KR102264466B1 - Neutron absorber and the manufacturing method thereof - Google Patents

Abstract

The present invention relates to a neutron absorber having excellent hot workability and neutron absorption ability by adding Gd and B to austenite-based stainless steel, and 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 Fe It provides a neutron absorber comprising:

Description

Neutron absorber and the manufacturing method thereof

The present invention relates to a neutron absorber, and more particularly, to a neutron absorber having excellent hot workability and neutron absorption ability by adding Gd and B to austenite-based stainless steel, and a method for manufacturing the same will be.

Containers for storing spent nuclear fuel require excellent mechanical properties and neutron absorption performance. The currently commercialized product is 304 stainless steel with B added, but in the case of B, when 1 wt% or more is added, it is difficult to manufacture due to the deterioration of hot workability, and must be manufactured by powder metallurgy. The disadvantage is that it is not economical.

Therefore, one solution is to develop a material by adding Gd, which has better neutron absorption capacity than B, together with B. However, in the case of Gd, because of its high bonding strength with oxygen at high temperature, the recovery rate is low when the product is produced using a general atmospheric melting furnace, and the Gd-oxide, which forms the oxide in the matrix tissue, has a particle size ( size) and may act as brittleness during hot working. Therefore, a casting method using vacuum melting is required.

In addition, when a certain amount of Gd and B are added to the base material, they combine with a specific element to form a secondary compound, so they may act as a factor inhibiting hot workability, and these secondary compounds are austenitic stainless steel as a base material. It has a phase transformation section at a temperature lower than the melting point of austenite stainless steel. Therefore, the hot working temperature of the secondary phase formed by Gd and B requires a different condition from the generally applied austenite stainless steel. Therefore, in order to manufacture the neutron absorber containing Gd and B, a hot working method different from that of austenite stainless steel is required.

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

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

An embodiment of the present invention for achieving the above-described problem of the present invention, Cr 11wt% to 13wt%, Ni 16wt% to 18wt%, Mo 2.5wt% to 3.5wt%, Mn 2.5wt% to 3.5wt%, A neutron absorber comprising 0.4 wt% to 0.6 wt% Si, 0.5 wt% to 0.9 wt% Gd, 0.7 wt% to 0.9 wt% B, and the balance being Fe is provided.

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

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

Another embodiment of the present invention for achieving the above-described object of the present invention is a neutron absorber material molten metal generating step of melting a 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 molten neutron absorber material to generate a neutron absorber molten metal; a casting step of producing a neutron absorber casting by tapping the neutron absorber molten metal into a mold; and a heat treatment step of heat-treating the neutron absorber casting.

The neutron absorber material mixture in the neutron absorber material molten metal generating step is, 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 0.7wt% to 0.9wt%.

The neutron absorber material molten metal generating step is, 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 it is a step of vacuum dissolving the neutron absorber element mixture comprising wt% to 0.6wt% and B 0.7wt% to 0.9wt%.

In the neutron absorber molten metal generating step, the Fe-Gd mother alloy to be added is characterized in that 0.5wt% of Gd and the remainder of the total neutron absorber material mixture are mixed with a composition ratio of Fe.

In the step of generating the neutron absorber molten metal, the Fe-Gd mother alloy is characterized in that the generation of Gd-oxide is suppressed by vacuum dissolution.

The neutron absorber molten metal generating step is characterized in that the neutron absorber molten metal is prepared by adding the Fe-Gd master alloy to the neutron absorber material molten metal at 1,400 ° C. to 1,600 ° C. and maintaining it for 1 to 3 minutes. .

The heat treatment step is characterized in that it is performed at 850 °C to 1,200 °C.

The method for manufacturing the neutron absorber may further include a hot rolling step of producing a neutron absorber plate by hot rolling the heat-treated neutron absorber casting under hot working conditions.

In the hot rolling step, the hot working condition is characterized in that the hot rolling temperature is maintained at 950 ℃ to 1,050 ℃ conditions.

The neutron absorber of an embodiment of the present invention having the above-described configuration and a method for manufacturing the same, by suppressing the generation of Gd-oxide acting as brittle during hot working by being generated by vacuum melting, including Gd and B, is hot worked It provides the effect of facilitating

In addition, the neutron absorber and its manufacturing method of an embodiment of the present invention include adding Gd and B to austenite-based stainless steel during the manufacture of the neutron absorber to prepare the neutron absorber by vacuum melting. Thus, while containing B, the hot workability is improved, thereby providing the effect of making it possible to easily manufacture the neutron absorber plate material by hot working.

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

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

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be embodied in several different forms, and thus is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, 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, coupled)” with another part, it is not only “directly connected” but also “indirectly connected” with another member interposed therebetween. "Including cases where In addition, when a part "includes" a certain component, this means that other components may be further provided without excluding other components unless otherwise stated.

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises" or "have" are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

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

In the present invention, since Gd used to produce a material capable of blocking neutrons has very high reactivity with oxygen, it is melted in a vacuum melting furnace to minimize reactivity with oxygen during dissolution, and during solidification of Gd and B compound In this case, a mold is used because there is a difficulty in that the hot workability decreases as the grain size increases. Casting Fe, Cr, Ni, Mo, Mn, Si, B suitable for the target composition of the alloy using a vacuum induction melting furnace, and melting all alloys except Gd at 1,400 to 1,600°C, preferably at 1,500°C Add a Fe-Gd master alloy of a certain size and hold it for 2 minutes, then tap it into the mold.

Accordingly, an 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 characterized by including Fe.

1 is a flowchart illustrating a process of a method for manufacturing a neutron absorber according to an embodiment of the present invention.

As shown in Figure 1, the neutron absorber manufacturing method of another embodiment of the present invention is a neutron absorber material molten metal generating step (S10) of melting a neutron absorber material mixture to generate a neutron absorber material mixture molten metal, Fe- in the neutron absorber material molten metal A neutron absorber molten metal generating step (S20) of adding a Gd master alloy to generate a neutron absorber molten metal, a casting step of producing a neutron absorber casting by tapping the neutron absorber molten metal with a mold (S30) and heat-treating the neutron absorber casting It is characterized in that it is configured to include a heat treatment step (S40).

In the neutron absorber material molten metal generating step (S10), the neutron absorber material mixture is, 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 0.7wt% to 0.9wt%.

The neutron absorber material molten metal generating step (S20) is, 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 dissolving a neutron absorber element mixture containing 0.4wt% to 0.6wt% Si and 0.7wt% to 0.9wt% B.

In the neutron absorber molten metal generating step (S20), the Fe-Gd mother alloy to be added is characterized in that 0.5wt% of Gd and the balance are mixed with a composition ratio of Fe based on the total weight of the neutron absorber.

In the neutron absorber molten metal generating step (S20), the Fe-Gd mother alloy is characterized in that the generation of Gd-oxide is suppressed by vacuum dissolution.

In the neutron absorber molten metal generating step, after adding the Fe-Gd master alloy to the neutron absorber material melt at 1,400 ° C. to 1,600 ° C., preferably 1,500 ° C., hold for 1 to 3 minutes, preferably 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 °C to 1,200 °C.

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

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

<Experimental example>

A characteristic test was performed with a specimen alloy, which is a casting of a neutron absorber produced 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] Specimen 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: From 0.7 to 0.9 wt%, the composition ratio of Gd is varied by 0.5 wt%, 0.7 wt%, and 0.9 wt%, and the content of all elements except Gd is the same, so that the balance has a composition ratio of Fe. Specimen alloys (alloys 1 to 3) were prepared by applying the neutron absorber manufacturing method of Examples.

After casting, the lower part of the casting was sampled to measure DTA, and after heat treatment at 850 ℃, 1,000 ℃ and 1,150 ℃, XRD measurement and glib test were performed to observe mortification and mechanical property change 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 currently listed in ASTM. According to the results of previous studies, the amount of Gd added increases because Gd combines with Fe and Ni in the form of an intermetallic compound in the alloy. As a result, ferrite may be generated, which may act as a factor in generating cracks during hot rolling.

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

To observe the phase change according to the temperature of the alloy after casting, the change in hot properties of Alloy 1, Alloy 2, and Alloy 3 was measured at a heating rate of 3°C/min up to 1,200°C. , a transformation point due to phase change was observed in the 900℃~1,000℃ section. In the case of alloy 1 (Alloy 1) in which 0.5 wt% of Gd was added, the transformation point was observed at about 980 °C, and in the case of Alloy 2 (Alloy 2) in which 0.7 wt% of Gd was added (Alloy 2), the transformation point was observed at about 980 °C and lower at about 910 °C. A 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, Gd forms an intermetallic compound with Ni, and a 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 produced, and since it is formed at a temperature of 1,200 ° C or higher, it was not shown in the DTA results.

It can be seen that some liquid is formed at 910 ° C., which is the section where the phase transformation occurs, and this increases the possibility of cracks occurring as the bonding strength of the product is lowered during hot working. It is preferable to perform hot working after maintaining the temperature of the product 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) after as-cast state and water-cooled specimen alloy after heat treatment at 850 ℃, 1,000 ℃, 1,150 ℃. In the case of Alloy 1, an austenite phase and Fe _1.1 Cr _0.9 B _0.9 phase were observed, and in the case of Alloy 2 (Alloy 2), as the content of Gd increased, Gd was an austenite stabilizing element. By forming an intermetallic compound with phosphorus Ni, a small amount of the ferrite phase was detected in the as-cast state and after heat treatment at 850 ° C. At temperatures above 1,000 ° C, the ferrite phase was observed. It didn't happen. And, as in Alloy 1, Fe _1.1 Cr _0.9 B _0.9 phase was observed as an austenite phase, and Fe ₂ O ₃ phase generated during heat treatment was observed at 1,000°C. Alloy 3 (Alloy 3) showed the same trend as Alloy 2 (Alloy 2). In the case of the as-cast specimen and the 850°C heat treated specimen, a ferrite phase was observed in Alloy 2 and Alloy 3, which indicates that the ferrite phase is segregated at the grain boundary during hot working. As a result, the hot workability may be deteriorated.

Gd forms an intermetallic compound with Ni, an austenite stabilizing element, and as the content of Gd increases, the amount of Gd-Ni intermetallic compound increases. The resulting ferrite phase is generated. However, as the heat treatment temperature increases, it can be observed that Ni dissolves evenly in the matrix structure and disappears due to phase stabilization at 1,000 °C. Therefore, the heat treatment conditions are preferably 950 °C or higher, where such a ferrite phase does not form.

8 is a graph of the glib test result of alloy 1-3 (alloy 1-3).

For evaluation of 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. The specimen alloy having a size of D10×H15 was heated at a temperature increase rate of 10° C./sec and maintained for 600 sec, and a strain rate of 20%/sec was assumed to be hot-rolled to 70%.

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

As a result of the gleeble test, it can be seen that the highest stress occurred at 850℃, and lower stress occurred at 1,000℃. High stress means high bonding strength of the matrix, and higher energy is required for hot working. However, when high energy is applied to the product, energy exceeding the allowable range can act as a crack generation factor, so it is preferable to perform hot working at a temperature near 1,000°C, where the stress is lower than in 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 some liquid phase during deformation and the bonding strength decreases. During hot working, this phenomenon acts as a factor causing alligator cracks. do.

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

Figure 9 shows the tensile strength and yield strength of alloy 1 (Alloy 1), alloy 2 (Alloy 2), and alloy 3 (Alloy 3) when heat treatment is performed at 1,000 ° C for specimen alloys (alloys 1, 2, and 3); , elongation, and impact properties.

The mechanical characteristic analysis result of FIG. 9 is 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 696 MPa and 602 MPa, the highest values were measured, and the elongation showed a tendency to decrease. And in the case of Alloy 3, which has the highest content of Gd, the tensile strength and yield strength decreased significantly, and were measured to be 602 MPa and 299 MPa, respectively. In the case of impact properties, the impact energy of alloy 1 (Alloy 1) and alloy 2 (Alloy 2) was 17.3 J and 18.6 J, and in the case of alloy 3 (Alloy 3), the lowest value was measured as 12 J.

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 specifically described 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 spirit of the present invention. Accordingly, the true technical protection scope of the present invention should be defined by the technical spirit of the appended claims.

Claims (12)

delete delete delete a neutron absorber material molten metal generating step of melting the neutron absorber material mixture to generate a molten neutron absorber material mixture;
a neutron absorber molten metal generating step of adding a Fe-Gd master alloy to the neutron absorber material molten metal to generate a neutron absorber molten metal;
a casting step of producing a neutron absorber casting by tapping the neutron absorber molten metal into a mold; and
A heat treatment step of heat-treating the neutron absorber casting; characterized in that it is configured to include,
The Fe-Gd master alloy to be added is characterized in that 0.5wt% to 0.9wt% of Gd with respect to the total neutron absorber material mixture and the balance is mixed with a composition ratio of Fe,
In the neutron absorber molten metal generation step, the Fe-Gd mother alloy is characterized in that the generation of Gd-oxide is suppressed by vacuum dissolution,
After the heat treatment step, a hot rolling step of manufacturing a neutron absorber plate material by controlling the hot working conditions to hot-roll the heat-treated neutron absorber casting to produce a neutron absorber plate; characterized in that it further comprises,
In the hot rolling step, the hot working condition is a neutron absorber manufacturing method, characterized in that the hot rolling temperature is maintained at 950 °C to 1,050 °C. 5. The method of claim 4, wherein the neutron absorber material mixture in 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 0.4wt% to 0.6wt%, and B 0.7 A method for producing a neutron absorber, comprising wt% to 0.9wt%. 5. The method of claim 4, wherein the generating of 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 the step of vacuum dissolving a neutron absorber element mixture containing wt% to 0.9wt%. delete delete The method of claim 4, wherein the generating of the neutron absorber molten metal comprises:
The method for manufacturing a neutron absorber, characterized in that the step of preparing the neutron absorber melt by adding the Fe-Gd master alloy to the neutron absorber material melt at 1,400° C. to 1,600° C. and maintaining it for 1 to 3 minutes. According to claim 4, wherein the heat treatment step,
A method for producing a neutron absorber, characterized in that it is carried out at 850 °C to 1,200 °C. delete delete

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