KR20210055121A - Neutron absorber and the manufacturing method thereof - Google Patents

Abstract

The present invention relates to a neutron absorber having outstanding hot processability and excellent neutron absorbing performance which result from addition of Gd and B to an austenite-based stainless steel. According to the present invention, provided is a neutron absorber comprising 11 wt% to 13 wt% of Cr, 16 wt% to 18 wt% of Ni, 2.5 wt% to 3.5 wt% of Mo, 2.5 wt% to 3.5 wt% of Mn, 0.4 wt% to 0.6 wt% of Si, 0.5 wt% to 0.9 wt% of Gd, 0.7 wt% to 0.9wt% of B, and a remaining wt% of Fe.

Description

The neutron absorber and the manufacturing method thereof TECHNICAL FIELD

The present invention relates to a neutron absorber, and more particularly, to a neutron absorber having excellent hot workability and excellent neutron absorbing ability by adding Gd and B to austenitic stainless steel, and a method of manufacturing the same. will be.

Containers for storing nuclear fuel after use are required to have excellent mechanical properties and neutron absorption performance. As a product currently commercially available, a material containing B added to 304 stainless steel is used, but in the case of B, when 1wt% or more is added, it is difficult to manufacture due to the problem of deterioration of hot workability, and it must be manufactured by powder metallurgy. Because of this, there is a disadvantage that it is not economical.

Therefore, one solution is to develop a material by adding Gd, which has better neutron absorption capacity than B, along with B. However, in the case of Gd, the binding power with oxygen is high at high temperatures, so when the product is produced using a general atmospheric melting furnace, the recovery rate is low, and Gd-oxide, which is an oxide in the matrix structure, has a particle size ( size) is large and may act as brittle during hot processing. Therefore, a casting method using vacuum melting is required.

In addition, Gd and B can act as a factor that hinders hot workability, because when a certain amount of Gd and B are added to the base material, they are combined with a specific element to form a secondary compound, and these secondary compounds are the base material, austenitic stainless steel. At a temperature lower than the melting point of steel (austenite stainless steel), it has a phase transformation section. Therefore, the hot working temperature of the secondary phase formed by Gd and B needs different conditions from that of austenite stainless steel that is generally applied. Therefore, in order to manufacture a neutron absorber including Gd and B, a hot working method different from austenite stainless steel is required.

Republic of Korea Patent Publication No. 10-2007-0024535 Korean Patent Registration No. 10-2015-0042203

Therefore, the technical problem to be solved of an embodiment of the present invention for solving the problems of the prior art described above is to add Gd and B to an austenitic stainless steel, and to improve hot workability. It is to provide a plate-type neutron absorber having excellent neutron absorption capacity and a method of manufacturing the same manufactured by controlling the conditions of hot working.

One embodiment of the present invention for achieving the object of the present invention described above, Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, Si 0.4wt% to 0.6wt%, Gd 0.5wt% to 0.9wt%, B 0.7wt% to 0.9wt%, and the balance provides a neutron absorber characterized in that it contains Fe.

Another embodiment of the present invention for achieving the object of the present invention described above, Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, Si 0.4wt% to 0.6wt%, Gd 0.5wt% to 0.9wt%, B 0.7wt% to 0.9wt%, and the balance provides a neutron absorber plate produced by hot rolling a neutron absorber, characterized in that it contains Fe do.

The hot rolling is characterized in that it is carried out at a temperature of 950 ℃ to 1,050 ℃.

Another embodiment of the present invention for achieving the object of the present invention described above is a neutron absorber material molten metal generating step of generating a neutron absorber material mixture molten metal by melting the neutron absorber material mixture; A neutron absorber molten metal generating step of adding an Fe-Gd master alloy to the neutron absorber molten metal to generate a neutron absorber molten metal; A casting step of tapping the molten neutron absorber into a mold to produce a neutron absorber casting; And a heat treatment step of heat-treating the neutron absorber cast.

The neutron absorber material mixture of the neutron absorber material molten metal generation step, based on the total weight of the neutron absorber, Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to It is characterized by containing 3.5wt%, Si 0.4wt% to 0.6wt% and B 0.7wt% to 0.9wt%.

The neutron absorber material molten metal generation step, based on the total weight of the neutron absorber, Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, Si 0.4 It is characterized in that the step of vacuum dissolving a neutron absorber element mixture containing wt% to 0.6 wt% and B 0.7 wt% to 0.9 wt%.

In the step of generating the neutron absorber molten metal, the Fe-Gd master alloy added is mixed with 0.5wt% of Gd and the balance of Fe with respect to the total neutron absorber material mixture.

In the step of generating the molten metal of the neutron absorber, the Fe-Gd master alloy is vacuum-dissolved, thereby suppressing the generation of Gd-oxide.

The step of generating the neutron absorber molten metal is a step of preparing the neutron absorber molten metal by adding the Fe-Gd master alloy to the molten metal of the neutron absorber material at 1,400° C. to 1,600° C. and maintaining for 1 to 3 minutes. .

The heat treatment step is characterized in that it is carried out at 850 ℃ to 1,200 ℃.

The method of manufacturing the neutron absorber further comprises a hot rolling step of manufacturing a neutron absorber plate by hot rolling the heat treated neutron absorber casting by controlling hot working conditions.

In the hot rolling step, the hot working condition is a condition for maintaining the hot rolling temperature at 950°C to 1,050°C.

The neutron absorber and its manufacturing method according to an embodiment of the present invention having the above-described configuration are hot working by suppressing the generation of Gd-oxide, which acts as brittle during hot working, by being produced by vacuum melting, including Gd and B. It provides an effect that facilitates.

In addition, the neutron absorber and its manufacturing method according to an embodiment of the present invention include preparing a neutron absorber by vacuum melting by adding Gd and B to austenitic stainless steel when manufacturing the neutron absorber. Accordingly, it is possible to improve hot workability while containing B, thereby providing an effect of making it possible to easily manufacture a neutron absorber plate material by hot working.

In addition, the neutron absorber and its manufacturing method according to an embodiment of the present invention improve hot workability by controlling the hot working conditions of the neutron absorber, thereby providing an effect of making it possible to easily manufacture a neutron absorber plate material.

1 is a flow chart showing a processing process of a method for manufacturing a neutron absorber according to an embodiment of the present invention.
Figure 2 is a Schaeffler diagram of the specimen alloys.
3 is a graph of the results of DTA analysis of the specimen alloys.
4 is a Gd-Ni phase diagram.
5 is a graph of the results of XRD analysis of alloy 1 (alloy1).
6 is a graph of the XRD analysis result of alloy 2 (alloy 2).
7 is a graph of the results of XRD analysis of alloy 3
Figure 8 is a graph of the results of the glbble test of the alloy 1-3 (alloy 1-3).
9 is a graph of the mechanical properties analysis results.

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be implemented in various different forms, and therefore is not limited to the embodiments described herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is said to be "connected (connected, contacted, bonded)" with another part, it is not only "directly connected", but also "indirectly connected" with another member in the middle. "Including the case. In addition, when a part "includes" a certain component, this means that other components may be further provided, not excluding other components, unless specifically stated to the contrary.

The terms used in the present specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof does not preclude in advance.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the present invention, in the case of Gd, which is used to manufacture a material capable of blocking neutrons, since it has very high reactivity with oxygen, it is melted in a vacuum melting furnace to minimize the reactivity with oxygen during melting, and the Gd and B compounds are In this case, a mold mold is used because there is a difficulty in lowering the hot workability as the grains increase. Cast Fe, Cr, Ni, Mo, Mn, Si, and B suitable for the target composition of the alloy using a vacuum induction furnace, and after dissolving all alloys except Gd, at 1,400 to 1,600°C, preferably at 1,500°C. After adding the Fe-Gd master alloy of a certain size, holding for 2 minutes, tap the mold into the mold.

Accordingly, one embodiment of the present invention, Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, Si 0.4wt% to 0.6wt% %, Gd 0.5wt% to 0.9wt%, B 0.7wt% to 0.9wt%, and the balance provides a neutron absorber comprising Fe.

1 is a flow chart showing a processing process of a method for manufacturing a neutron absorber according to an embodiment of the present invention.

As shown in FIG. 1, the method for manufacturing a neutron absorber according to another embodiment of the present invention includes a step of generating a neutron absorber material mixture molten metal by melting a neutron absorber material mixture (S10), and Fe- in the neutron absorber material molten metal. The neutron absorber melt generating step (S20) of generating a neutron absorber melt by adding a Gd master alloy, a casting step (S30) of tapping the neutron absorber melt into a mold mold to produce a neutron absorber cast (S30), and heat treatment of the neutron absorber casting. It characterized in that it comprises a heat treatment step (S40).

In the neutron absorber material molten metal generating step (S10), the neutron absorber material mixture is Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% with respect to the total weight of the neutron absorber material. % To 3.5wt%, Si 0.4wt% to 0.6wt%, and B 0.7wt% to 0.9wt%.

The neutron absorber material molten metal generation step (S20), based on the total weight of the neutron absorber, Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, It is characterized in that it is a step by vacuum melting a neutron absorber element mixture containing 0.4 wt% to 0.6 wt% of Si and 0.7 wt% to 0.9 wt% of B.

In the step of generating the neutron absorber molten metal (S20), the Fe-Gd master alloy added is mixed with 0.5wt% of Gd and the balance of Fe based on the total weight of the neutron absorber.

In the step of generating the neutron absorber molten metal (S20), the Fe-Gd master alloy is vacuum-dissolved, thereby suppressing the generation of Gd-oxide.

In the step of generating the neutron absorber molten metal, after adding the Fe-Gd master alloy to the molten metal of the neutron absorber material at 1,400° C. to 1,600° C., preferably 1,500° C., it is maintained for 1 to 3 minutes, preferably for 2 minutes. It is characterized in that the step of preparing the neutron absorber molten metal.

The heat treatment step (S40) is characterized in that it is performed at 850 ℃ to 1,200 ℃.

The method of manufacturing the neutron absorber may further include a hot rolling step (S50) of manufacturing a neutron absorber plate by hot rolling the heat-treated neutron absorber casting by controlling hot working conditions.

In the hot rolling step, the hot working condition may be a condition for maintaining the hot rolling temperature at 950°C to 1,050°C.

<Experimental Example>

Characteristic experiments were performed with a specimen alloy, which is a neutron absorber cast manufactured by the method for manufacturing a neutron absorber according to the present invention.

Table 1 is a table showing the composition ratio of the specimen alloys (alloys 1 to 3) started for the experiment.

[Table 1] Sample alloy composition table

As shown in Table 1, Cr: 11 to 13 wt%, Ni: 16 to 18 wt%, Mo: 2.5 to 3.5 wt%, Mn: 2.5 to 3.5 wt%, Si: 0.4 to 0.6 wt%, B: 0.5 wt%, 0.7 wt%, 0.9 wt% of the composition ratio of Gd is varied from 0.7 to 0.9 wt%, and the remainder is made equal to the content of all elements except Gd so that the composition ratio of Fe is the same. Specimen alloys (alloys 1 to 3) were prepared by applying the neutron absorber manufacturing method of the example.

After casting, DTA was measured by sampling the lower part of the casting, and after heat treatment at 850 ℃, 1,000 ℃ and 1,150 ℃, XRD measurement and Glbble test were performed to observe the change in mechanical properties at high temperature, and hot working through hot rolling. The conditions were confirmed.

2 is a Schaeffler diagram of specimen alloys.

It is an alloy composition that can maintain a more stable austenite phase than the 304B alloy listed in ASTM.According to the results of previous studies, Gd is combined in the form of an intermetallic compound with Fe, Ni in the alloy, so the amount of Gd is increased. As a result, ferrite may be generated, which may act as a factor of generating cracks during hot rolling.

3 is a graph of the results of DTA analysis of specimen alloys, and FIG. 4 is a Gd-Ni phase diagram.

In order to observe the phase change according to the temperature of the alloy after casting, the changes in hot properties of Alloy 1, Alloy 2, and Alloy 3 were measured at a heating rate of 3°C/min up to 1,200°C. , Transformation point due to phase change was observed in the 900℃~1,000℃ section. In the case of Alloy 1 with 0.5wt% Gd added, the transformation point was observed at about 980℃, and for Alloy 2 with 0.7wt% Gd added at about 980℃ and lower at about 910℃ The transformation point was observed. And in the case of Alloy 3 (Alloy 3) to which 0.9wt% of Gd was added, a transformation point was observed at 910℃. Based on the results of FIG. 3 and the data of FIG. 4, in the case of Alloy 1 (Alloy 1), Gd forms an intermetallic compound with Ni, so that the GdNi ₂ phase is observed, and as the content of Gd increases, Alloy 2 (Alloy 1). 2) for the case of GdNi _second phase (phase) and GdNi phase and it was observed on the process point GdNi _2, the alloy 3 (alloy 3) of it can be seen that the point on the process and the GdNi GdNi ₂ which is observed. In addition, in the case of B, (Fe,Cr) ₂ B is generated and the temperature is higher than 1,200°C, so it was not shown in the DTA result.

It can be seen that some liquids are formed at 910℃, which is the section in which the phase transformation occurs, and this increases the likelihood of cracking as the bonding strength of the product decreases during hot processing. It is desirable to perform hot processing after maintaining the product temperature at a temperature of 980°C or higher.

5 is an XRD analysis result graph of alloy 1 (alloy1), FIG. 6 is an XRD analysis result graph of alloy 2 (alloy 2), and FIG. 7 is an XRD analysis result graph of alloy 3 (alloy 3).

5 to 7 are XRD results of alloys 1, 2, and 3 (alloy 1,2,3) in an as-cast state and water-cooled specimen alloys after heat treatment at 850°C, 1,000°C, and 1,150°C. In the case of Alloy 1, the austenite phase and Fe _1.1 Cr _0.9 B _0.9 phase were observed, and in the case of Alloy 2, Gd was an austenite stabilizing element as the content of Gd increased. By forming an intermetallic compound with phosphorus Ni, a small amount of the ferrite phase was detected in the as-cast state and in the results after heat treatment at 850℃, and the ferrite phase was observed at temperatures above 1,000℃. Didn't. And, the same as Alloy 1, Fe _1.1 Cr _0.9 B _{0.9 phase was observed as austenite phase, and Fe 2} O ₃ phase generated during heat treatment was observed at 1,000°C. Alloy 3 showed the same tendency as Alloy 2. In the case of as-cast specimens and 850°C heat-treated specimens, a ferrite phase was observed in Alloy 2 and Alloy 3. This is because the ferrite phase is intergranular segregation during hot processing. It may act as a deterioration in hot workability.

Gd forms intermetallic compounds with Ni, an austenite stabilizing element, and as the content of Gd increases, the amount of Gd-Ni intermetallic compounds increases. The resulting ferrite phase is formed. However, since it was observed that Ni dissolves and disappears evenly in the matrix structure due to phase stabilization at 1,000° C. as the heat treatment temperature increases, the heat treatment condition is preferably 950° C. or higher in which such ferrite phase is not formed.

8 is a graph showing the results of a glbble test of alloy 1-3.

To evaluate the hot workability, alloys 1, 2, and 3 (Alloy 1,2,3) were subjected to hot compression tests at 850°C, 1,000°C, and 1,150°C, respectively. A specimen alloy having a size of D10×H15 was heated at a heating rate of 10°C/sec and maintained for 600sec, and the strain rate was 20%/sec , assuming hot rolling, and proceeded to 70%.

As a result of the experiment, the change in the Gd content did not affect the change in true stress, but as the temperature increased, the true stress value decreased from 400 MPa to 1,000°C at 850°C to about 360 MPa. , At 1,150°C, it was observed that the true strain decreased from 0.2 at about 200 MPa.

As a result of the Glbble test, it can be seen that the highest stress occurred at 850°C, and lower stress occurred at 1,000°C. High stress means high bonding strength of the matrix structure, and requires higher energy during hot processing. However, when high energy is applied to the product, since the energy above the allowable range can act as a cause of crack generation, it is preferable to perform hot working at a temperature near 1,000°C, which is less stress than the case of 850°C. In the case of 1150℃, it can be observed that the slope of the stress decreases as the deformation progresses. This is because the secondary phase in the tissue changes to a part of the liquid phase during the deformation and the bonding force decreases. This phenomenon acts as a factor that causes alligator cracks during hot processing. do.

9 is a graph showing the results of mechanical property analysis.

9 shows the tensile strength and yield strength of Alloy 1, Alloy 2, and Alloy 3 when heat-treated at 1,000°C for specimen alloys (alloys 1, 2, and 3). , Elongation and impact characteristics.

The mechanical property analysis result values of FIG. 9 are shown in Table 2 below.

[Table 2] Table of mechanical properties analysis results

As the content of Gd increased, the tensile strength and yield strength of Alloy 2 were measured at 696 MPa and 602 MPa, with the highest values being measured, and the elongation tended to decrease. In addition, in the case of Alloy 3, which has the highest Gd content, the tensile strength and yield strength decreased significantly, and were measured as 602 MPa and 299 MPa, respectively. In the case of impact characteristics, the impact energy of Alloy 1 and Alloy 2 was 17.3 J and 18.6 J, and the lowest value was measured as 12 J for Alloy 3.

Therefore, in view of the above experimental results, it is preferable to perform hot rolling at a temperature of 950°C to 1,050°C.

Although the technical idea of the present invention described above has been described in detail in the preferred embodiment, it should be noted that the above-described embodiment is for the purpose of explanation and not for the limitation thereof. In addition, those of ordinary skill in the technical field of the present invention will understand that various embodiments are possible within the scope of the technical idea of the present invention. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

Claims (12)

Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, Si 0.4wt% to 0.6wt%, Gd 0.5wt% to 0.9wt%, B 0.7wt% to 0.9wt% and the balance is a neutron absorber, characterized in that containing Fe. Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, Si 0.4wt% to 0.6wt%, Gd 0.5wt% to 0.9wt%, B A neutron absorber plate produced by hot rolling a neutron absorber, characterized in that 0.7wt% to 0.9wt% and the balance contains Fe. The method of claim 2,
The hot rolling is a neutron absorber plate, characterized in that performed at a temperature of 950 ℃ to 1,050 ℃. A neutron absorber material molten metal generating step of melting the neutron absorber material mixture to generate a neutron absorber material mixture molten metal;
A neutron absorber molten metal generating step of adding an Fe-Gd master alloy to the neutron absorber molten metal to generate a neutron absorber molten metal;
A casting step of tapping the molten neutron absorber into a mold to produce a neutron absorber casting; And
A method for manufacturing a neutron absorber, comprising: a heat treatment step of heat-treating the neutron absorber casting. The method of claim 4, wherein the neutron absorber material mixture in the step of generating the neutron absorber material molten metal comprises:
Based on the total weight of the neutron absorber, Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, Si 0.4wt% to 0.6wt% and B 0.7 A method for producing a neutron absorber comprising wt% to 0.9 wt%. The method of claim 4, wherein the step of generating the neutron absorber material molten metal,
Based on the total weight of the neutron absorber, Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, Si 0.4wt% to 0.6wt% and B 0.7 A method for producing a neutron absorber, characterized in that the step of vacuum melting a neutron absorber element mixture containing wt% to 0.9 wt%. The method of claim 4, wherein in the step of generating the neutron absorber molten metal,
The Fe-Gd master alloy to be added is a method for producing a neutron absorber, characterized in that the mixture has a composition ratio of Gd of 0.5 wt% and the balance of Fe with respect to the total neutron absorber material mixture. The method of claim 4, wherein in the step of generating the neutron absorber molten metal,
The Fe-Gd master alloy is a method of manufacturing a neutron absorber, characterized in that the generation of Gd-oxide is suppressed by vacuum melting. The method of claim 4, wherein the step of generating the neutron absorber molten metal comprises:
A method for manufacturing a neutron absorber, characterized in that the step of preparing the neutron absorber molten metal by adding the Fe-Gd master alloy to the molten metal of the neutron absorber material at 1,400° C. to 1,600° C. and holding the same for 1 to 3 minutes. The method of claim 4, wherein the heat treatment step,
Method for producing a neutron absorber, characterized in that carried out at 850 ℃ to 1,200 ℃. The method of claim 4, wherein the neutron absorber manufacturing method,
A method for manufacturing a neutron absorber, further comprising: a hot rolling step of producing a neutron absorber plate by hot rolling the heat-treated neutron absorber cast by controlling hot working conditions. The method of claim 11, wherein in the hot rolling step, the hot working conditions are,
A method for producing a neutron absorber, characterized in that the hot rolling temperature is maintained at 950°C to 1,050°C.

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