a neutron absorbing material having a neutron absorbing ability, excellent strength and corrosion resistance, and a method of manufacturing the same by using a combination of gadolium (Gd) and boron (B) having excellent neutron absorbing ability.

However, the problem to be solved by the present invention is not limited to the above-mentioned problem, another task that is not mentioned will be clearly understood by those skilled in the art from the following description.

One aspect of the present invention in order to achieve the above object by weight, gadolium (Gd): 0.1 to 2.5% and boron (B): at least one of 0.3 to 0.8%, molybdenum (Mo) : 4.0% or less (including 0%), tungsten (W): 6.5% or less (including 0%), nitrogen (N): 0.4% or less (including 0%), chromium (Cr): 16 to 34%, carbon ( C): 0.1% or less (including 0%) and steel (Steel) further containing iron (Fe), the microstructure of the steel is a mixture of two phases of austenite and ferrite, the equivalent index (PREN = Cr + 3.3 ( A neutron absorbing material having a Mo + 0.5W) + 30N) value of 30 or more is provided.

Another aspect of the present invention, in weight percent, gadolium (Gd): 0.1 to 2.5% and boron (B): at least one of 0.3 to 0.8%, molybdenum (Mo): 4.0% or less (0% Tungsten (W): 6.5% or less (including 0%), Nitrogen (N): 0.4% or less (including 0%), Chromium (Cr): 16 to 34%, Carbon (C): 0.1% or less ( Casting steel further comprising 0%) and iron (Fe), and having an equivalent index (PREN = Cr + 3.3 (Mo + 0.5W) + 30N) of 30 or more; And forming a microstructure in which two phases of austenite and ferrite are mixed by performing a two-stage solidification heat treatment for quenching the solution by quenching the ferrite decomposition temperature.

Another aspect of the present invention, in weight percent, contains at least one of gadolium (Gd): 0.1 to 2.5% and boron (B): 0.3 to 0.8%, molybdenum (Mo): 4.0% or less (0 %), Tungsten (W): 6.5% or less (including 0%), Nitrogen (N): 0.4% or less (including 0%), Chromium (Cr): 16 ~ 34%, Carbon (C): 0.1% or less (Including 0%) and iron (Fe), and pressurized mixed alloy powder with an equivalent index (PREN = Cr + 3.3 (Mo + 0.5W) + 30N) of 30 or more at a pressure of 100 to 600 MPa Forming by; And forming a plate by sintering in a reducing or inert atmosphere to form a plate to form a microstructure in which two phases of austenite and ferrite are mixed.

However, in the formula representing the equivalent index, Cr, Mo, W, and N each mean a weight% value of these elements.

According to the present invention, it is possible to provide a neutron absorbing material having high strength and high corrosion resistance, and to suppress grain boundary segregation by a two-stage solidification heat treatment which is quenched by quenching during the production by the melt casting process. By having a microstructure of the boron compound of, or a superstructure of a supersaturated base metal and a microstructure of a nano-sized gadolium compound, a neutron absorbing material having improved machinability can be manufactured.

1 is an analysis diagram showing the distribution of the Gd component of 2.5% Gd-containing SUS ingot prepared by pressure sintering by area mapping with EPMA according to an embodiment of the present invention. FIG. 1 (a) is an SEM image, and FIG. 1 (b) is an image in which the position of Gd is represented as a spot.

Figure 2 is an analysis showing the component analysis of 2.5% Gd-containing SUS prepared by vacuum magnetic buoyancy dissolution method analyzed by EPMA according to an embodiment of the present invention. FIG. 2 (a) is an SEM image, and FIG. 2 (b) is an image in which the position of Gd is represented as a spot.

3 is a SEM image (a) of a Gd-duplex stainless steel and a distribution map of Cr (b), Ni (c), and Gd (d) that are area mapped with EDX according to an embodiment of the present invention. .

4 is an SEM image (a) of a Gd precipitate and an EDX spectrum (b) of a precipitate according to an embodiment of the present invention.

5 is a graph showing the solution heat treatment conditions according to an embodiment of the present invention.

6 is a photograph of a neutron absorbing material after hot rolling according to an embodiment of the present invention.

7 is a microstructure photograph of a neutron absorbing material according to an embodiment of the present invention.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

In addition, it is necessary to note that% which is a unit which shows content of the element used in this specification is a weight% unless there is particular notice.

Hereinafter, the neutron absorbing material of the present invention and its manufacturing method will be described in detail so that a person skilled in the art can easily carry out the present invention.

In general, gadolium (Gd) and boron (B) are excellent in neutron absorbing ability and can be added to aluminum or stainless steel to be used as neutron absorbers or shielding materials. However, if the composition of the steel used as a neutron absorber or shield and the microstructure of the steel are not properly adjusted, it is difficult to secure corrosion resistance and strength suitable for the application.

In order to solve the above problems, the present inventors maintain the neutron absorption capability provided by these elements by appropriately adding the amounts of gadolium and boron, and at the same time, reduce the amount of expensive gadolium, and use duplex stainless steel as a neutron absorbing material. It has been devised to devise a proper corrosion resistance and strength.

Thus, the neutron material of the present invention is a weight%, including at least one of gadolium (Gd): 0.1 to 2.5% and boron (B): 0.3 to 0.8%, molybdenum (Mo): 4.0% or less (0% Tungsten (W): 6.5% or less (including 0%), Nitrogen (N): 0.4% or less (including 0%), Chromium (Cr): 16 to 34%, Carbon (C): 0.1% or less ( 0%) and iron (Fe), and the equivalent index (PREN = Cr + 3.3 (Mo + 0.5W) + 30N) value may be made of steel (Steel) that satisfies 30 or more. Here, Cr, Mo, W, N in the above formula means the weight% value of these elements, respectively.

The reason for numerical limitation of each said component and the reason for adding these components are as follows.

가도륨(Gd): 0.1~2.5%Gadolium (Gd): 0.1-2.5%

When gadolium (Gd) is added at less than 0.1%, the effect of neutron absorption is not sufficiently obtained. Also, when it is more than 2.5%, the oxidative property between the atmosphere and the melt is high in a high temperature liquid molten state, which greatly reduces the flowability of the molten metal. ) To form an intermetallic compound and greatly reduce the formability can be limited to the above range.

붕소(B): 0.3~0.8%Boron (B): 0.3-0.8%

When boron is added in less than 0.3%, it is difficult to express the neutron absorbing remarkably, and in the case of more than 0.8%, boron may cause brittleness of the material, thereby making it difficult to mold in the solid state of the alloy, and thus it may be limited to the above range.

몰리브덴(Mo): 4.0%이하(0% 포함)Molybdenum (Mo): 4.0% or less (including 0%)

Molybdenum (Mo) may be added to improve the alloy surface stability, that is, corrosion resistance in harsh corrosive environments, but may not be added in a relatively harsh general environment. On the other hand, when it contains more than 4.0%, a sigma (σ) phase which is very fragile in a two-phase (duplex) alloy is formed, and thus has an adverse effect. Therefore, it is good to add at 4.0% or less (including 0%).

텅스텐(W): 6.5% 이하(0% 포함)Tungsten (W): 6.5% or less (including 0%)

Tungsten (W) is an expensive alloying element that positively affects the corrosion resistance, and when added in large amounts, it can promote the formation of intermetallic compounds, and therefore, in terms of phase stability, mechanical properties and corrosion resistance, the content of tungsten (6.5% or less) is less than 6.5% (including 0%). Is added.

질소(N): 0.4%이하(0% 포함)Nitrogen (N): 0.4% or less (including 0%)

Nitrogen is a useful element that improves the resistance to formulas, and its effect is about 30 times more than chromium. As a strong austenite stabilizing element, it is one of the most important elements in terms of corrosion resistance. When present simultaneously with molybdenum, the synergistic effect greatly improves the corrosion resistance. When the carbon content is lowered for the purpose of improving the intergranular corrosion resistance, it is possible to obtain the compensation of mechanical properties by adding nitrogen, inhibiting the formation of chromium carbide and increasing the tensile strength and the yield strength without reducing the elongation. It should be added in consideration of balance with carbon, chromium, nickel, molybdenum and tungsten, and austenite-ferrite phase ratio.It is an element that improves corrosion resistance but cannot be added indefinitely due to the limitation of solid solubility. ), And addition of more than 0.4% may cause brittleness of the material and gas defects during the manufacturing process. Therefore, it is desirable to control the content to 0.4% or less (including 0%).

크롬(Cr): 16~34% Chromium (Cr): 16-34%

It is the most important and basic element for maintaining corrosion resistance of stainless steel. 12% or more is required for the minimum corrosion resistance, but in the alloy of the present invention, since the austenite-ferrite two-phase structure must be obtained, it must contain 16% or more of chromium in consideration of the austenite / ferrite phase ratio. In addition, the more chromium is contained as an element for improving the corrosion resistance, the corrosion resistance is stronger, but in order to produce a duplex stainless steel according to the balance of nitrogen, molybdenum, tungsten, etc., preferably 34% or less.

탄소(C): 0.1%이하(0% 포함)Carbon (C): 0.1% or less (including 0%)

Carbon is preferably contained as little as possible because it improves the flowability of the molten metal during melt casting of the alloy, but has a very bad effect on corrosion resistance. Preferably, it is preferable to contain 0.05% or less, but when it exceeds 0.1%, the corrosion resistance may be extremely deteriorated.

철(Fe)Fe

Iron (Fe) occupies the most part of the components contained in stainless steel, and can comprise a remainder. However, in the conventional manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art, all of them are not specifically mentioned in the present specification.

당량지수(PREN = Cr + 3.3(Mo + 0.5W) + 30N) 값이 30 이상 Equivalence index (PREN = Cr + 3.3 (Mo + 0.5W) + 30N) has a value of 30 or more

Here, Cr, Mo, W, N means the weight% value of these elements, respectively. If the equivalent index value is less than 30, sufficient corrosion resistance cannot be secured, and the higher the equivalent index value, the higher the corrosion resistance, so no particular upper limit is set.

In addition to the above components, the neutron absorbing material of the present invention additionally contains at least one of vanadium (V): 10 times or less of carbon (C) and 10 times or less of niobium (Nb): carbon (C). It may include.

바나듐(V): 탄소(C)함량의 10배 이하, 니오브(Nb): 탄소(C)함량의 10배 이하Vanadium (V): 10 times or less of carbon (C) content, Niobium (Nb): 10 times or less of carbon (C) content

Vanadium and niobium typically contain 0.1 to 0.5% for heat treatment and high temperature phase stability. However, since the alloy reacts with carbon, which has a great influence on corrosion resistance, to form carbides, thereby suppressing the adverse effect of carbon, each is added at 10 times or less of the carbon content. However, if it is added more than that, the amount of vulnerable carbides increases and there is a fear that the corrosion resistance is rather deteriorated due to excessive carbide extraction. It is better not to add carbon when it is lower than 0.03%.

In addition to the components mentioned above, nickel (Ni): 0.4-8.0%, silicon (Si): 0.8% or less (except 0%), manganese (Mn): 1.2% or less (except 0%), phosphorus (P): 0.08% or less (including 0%), sulfur (S): 0.08% or less (including 0%) may be further included.

니켈(Ni): 0.4~8.0%Nickel (Ni): 0.4-8.0%

Nickel is an austenite stabilizing element and is a useful element that increases the overall corrosion resistance in terms of corrosion resistance, and therefore it needs to contain at least 0.4% or more. Considering the relationship with the ordinary ratio and the expensive material, it is limited to 8.0% or less.

규소(Si): 0.8%이하(0% 제외)Silicon (Si): 0.8% or less (excluding 0%)

Silicon is an element that stabilizes the ferrite structure, which has deoxidation effect during dissolution and refining, increases acid resistance and increases molten steel fluidity during casting, and decreases surface defects. Can increase, and the toughness and ductility of the steel is lowered. In view of corrosion resistance, 0.8% or less is preferable.

망간(Mn): 1.2%이하(0% 제외)Manganese (Mn): 1.2% or less (excluding 0%)

Manganese is an austenite stabilizing element that can replace expensive nickel, an element that increases the solubility of nitrogen and lowers the resistance to high temperature deformation. In order to improve the corrosion resistance by increasing the nitrogen content, an appropriate amount of manganese is an essential element. Corrosion resistance is degraded when a large amount is added, and the upper limit thereof is limited to 1.2% or less since it promotes the formation of highly brittle intermetallic phases.

인(P): 0.08%이하(0% 포함)Phosphorus (P): 0.08% or less (including 0%)

Phosphorus (P) is not artificially added for the manufacture of alloys, but it is inevitably contained in steel as it is naturally present in iron, alloy iron, and various non-ferrous metal elements used as raw materials while the alloy is industrially manufactured. Phosphorus is an element that causes brittleness of materials and deteriorates corrosion resistance, so the maximum allowable value is controlled to 0.08%. On the other hand, since no more phosphorus is contained, a lower limit is not set.

황(S): 0.08%이하(0% 포함)Sulfur (S): 0.08% or less (including 0%)

Sulfur is not artificially added for the manufacture of alloys, but it is inevitably contained in steel as trace amounts are naturally present in iron, ferroalloy, and various non-ferrous metal elements used as raw materials while the alloy is industrially manufactured. The maximum allowable value is controlled to 0.08% as it may cause cracking or deterioration of ductility after completion of the product, causing material brittleness. On the other hand, since sulfur is so good that it does not contain, a lower limit is not set.

The microstructure of the steel having the composition as described above is a mixture of two phases of austenite and ferrite, the present invention can target a duplex stainless steel having such a two-phase structure. Duplex stainless steel has a fine combination of austenite (γ) phase, which provides excellent processability, and ferrite (α) phase, which provides excellent corrosion resistance, so that the strength is at least 1.7 times higher than that of austenitic stainless steel. Excellent stress corrosion cracking resistance.

In addition, gadolium (Gd), gadolium oxide (Gd ₂ O ₃ ), boron (B) and a boron compound (e.g., FeB, FeB ₂ , CrB, CrB ₂ ) on the microstructure of the neutron absorbing material finely Precipitate present or form a complex structure with Gaborium boride (e.g. Gd ₂ B ₅ , GdB ₂ , GdB ₄ , GdB ₆ , GdB ₁₂ , GdB ₆₆ ) in nano size (100nm or less (except 0nm)) Can be.

Such materials present on the microstructure of the austenite-ferrite biphasic phase can produce an effect of enhancing strength and simultaneously neutron absorbing ability in the neutron absorbing material.

1 is an analysis diagram showing the component analysis of 2.5% Gd-containing stainless steel (SUS) ingot prepared by pressure sintering analyzed by EPMA according to an embodiment of the present invention, Figure 2 is an embodiment of the present invention It is the analysis figure which showed the component analysis of the 2.5% Gd containing SUS prepared by the vacuum magnetic buoyancy melt | dissolution method analyzed by EPMA according to the example. 1 (a) and 2 (a) show a BSE image, and FIGS. 1 (b) and 2 (b) show a Gd distribution.

It can be seen that the supersaturated Gd compounds are distributed relatively homogeneously in the upper and lower portions of the ingot.

3 shows the results of area mapping with EDX of Gd-duplex stainless steel. Cr, Ni, and Gd are uniformly distributed throughout the mother phase. 4 is a result of analyzing the components of the precipitate by EDX. Supersaturated Gd is a precipitate, such as gadolium oxide (Gd ₂ O ₃ ), present in grains and at grain boundaries.

Hereinafter, the method for producing the neutron absorbing material of the present invention described above will be described in detail by way of examples. However, the following examples are merely examples for describing the present invention in more detail, and do not limit the scope of the present invention.

[실시예] EXAMPLE

1. 용해주조법에 의한 중성자 흡수소재의 제조1. Preparation of neutron absorbing material by melt casting method

The raw material is prepared by dissolving in a melting furnace of inert atmosphere using pure iron, pure metal, iron alloy having a composition as shown in Table 1. (Standard composition range of alloy)

Table 1

element	weight%	element	weight%	element	weight%
Gd	0.1-2.5	P	0.08 or less (including 0)	W	6.5 or less (including 0)
B	0.3 ~ 0.8	S	0.08 or less (including 0)	N	0.4 or less (including 0)
C	0.1 or less (including 0)	Ni	0.4-8.0	V	C * 10 or less
Si	0.8 or less (excluding 0)	Cr	16-34	Nb	C * 10 or less
Mn	1.2 or less (excluding 0)	Mo	0.4 or less (including 0)	Fe	Balance

According to the melt casting method, the steel constituting the neutron-absorbing material is in weight percent, including at least one of gadolium (Gd): 0.1 to 2.5% and boron (B): 0.3 to 0.8%, and molybdenum. (Mo): 4.0% or less (including 0%), tungsten (W): 6.5% or less (including 0%), nitrogen (N): 0.4% or less (including 0%), chromium (Cr): 16 ~ 34% , Carbon (C): 0.1% or less (including 0%) and may further include iron (Fe).

In addition, for heat treatment and high temperature phase stability, by weight%, one or more of 10 times or less of vanadium (V): carbon (C) content and 10 times or less of niobium (Nb): carbon (C) content is further added. It may include.

In addition, nickel (Ni): 0.4-8.0%, silicon (Si): 0.8% or less (except 0%), manganese (Mn): 1.2% or less (except 0%), phosphorus (P): 0.08% or less ( 0%), sulfur (S): 0.08% or less (including 0%) may be further included.

A neutron absorbing material having a composition as shown in Table 1 above is an example, and an equivalent index (PREN) value defined as follows satisfies 30 or more.

PREN = Cr + 3.3 (Mo + 0.5 W) + 30 N

(Wherein, Cr, Mo, W, and N each represent the weight% value of these elements.)

Since the solubility of boron (B) in stainless steel (Fe-18% Cr) composition is small, about 1.35% by weight or more has a problem of making supersaturated solid solution of boron (B) and carbon (C) during solidification. In order to solve this problem, carbides are first made for the purpose of controlling carbon, and niobium (Nb) is used in an atomic ratio similar to that of carbon (C) to increase the solubility of boron (B) in iron (Fe) during solidification. Add.

That is, the solubility of boron (B) to iron (Fe) is increased by adding so that the atomic ratio of niobium (Nb) and carbon (C) is 1: 0.8 to 1: 1.2. In addition, a small amount of titanium (Ti) may be added, but in this case, the atomic ratio of titanium (Ti) and carbon (C) is 1: 0.8 to 1: 1.2.

The solubility of boron (B) during casting reaches 0.5% by weight, but after cooling, there is a problem of lowering to 0.05% by weight for reasons such as oxidation. In order to improve the solubility of boron (B), chromium (Cr), molybdenum (Mo), and vanadium (V) having a larger lattice constant than iron (Fe) are added during melting in the form of oxide or pure metal. Boron (B) and gadolium (Gd) may be initially used as raw materials in the form of borides (eg FeB, FeB ₂ , CrB, CrB ₂ ), and gadolium oxide (Gd ₂ O ₃ ). Particularly, in the case of gadolium (Gd) and boron (B), nanoparticles (100 nm or less (except 0 nm)) are added at a ratio of below their melting temperature in a ratio of these compounds (e.g., Gd ₂ B ₅ , GdB ₂ , GdB). ₄ , GdB ₆ , GdB ₁₂ , GdB ₆₆ ) can be manufactured and used.

In order to balance the solidified phase, alloying elements (Cr, Ni, Mo, Si, N, etc.) are appropriately blended based on Table 1 above. In order to suppress the inflow of impurities from the atmosphere during melting, in addition to commercial vacuum melting and melting in an inert atmosphere, buoyant melting using electromagnetic force may be applied to prevent the inflow of impurities through the ceramic crucible. High frequency may be applied for uniform mixing of alloying elements during dissolution.

In order to suppress the sigma phase (σ) phase in which ferrite is decomposed by vacancy reaction in the zone of 600 ~ 1,000 ℃ during melting after welding or welding, the solution is quenched by solution treatment around the ferrite decomposition temperature in the cooling stage after casting. However, solidification heat treatment is performed. The solution treatment can be performed in any alloy system in which a single-phase solid solution region exists on the state diagram, and can perform solution treatment of carbon strength. The solution treatment temperature refers to an operation of heating to an austenite region in an iron-carbon state diagram. An example of the solution treatment condition of this invention is shown in FIG. According to this, the temperature was raised at a constant rate during the initial 80 minutes, and then maintained at 1070 ° C. for 50 minutes, followed by rapid water quenching.

Through this solution treatment, grain boundary segregation that inhibits cracking in forging and cold working is suppressed, and superfine boron compound of nano-sized boron (B) and nano-sized boron compounds (eg FeB, FeB ₂ , CrB) , CrB ₂ ) will have a microstructure.

Subsequently, it can manufacture into a board | plate material through a rolling process. In order to improve the problem that forging and rolling are difficult due to the high concentration of gallium and boron, continuous hot rolling rolls are mounted on the continuous casting apparatus and passed through the hot rolling rolls before cooling to form a plate having a thickness of 10 or less (t). Neutron absorbing material can be prepared. The photograph of the hot rolled board | plate material was attached to FIG.

2. 분말 야금법에 의한 중성자 흡수 소재의 제조2. Preparation of neutron absorbing material by powder metallurgy

Although the neutron absorbing material manufactured by the melt casting method is capable of mass production and economical, the disadvantage is that various phases are generated during solidification due to high melting temperature and various alloying elements, and that boron and gadolium are oxidized and difficult to control. There are disadvantages, and in particular, it is difficult to accurately control the amount of gadolium and boron in the final product.

In order to solve this problem, the present invention sought to improve the powder metallurgy method.

TABLE 2

According to the powder metallurgy method, the steel constituting the neutron absorbing material is by weight, and includes at least one of gadolium (Gd): 0.1 to 2.5% and boron (B): 0.3 to 0.8%. Molybdenum (Mo): 4.0% or less (including 0%), Tungsten (W): 6.5% or less (including 0%), Nitrogen (N): 0.4% or less (including 0%), Chromium (Cr): 16 ~ 34 %, Carbon (C): 0.1% or less (including 0%) and may further include iron (Fe).

A neutron absorbing material having a composition as shown in Table 2 is an example, and an equivalent index (PREN) value defined as follows satisfies 30 or more.

PREN = Cr + 3.3 (Mo + 0.5 W) + 30 N

(Wherein, Cr, Mo, W, and N each represent the weight% value of these elements.)

The compound of gadolium (Gd) and boron (B) added to the neutron absorbing material is a compound of porous boride boride (Bd) by burning synthesis by heating the gadolium (Gd) and boron (B) in an inert atmosphere at 2500 ° C. or more ( Example: Gd ₂ B ₅ , GdB ₂ , GdB ₄ , GdB ₆ , GdB ₁₂ , GdB ₆₆ ), and the porous boride is mechanically pulverized to obtain a nano-sized powdery porous boride.

The raw material is a porous boride which is a compound of gadolium (Gd) and boron (B) of pure iron, pure metal, nano-sized (100 nm or less (excluding 0 nm)) in a powder state of micro size with the composition shown in Table 2 above. Blend powder of thorium (eg Gd ₂ B ₅ , GdB ₂ , GdB ₄ , GdB ₆ , GdB ₁₂ , GdB ₆₆ ).

In the mixing process, porous gadolium boride (eg Gd ₂ B ₅ , GdB ₂ , GdB ₄ , GdB), which is a compound of raw metal and nanoscale (less than 100 nm but less than 0 nm) of gadolium (Gd) and boron (B) ₆ , GdB ₁₂ , GdB ₆₆ ) by the mechanical alloying (mechanical alloying) to prepare a master alloy powder in which the presence of nano-sized gallium boride in the base material.

The master alloy powder in which the nano-sized gadolium boride is present is molded under pressure at a pressure of 100-600 MPa.

After the press molding, (1) heating at a temperature of 1050 to 1,150 ° C. in a reducing atmosphere or an inert atmosphere, pressurizing and sintering at a pressure of 10-20 MPa, and (2) solid phase sintering at a temperature of 1,200 to 1,300 ° C. in a reducing atmosphere. Sintering or (3) It can be made into a plate by the liquid sintering method of sintering at a temperature of 1,350 ~ 1,420 ℃ in a reducing atmosphere.

3. 특징3. Features

(1) Characteristics of microstructure

The microstructures are characterized by the presence of gadolium (Gd), gadolium oxide (Gd ₂ O ₃ ), boron (B) and boron compounds (e.g. FeB, FeB ₂ , CrB, A complex structure in which CrB ₂ ) is finely precipitated or distributed in a second phase, or in an austenitic-ferritic composite stainless alloy, gadolium (Gd), gadolium oxide (Gd ₂ O ₃ ), boron (B), and boron Compound boron (eg FeB, FeB ₂ , CrB, CrB ₂ ) is a complex structure in which a fine precipitate or second phase is distributed, and at the same time, a compound of gadolium (Gd) and boron (B) Gd ₂ B ₅ , GdB ₂ , GdB ₄ , GdB ₆ , GdB ₁₂ , and GdB ₆₆ ) are composite tissues that exist in nanoscale (less than 100 nm (excluding 0 nm)). 7 is a photograph of the microstructure of the neutron absorbing material of the present invention observed with an optical microscope.

Particularly, when manufactured by powder metallurgy, austenite-ferritic composite stainless alloys include gadolium boride, which is a compound of gadolium (Gd) and boron (B) (e.g., Gd ₂ B ₅ , GdB ₂ , GdB ₄ , GdB ₆ , GdB ₁₂ , GdB ₆₆ ) are made of composite tissue with nanoscale (<100nm (excluding 0nm)).

In addition, when manufactured by the melt casting method, the improved machinability is achieved by having a superstructure of boron supersaturated and nanoscale fine boron compounds, or a microstructure of supersaturated superoxide and nanosize microgadal compounds. Have

(2) mechanical properties and corrosion resistance

The steel of the austenitic-ferrite composite structure has a high strength and high corrosion resistance compared to the steel of the austenitic single phase structure.

The strength can be varied according to manufacturing conditions such as work hardening and annealing heat treatment, and cast steel shows the following ranges. It has a yield strength of about 2.2 times that of commercial single phase austenitic steel and about 2 times better corrosion resistance. Moreover, its yield strength and corrosion resistance are similar to those of commercial austenitic-ferrite two phase tissue steel, but it is strengthened by using precipitation hardening and foreign material dispersion strengthening. Is improved by more than 20%.

TABLE 3

Yield strength [MPa]	Tensile Strength [MPa]	Elongation [%]	Impact Energy [J, -46]	Corrosion Resistance [6% FeCl ₂ ]	Free Machinability [%]	Crack Sensitivity [%]
> 450	> 640	> 25	> min.50	25	100	10

(3) neutron absorption and shielding ability

Containing a large amount of gadolium (Gd) and boron (B) at the same time or each can manufacture and supply a shielding agent of the desired range, and has an neutron absorption effect is superior or at least as compared to the existing neutron absorbing material.

When manufactured by powder metallurgy, austenite-ferritic composite stainless alloys may contain a mixture of gadolium (Gd) and boron (B), which is a compound of boride (e.g., Gd ₂ B ₅ , GdB ₂ , GdB ₄ , GdB ₆ , GdB ₁₂ , GdB ₆₆ ) are nano-sized (100 nm or less (except 0 nm)) and are mostly dissolved in doped boride and relatively low in oxides (eg Gd ₂ O ₃ , B ₂ O ₅ ) Compared with the material produced by the casting method, the shielding efficiency per unit volume is high.

(4) weldability

Based on Tables 1 and 2, W and Mo may be present at appropriate ratios to improve the structure control and weldability of the heat affected zone after welding.

Claims

By weight, containing at least one of gadolium (Gd): 0.1-2.5% and boron (B): 0.3-0.8%, molybdenum (Mo): 4.0% or less (including 0%), tungsten (W) : 6.5% or less (including 0%), nitrogen (N): 0.4% or less (including 0%), chromium (Cr): 16 to 34%, carbon (C): 0.1% or less (including 0%) and iron ( Steel further containing Fe),

The microstructure of the steel is a mixture of two phases of austenite and ferrite,

A neutron absorbing material that has an equivalent index (PREN) value of 30 or more defined as follows.

PREN = Cr + 3.3 (Mo + 0.5 W) + 30 N

(Wherein, Cr, Mo, W, and N each represent the weight% value of these elements.)
The method of claim 1,

The neutron absorbing material is in weight percent, neutron absorbing further comprising one or more of 10 times or less of vanadium (V): carbon (C) content and 10 times or less of niobium (Nb): carbon (C) content. Material.
The method according to claim 1 or 2,

A neutron absorbing material in which gadolium (Gd), gadolium oxide (Gd 2 O 3 ), boron (B) and a boron compound are present on the microstructure of the neutron absorbing material.
The method according to claim 1 or 2,

The neutron absorbing material is present on the microstructure of the neutron absorbing material in the size of less than 100nm (excluding 0nm).
The method of claim 2,

The atomic ratio of the niobium (Nb) and carbon (C) is 1: 0.8 to 1: 1.2, neutron absorbing material.
By weight, containing at least one of gadolium (Gd): 0.1-2.5% and boron (B): 0.3-0.8%, molybdenum (Mo): 4.0% or less (including 0%), tungsten (W) : 6.5% or less (including 0%), nitrogen (N): 0.4% or less (including 0%), chromium (Cr): 16 to 34%, carbon (C): 0.1% or less (including 0%) and iron ( Fe), and casting a steel (Steel) satisfying an equivalent index (PREN) value of 30 or more defined as follows; And

A method of manufacturing a neutron absorbing material, comprising the step of forming a microstructure in which two phases of austenite and ferrite are mixed by a two-stage solidification heat treatment that is quenched by quenching around a ferrite decomposition temperature.

PREN = Cr + 3.3 (Mo + 0.5 W) + 30 N

(Wherein, Cr, Mo, W, and N each represent the weight% value of these elements.)
The method of claim 6,

The steel is neutron absorbing, in weight percent, further comprising one or more of 10 times or less of vanadium (V): carbon (C) content and 10 times or less of niobium (Nb): carbon (C) content. Method of manufacturing the material.
The method of claim 7, wherein

The atomic ratio of niobium (Nb) and carbon (C) contained in the steel is 1: 0.8 to 1: 1.2, the method for producing a neutron absorbing material.
The method of claim 6,

In the casting of the steel, the chromium (Cr), the molybdenum (Mo) and the vanadium (V) is added during melting in the form of oxide or pure metal, neutron absorbing material manufacturing method.
By weight, containing at least one of gadolium (Gd): 0.1-2.5% and boron (B): 0.3-0.8%, molybdenum (Mo): 4.0% or less (including 0%), tungsten (W) : 6.5% or less (including 0%), nitrogen (N): 0.4% or less (including 0%), chromium (Cr): 16 to 34%, carbon (C): 0.1% or less (including 0%) and iron ( Fe) further comprising, by pressing a mixture alloy powder satisfying an equivalent index (PREN) value of 30 or more defined as follows to a pressure of 100 ~ 600MPa; And

Sintering in a reducing or inert atmosphere to form a plate material to form a microstructure in which the two phases of austenite and ferrite are mixed, neutron absorbing material manufacturing method.

PREN = Cr + 3.3 (Mo + 0.5 W) + 30 N

(Wherein, Cr, Mo, W, and N each represent the weight% value of these elements.)
The method of claim 10,

The steel is neutron absorbing, in weight percent, further comprising one or more of 10 times or less of vanadium (V): carbon (C) content and 10 times or less of niobium (Nb): carbon (C) content. Method of manufacturing the material.
The method of claim 10,

The gadolium (Gd) and the boron (B) is included in the mixed alloy powder in the form of a powder of porous gaborium boride burn-composed by heating the gadolium (Gd) and boron (B) in an inert atmosphere , Manufacturing method of neutron absorbing material.