A gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability and its preparation method

Abstract

The present invention discloses a gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability. Its main components are composed according to the following mass percentages (%): C ≤ 0.03, Cr: 15.0 - 25.0, Gd: 0.5 - 5.0, Ni: 20.0 - 45.0, and it satisfies 0.40 ≤ Ni / Fe mass ratio ≤ 1.8. The remaining part is iron and inevitable impurities. An alloy melt is obtained through batching and vacuum induction melting process; through casting, and then through processes such as hot forging, hot rolling, cold rolling, and annealing treatment, finally a rod or plate or tube of gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability is prepared. The gadolinium-rich iron-nickel-based alloy material of the present invention has the advantages of high strength, low cost, excellent corrosion resistance, and good processing and formability.

Description

Technical Field

[0001] The present invention relates to an iron-nickel-based alloy material and a preparation method thereof, in particular to a gadolinium-rich iron-nickel-based alloy material for nuclear shielding and a preparation method thereof, which are applied to the technical field of nuclear functional steel alloys. Background Art

[0002] As one of the three major main power energy supply pillars alongside thermal power and hydropower, nuclear energy has been widely utilized worldwide. In the core of a nuclear reactor, when the concentration of fissile isotopes drops to a level where the established power cannot be maintained, the fuel in the core becomes spent fuel and needs to be discharged. As most of the spent fuel is discharged from nuclear power plants due to the expiration of the working life, the storage capacity of the in-pool storage is approaching saturation, so the disposal problem of spent fuel has become a global challenge. The spent fuel discharged from a nuclear reactor has extremely strong radioactivity, accompanied by a certain neutron emission rate and heat release. According to the nuclear fuel closed-loop cycle mode, after the spent fuel assembly is discharged from the reactor, it is generally stored in the spent fuel pool for a certain period of time and then transported to an off-site storage facility for storage, or directly transported to a reprocessing plant for treatment and disposal. Usually, each million-kilowatt nuclear power unit can discharge 25 tons of spent fuel per year, and the global cumulative scale of spent fuel is huge. On the other hand, with the development of small mobile nuclear reactors, higher requirements are put forward for neutron shielding materials. Materials used for nuclear shielding not only need to have excellent shielding functionality but also excellent room-temperature mechanical properties and even high-temperature mechanical properties so that they can be used as structural materials. Such functional structure integrated materials can meet the needs of the increasingly developing nuclear industry. Currently, boron steel is widely used for storing reactor spent fuel. In recent years, stainless steels with a boron mass fraction of 0.6% and 1.0% have been continuously cast. They have high strength, excellent corrosion resistance, and good neutron absorption ability. However, the solubility of boron in stainless steel is low, and the addition of excessive boron will precipitate boride (Fe,Cr) 2 B, resulting in a significant reduction in hot ductility, and it is very difficult to industrially produce boron steel with a higher boron content. B 4 The C / Al neutron absorption material has problems such as complex processes, severe interfacial reactions between B 4 C and Al, corrosion resistance, radiation resistance, and aging during use. In addition, some polymer-based composite materials are used for neutron shielding, but these materials also have problems such as aging and uneven distribution, and it is difficult to use them at high temperatures. These all limit the application and development of neutron absorption materials. Therefore, the development of iron and steel-based materials still has broad application prospects in the nuclear industry.

[0003] In recent years, due to the fact that the gadolinium (Gd) element has a relatively large equivalent neutron absorption cross-section, reaching as high as 36,300 barns, approximately 4,600 barns per atom, and has good thermal stability and thermal neutron radiation stability, it has attracted the attention of many researchers. M. Copeland and H. Kato studied the corrosion resistance and mechanical properties of gadolinium-rich 304L alloys, and Lehigh University in the United States studied the corrosion resistance of 316L stainless steels with different Gd contents. However, in iron-based austenitic stainless steel alloys such as gadolinium-rich 304Gd and gadolinium-rich 316Gd, since gadolinium does not dissolve in the matrix but forms a low-melting-point compound (Fe,Cr,Ni) 3 Gd, whose melting point is around 1060 °C, which makes it very difficult to perform hot processing on the material, affecting the hot working performance and mechanical properties of the material. In addition, due to the presence of low-melting-point Gd-rich precipitates, the material does not have excellent welding properties, so it is very difficult to fabricate large components that meet the nuclear shielding requirements. The gadolinium-rich Hastelloy C-4 (00Cr16Ni66Mo16Ti + 1.58Gd), Hastelloy C-22 (00Cr21Ni57Mo13W3 + 1.98Gd), Alloy 59 (00Cr23Ni59Mo16 + 1.82Gd), etc. developed by the Idaho National Laboratory in the United States in cooperation with Lehigh University. In these alloys, Gd forms a high-melting-point compound Ni 5 Gd, whose melting point is around 1260 °C, which is very beneficial to its hot processing. However, these Ni-based alloys have a very high Mo content and high costs, which also limits their large-scale application.

[0004] Therefore, it is very meaningful to utilize the excellent thermal neutron absorption performance of Gd to prepare gadolinium-rich iron-based alloys, while enabling the precipitates of the alloy material to have a high melting point and saving costs as much as possible. The nuclear power industry urgently needs a thermoneutron shielding material with integrated structural and functional properties that has a simple production process, is easy to process, has low costs, and good plasticity and toughness. Summary of the Invention

[0005] To solve the problems of the existing technology, the purpose of the present invention is to overcome the deficiencies of the prior art and provide a gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability and its preparation method. The main function of nuclear radiation shielding materials is to absorb or attenuate neutrons and gamma rays. For neutrons, after passing through the pressure vessel and the sealed chamber, most neutrons have been slowed down to thermal neutrons or epithermal neutrons. Such neutrons require materials with a large thermal neutron absorption cross-section for effective absorption without spilling out. Therefore, the present invention develops a new low-cost, easy-to-process and weldable, non-swelling gadolinium-rich Fe-Ni-based alloy during irradiation, avoiding the problems of difficult hot working of stainless steels such as 304Gd and 316Gd and the high cost of gadolinium-rich nickel-based alloys, which has substantial significance.

[0006] To achieve the above object, the present invention adopts the following inventive concept:

[0007] Materials with elements having a large neutron capture cross-section are required for neutron shielding. The gadolinium element has the largest neutron equivalent absorption cross-section, up to 36300 barns, about 4600 barns per atom, and has good thermal stability and thermal neutron radiation stability. Gadolinium compounds do not produce harmful by-products such as deuterium like boron carbide. Gadolinium is non-toxic and there is no pollution in the manufacturing process. After gadolinium elements absorb neutrons, it will not cause swelling of the material. Through a large number of experimental studies, the present invention finds that in the FeCrNi alloy, by adjusting the ratio of Ni / Fe, the type of gadolinium-rich precipitation phase formation can be changed, that is, only high-melting-point (Ni,Cr,Fe) 5 Gd needs to be formed in the alloy, rather than low-melting-point (Fe,Cr,Ni) 3 Gd. During the vacuum induction melting process of the iron-nickel-based alloy, adding appropriate proportions of gadolinium, chromium, and molybdenum and controlling the ratio of Ni / Fe can prepare a gadolinium-rich iron-nickel-based alloy material with excellent corrosion resistance and excellent hot workability. This material is mainly composed of an austenite matrix and (Ni,Cr,Fe) 5 Gd intermetallic compounds distributed along the austenite grain boundaries. Compared with the prior art, the present invention adjusts the raw material ratio of nickel and iron, reduces the usage of Ni and Mo, appropriately increases the iron content, can provide a new type of low-molybdenum, ultra-low-molybdenum or molybdenum-free gadolinium-rich iron-nickel-based alloy material, is more conducive to the formation of a composite phase structure, significantly reduces the raw material cost, and at the same time reduces the burning loss of high-cost metal raw materials, obtains a higher material performance-price ratio, and is more suitable for industrial production applications.

[0008] According to the above inventive concept, the present invention adopts the following technical solutions:

[0009] A gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability, the main components of which are composed according to the following mass percentages (%): C ≤ 0.03, Cr: 15.0 - 25.0, Gd: 0.5 - 5.0, Ni: 20.0 - 45.0, and 0.40 ≤ Ni / Fe mass ratio ≤ 1.8, with the remaining part being iron and inevitable impurities.

[0010] As a preferred technical solution of the present invention, the composition of the gadolinium-rich iron-nickel-based alloy material further contains the Mo element, and the main components of the gadolinium-rich iron-nickel-based alloy material for nuclear shielding are composed according to the following mass percentages (%): C: 0.013 - 0.028, Cr: 15.0 - 25.0, Gd: 0.5 - 5.0, Ni: 25.0 - 45.0, Mo ≤ 8.0, with the remaining part being iron and inevitable impurities.

[0011] As a more preferred technical solution of the present invention, the main components of the gadolinium-rich iron-nickel-based alloy material are composed according to the following mass percentages (%): C: 0.013 - 0.028, Cr: 15.0 - 25.0, Gd: 0.5 - 5.0, Ni: 25.0 - 45.0, Mo: 0 - 5.0, with the remaining part being iron and inevitable impurities.

[0012] As a preferred technical solution of the present invention, the microstructure of the gadolinium-rich iron-nickel-based alloy mainly consists of austenite and high-melting-point second-phase (Ni, Cr, Fe) 5 Gd intermetallic compounds; in the gadolinium-rich iron-nickel-based alloy, the high-melting-point second-phase (Ni, Cr, Fe) 5 Gd is distributed along the austenite grain boundaries in the matrix, and the length dimension of the austenite grains is not greater than 150 μm.

[0013] As a preferred technical solution of the present invention, the room-temperature tensile fracture strength of the gadolinium-rich iron-nickel-based alloy material is not lower than 350 Mpa, and the fracture elongation is not lower than 35.0%.

[0014] As a more preferred technical solution of the present invention, the room-temperature tensile fracture strength of the gadolinium-rich iron-nickel-based alloy material is

[0015] 350 - 600 Mpa, and the fracture elongation is not lower than 35.0%.

[0016] A preparation method of the gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability according to the present invention includes the following steps:

[0017] a. Using the vacuum induction melting process, when preparing the raw material ingredients, the main raw material components are proportioned according to the following mass percentages (%) for raw material batching: C ≤ 0.03, Cr: 15.0 - 25.0, Gd: 0.5 - 5.0, Ni: 20.0 - 45.0, and it satisfies 0.40 ≤ Ni / Fe mass ratio ≤ 1.8, with the remaining part being iron and inevitable impurities; all the weighed raw materials after batching are subjected to vacuum induction melting, and the melting temperature is controlled to obtain an alloy melt;

[0018] b. Cast the alloy melt prepared in step a into a mold, and subject the cast alloy ingot to hot forging, hot rolling, cold rolling, and annealing heat treatment processes in sequence, finally obtaining a gadolinium-rich iron-nickel-based alloy material rod, sheet, or tube for nuclear shielding with excellent hot workability.

[0019] As a preferred technical solution of the present invention, in step a, the main raw material components are proportioned according to the following mass percentages (%) for raw material batching: C: 0.013 - 0.028, Cr: 15.0 - 25.0, Gd: 0.5 - 5.0, Ni: 25.0 - 45.0, Mo ≤ 8.0, and the remaining part is iron and inevitable impurities.

[0020] As a preferred technical solution of the present invention, in step a, the main raw material components are proportioned according to the following mass percentages (%) for raw material batching: C: 0.013 - 0.028, Cr: 15.0 - 25.0, Gd: 0.5 - 5.0, Ni: 25.0 - 45.0, Mo: 0 - 5.0, and the remaining part is iron and inevitable impurities.

[0021] Compared with the prior art, the present invention has the following obvious outstanding substantial features and remarkable advantages:

[0022] 1. Compared with traditional boron steel or B 4 C / Al-based composites, the neutron shielding performance of the present invention using gadolinium element is much higher than that of boron element, and the content of Gd element in the present invention is also relatively high; after casting into a mold and then undergoing processes such as hot forging, hot rolling, cold rolling, and annealing treatment, a gadolinium-rich iron-nickel-based alloy sheet, rod, or tube for nuclear shielding is finally obtained, which has excellent hot workability and the potential to manufacture large-sized sheets or tubes;

[0023] 2. Compared with the existing Gd-rich 304 and 316 alloys, the precipitated phase in the alloy of the present invention is (Ni,Cr,Fe) 5 Gd instead of the low-melting-point (Fe,Ni,Cr) 3 Gd; (Ni,Cr,Fe) 5The melting point of Gd is above 1200 °C, which means that the alloy can be hot-worked below 1200 °C, endowing the alloy with excellent hot-working properties that are not possessed by Gd-rich 304 and 316 alloys; in addition, compared with Gd-rich Ni-based alloys, by controlling the Ni / Fe ratio in the present invention, the consumption of Ni is saved, enabling the material to not only have excellent mechanical properties, good corrosion resistance and excellent processing formability, etc., but also reduce costs;

[0024] 3. After the Gd-rich Fe-Ni-based alloy material for nuclear shielding of the present invention is subjected to heat forging, hot rolling, cold rolling and annealing, etc. within its composition range, its room temperature tensile fracture strength is 350-600 Mpa, the fracture elongation rate is not less than 35.0%, and its corrosion resistance and hot-working properties are excellent; since gadolinium is the element with the largest thermal neutron capture cross section among rare earth elements, experiments show that compared with traditional boron steel or B 4 C / Al-based composites, at the same material thickness, the Gd-rich Fe-Ni-based alloy of the present invention has better shielding performance. Under the same shielding effect, the Gd-rich Fe-Ni-based alloy of the present invention can be made lighter and thinner, and it is the best candidate material to replace traditional boron steel or B 4 C / Al-based composites and other series in the future, and can also greatly reduce the raw material cost, and is a high-performance neutron shielding material;

[0025] 4. The Gd-rich Fe-Ni-based alloy material for nuclear shielding of the present invention has good compatibility, high strength, good plasticity and toughness, corrosion resistance, radiation resistance, simple production process, easy processing and low cost. The Gd-rich Ni-based alloy material of the present invention can be used for the storage and transportation of reactor spent fuel and neutron shielding environment, and the material is easy to process. Brief Description of the Drawings

[0026] Figure 1 Metallographic microstructure photograph of the alloy in Example 1 of the present invention. Detailed Description of the Invention

[0027] The above scheme will be further described below in conjunction with specific implementation examples, and the preferred implementation examples of the present invention are described in detail as follows:

[0028] Example 1:

[0029] In this example, a preparation method of a Gd-rich Fe-Ni-based alloy material for nuclear shielding includes the following steps:

[0030] a. Adopt the vacuum induction melting process. When formulating the raw materials, the raw material components are formulated according to the following mass percentages (%) for raw material batching: C: 0.02%, Cr: 20.0%, Gd: 2.5%, Ni: 35.0%, and Fe is the balance and inevitable impurities; all the weighed raw materials after batching are subjected to vacuum induction melting to obtain an alloy melt;

[0031] b. Cast the alloy melt prepared in step a into a mold, and subject the obtained alloy ingot to processes such as hot forging, hot rolling, cold rolling, and annealing heat treatment in sequence, finally obtaining a gadolinium-rich iron-nickel-based alloy plate or rod for storing reactor spent fuel.

[0032] In this embodiment, a vacuum induction melting process is adopted. During the comprehensive batching and melting process, (Ni, Cr, Fe) 5 is formed after Gd is added. After casting and forming, and then through processes such as hot forging, hot rolling, cold rolling, and annealing treatment, a gadolinium-rich iron-nickel-based alloy plate or rod for storing reactor spent fuel is finally obtained. Microscopic observation and analysis are carried out on the prepared gadolinium-rich iron-nickel-based alloy. The microstructure of the gadolinium-rich iron-nickel-based alloy mainly consists of austenite and high-melting-point second-phase (Ni, Cr, Fe) 5 Gd intermetallic compounds; the high-melting-point second-phase (Ni, Cr, Fe) 5 Gd in the matrix is distributed along the austenite grain boundaries, and the length dimension of the austenite grains is not greater than 150 μm. Through experimental tests, the test results show that the room-temperature tensile fracture strength of the gadolinium-rich iron-nickel-based alloy plate or rod prepared in this embodiment is greater than 400 MPa, and the fracture elongation is greater than 40.0%. The mechanical and corrosion resistance properties of the gadolinium-rich iron-nickel-based alloy material prepared in this embodiment are superior to those of traditional boron steel or B 4 C / Al-based composites, and can be used as plates, rods, tubes and other components for storing reactor spent fuel, etc. It is the best candidate material to replace traditional boron steel or B 4 C / Al-based composites and other series in the future, and can greatly reduce the raw material cost.

[0033] Example Two:

[0034] This embodiment is basically the same as Example One, with the special feature being:

[0035] In this embodiment, a method for preparing a gadolinium-rich iron-nickel-based alloy material for nuclear shielding includes the following steps:

[0036] a. Adopt a vacuum induction melting process. When formulating the raw materials, the raw material components are formulated according to the following mass percentages (%): C: 0.015%, Cr: 18.0%, Gd: 3.0%, Ni: 38.0%, and the balance is Fe and unavoidable impurities; subject all the weighed raw materials after batching to vacuum induction melting to obtain an alloy melt;

[0037] b. This step is the same as that in Example One.

[0038] Microscopic observation and analysis are carried out on the prepared gadolinium-rich iron-nickel-based alloy. The microstructure of the gadolinium-rich iron-nickel-based alloy mainly consists of austenite and high-melting-point second-phase (Ni, Cr, Fe) 5Gd intermetallic compound composition; high melting point second phase (Ni, Cr, Fe) in gadolinium-rich iron-nickel-based alloy 5 Gd is distributed along the austenite grain boundaries in the matrix, and the length dimension of the austenite grains is not greater than 150 μm. Through experimental tests, the test results show that the room temperature tensile fracture strength of the iron-nickel-based alloy material rod prepared in this example is greater than 450 MPa, and the fracture elongation is greater than 45.0%. The mechanical and corrosion resistance properties of the iron-nickel-based alloy material prepared in this example are superior to those of traditional boron steel or B 4 C / Al-based composite material, and can be used as components such as pipe materials or plates for nuclear shielding and other aspects. It is the best candidate material to replace traditional boron steel or B 4 C / Al-based composite material and other series, which can greatly reduce the raw material cost.

[0039] Example 3:

[0040] This example is basically the same as the previous example, and the special feature is that:

[0041] In this example, a preparation method of an iron-nickel-based alloy material for nuclear shielding includes the following steps:

[0042] a. Adopt the vacuum induction melting process. When preparing the raw material ingredients, the raw material components are prepared according to the following mass percentage (%): C: 0.023%, Cr: 25.0%, Gd: 5.0%, Ni: 45.0%, and the balance is Fe and inevitable impurities; all the weighed raw materials after batching are subjected to vacuum induction melting to obtain an alloy melt;

[0043] b. This step is the same as that in Example 1.

[0044] Microscopic observation and analysis are carried out on the prepared gadolinium-rich iron-nickel-based alloy. The gadolinium-rich iron-nickel-based alloy structure mainly consists of austenite and high melting point second phase (Ni, Cr, Fe) 5 Gd intermetallic compound composition; high melting point second phase (Ni, Cr, Fe) in gadolinium-rich iron-nickel-based alloy 5 Gd is distributed along the austenite grain boundaries in the matrix, and the length dimension of the austenite grains is not greater than 150 μm. Through experimental tests, the test results show that the room temperature tensile fracture strength of the iron-nickel-based alloy material rod prepared in this example is greater than 500 MPa, and the fracture elongation is greater than 35.0%. The mechanical and corrosion resistance properties of the iron-nickel-based alloy material prepared in this example are superior to those of traditional boron steel or B 4 C / Al-based composite material, and can be used as components such as pipe materials and plates for reactor spent fuel storage and other aspects. It is the best candidate material to replace traditional boron steel or B 4 C / Al-based composite material and other series, which can greatly reduce the raw material cost.

[0045] Example 4:

[0046] This example is basically the same as the previous examples, with the special feature being:

[0047] In this example, a preparation method of an iron-nickel-based alloy material for nuclear shielding includes the following steps:

[0048] a. Using the vacuum induction melting process, when preparing the raw material mixture, the raw material components are proportioned according to the following mass percentages (%): C: 0.025%, Cr: 15.0%, Gd: 0.5%, Ni: 25.0%, with the balance being Fe and inevitable impurities; all the weighed raw materials after batching are subjected to vacuum induction melting to obtain an alloy melt;

[0049] b. This step is the same as in Example 1.

[0050] Microscopic observation and analysis are carried out on the prepared gadolinium-rich iron-nickel-based alloy. The microstructure of the gadolinium-rich iron-nickel-based alloy mainly consists of austenite and high-melting-point second-phase (Ni,Cr,Fe) 5 Gd intermetallic compounds; in the gadolinium-rich iron-nickel-based alloy, the high-melting-point second-phase (Ni,Cr,Fe) 5 Gd is distributed along the austenite grain boundaries in the matrix, and the length dimension of the austenite grains is not greater than 150 μm. Through experimental tests, the test results show that the room-temperature tensile fracture strength of the gadolinium-rich iron-nickel-based alloy material rod prepared in this example is greater than 500.0 MPa, and the fracture elongation is greater than 40.0%. The mechanical and corrosion-resistant properties of the iron-nickel-based alloy material prepared in this example are superior to those of traditional boron steel or B 4 C / Al-based composites, and can be used as components such as pipe materials and plates for reactor spent fuel storage and other aspects. It is the best candidate material to replace traditional boron steel or B 4 C / Al-based composites and other series in the future, and can greatly reduce the raw material cost.

[0051] Example 5:

[0052] This example is basically the same as the previous examples, with the special feature being:

[0053] In this example, a preparation method of a special steel-based alloy material for nuclear shielding includes the following steps:

[0054] a. Using the vacuum induction melting process, when preparing the raw material mixture, the raw material components are proportioned according to the following mass percentages (%): C: 0.028%, Cr: 18.0%, Gd: 2.5%, Ni: 30.0%, Mo: 2.5%, with the balance being Fe and inevitable impurities; all the weighed raw materials after batching are subjected to vacuum induction melting to obtain an alloy melt;

[0055] b. This step is the same as that in Example 1.

[0056] The prepared gadolinium-rich iron-nickel-based alloy was microscopically observed and analyzed. The microstructure of the gadolinium-rich iron-nickel-based alloy mainly consists of austenite and high-melting-point second-phase (Ni, Cr, Fe) 5 Gd intermetallic compounds; in the gadolinium-rich iron-nickel-based alloy, the high-melting-point second-phase (Ni, Cr, Fe) 5 Gd is distributed along the austenite grain boundaries in the matrix, and the length dimension of the austenite grains is not greater than 150 μm. Through experimental tests, the test results show that the room-temperature tensile fracture strength of the gadolinium-rich iron-nickel-based alloy material rod prepared in this example is greater than 500.0 MPa, and the fracture elongation is greater than 40.0%. The mechanical and corrosion-resistant properties of the iron-nickel-based alloy material prepared in this example are superior to those of traditional boron steel or B 4 C / Al-based composites and can be used as components such as tubes and plates for reactor spent fuel storage, etc. It is the best candidate material to replace traditional boron steel or B 4 C / Al-based composites and other series, which can significantly reduce the raw material cost.

[0057] Example 6:

[0058] This example is basically the same as the previous examples, with the special feature being:

[0059] In this example, a preparation method of an iron-nickel-based alloy material for nuclear shielding includes the following steps:

[0060] a. Using the vacuum induction melting process, when formulating the raw materials, the raw material components are formulated according to the following mass percentages (%): C: 0.018%, Cr: 22.0%, Gd: 3.0%, Ni: 35.0%, Mo: 5.0%, and the balance is Fe and unavoidable impurities; all the weighed raw materials after formulation are subjected to vacuum induction melting to obtain an alloy melt;

[0061] b. This step is the same as that in Example 1.

[0062] The prepared gadolinium-rich iron-nickel-based alloy was microscopically observed and analyzed. The microstructure of the gadolinium-rich iron-nickel-based alloy mainly consists of austenite and high-melting-point second-phase (Ni, Cr, Fe) 5 Gd intermetallic compounds; in the gadolinium-rich iron-nickel-based alloy, the high-melting-point second-phase (Ni, Cr, Fe) 5Gd is distributed along the austenite grain boundaries in the matrix, and the length dimension of the austenite grains is not greater than 150 μm. Through experimental tests, the test results show that the room-temperature tensile fracture strength of the gadolinium-rich iron-nickel-based alloy material rod prepared in this example is greater than 550.0 MPa, and the fracture elongation is greater than 35.0%. The mechanical and corrosion resistance properties of the iron-nickel-based alloy material prepared in this example are superior to those of traditional boron steel or B 4 C / Al-based composites, and can be used as components such as pipe materials and plates for reactor spent fuel storage and other aspects. It is the best candidate material to replace traditional boron steel or B 4 C / Al-based composites and other series, which can greatly reduce the raw material cost.

[0063] Example Seven:

[0064] This example is basically the same as the previous examples, with the special feature being:

[0065] In this example, a preparation method of an iron-nickel-based alloy material for nuclear shielding includes the following steps:

[0066] a. Adopt the vacuum induction melting process. When preparing the raw material ingredients, the raw material components are prepared according to the following mass percentage (%): C: 0.013%, Cr: 25.0%, Gd: 1.5%, Ni: 38.0%, Mo: 3.5%, and the balance is Fe and unavoidable impurities; all the weighed raw materials after batching are subjected to vacuum induction melting to obtain an alloy melt;

[0067] b. This step is the same as that in Example One.

[0068] Microscopic observation and analysis are carried out on the prepared gadolinium-rich iron-nickel-based alloy. The gadolinium-rich iron-nickel-based alloy structure mainly consists of austenite and high-melting-point second-phase (Ni, Cr, Fe) 5 Gd intermetallic compounds; in the gadolinium-rich iron-nickel-based alloy, the high-melting-point second-phase (Ni, Cr, Fe) 5 Gd is distributed along the austenite grain boundaries in the matrix, and the length dimension of the austenite grains is not greater than 150 μm. Through experimental tests, the test results show that the room-temperature tensile fracture strength of the gadolinium-rich iron-nickel-based alloy material rod prepared in this example is greater than 500.0 MPa, and the fracture elongation is greater than 40.0%. The mechanical and corrosion resistance properties of the iron-nickel-based alloy material prepared in this example are superior to those of traditional boron steel or B 4 C / Al-based composites, and can be used as components such as pipe materials and plates for reactor spent fuel storage and other aspects. It is the best candidate material to replace traditional boron steel or B 4 C / Al-based composites and other series, which can greatly reduce the raw material cost.

[0069] In the above-described first to seventh embodiments of the present invention, a gadolinium-rich iron-nickel-based alloy material is prepared, which fully exploits the advantages of gadolinium (Gd) element having a large equivalent neutron absorption cross-section, good thermal stability, and thermal neutron radiation stability. Existing gadolinium-rich 304L and 316L alloys have certain corrosion resistance and mechanical properties. However, in iron-based austenitic stainless steel alloys such as gadolinium-rich 304Gd and gadolinium-rich 316Gd, since gadolinium does not dissolve in the matrix but forms a low-melting-point compound (Fe,Cr,Ni) 3 Gd, whose melting point is around 1060 °C, which makes it difficult to perform hot working on the material, affecting the hot working performance and mechanical properties of the material. In addition, due to the presence of low-melting-point Gd-rich precipitation phases, the material does not have excellent welding properties, so it is difficult to make large components that meet the nuclear shielding requirements. The gadolinium-rich Hastelloy C-4 (00Cr16Ni66Mo16Ti + 1.58Gd), Hastelloy C-22 (00Cr21Ni57Mo13W3 + 1.98Gd), Alloy 59 (00Cr23Ni59Mo16 + 1.82Gd), etc., developed by the Idaho National Laboratory in the United States in cooperation with Lehigh University. In these alloys, Gd forms a high-melting-point compound Ni 5 Gd, whose melting point is around 1260 °C, which is very beneficial to its hot working. However, these Ni-based alloys have a high Mo content and a high Ni content, making their cost high, which also limits their large-scale application. The gadolinium-rich iron-nickel-based alloy material prepared in the above-described first to seventh embodiments of the present invention can provide a new type of low-molybdenum, ultra-low-molybdenum or molybdenum-free gadolinium-rich iron-nickel-based alloy material by adjusting the raw material ratio of nickel and iron, reducing the usage of Ni and Mo, and appropriately increasing the iron content, which is more conducive to the formation of a composite phase structure, significantly reduces the raw material cost, and at the same time reduces the burning loss of high-cost metal raw materials, obtaining a better material performance-price ratio and being more suitable for industrial production applications. In addition, the gadolinium-rich iron-nickel-based alloy material of the present invention does not need to add alloying elements such as Ti and W, making the alloy composition simpler and easier to melt and cast.

[0070] For the gadolinium-rich iron-nickel-based alloy material, the patent document with the publication number CN110273085A discloses a gadolinium-rich nickel-based alloy material for storing spent reactor fuel. Its main components are composed according to the following mass percentages (%): C ≤ 0.03, N ≤ 0.02, S ≤ 0.01, P ≤ 0.03, Cr: 18.0 - 35.0, Gd: 0.5 - 5.0, Fe: 0 - 10.0, and the rest is nickel and inevitable impurities. The gadolinium-rich nickel-based alloy material for storing spent reactor fuel can synthesize uniformly dispersed micro-nano (Ni,Cr)5Gd particles by adding appropriate proportions of nickel, chromium, and gadolinium during the vacuum induction melting process of nickel-based austenitic alloy, and make the micro-nano (Ni,Cr)5Gd particles uniformly dispersed in the nickel-based alloy material. The lowest mass percentage content of nickel added is not less than 49%, and the Fe content is not higher than 10%. However, for the gadolinium-rich iron-nickel-based alloy material of the present invention, the mass percentage content of nickel added is not higher than 45%, and the Fe content is not less than 24%. It can be seen that compared with the gadolinium-rich nickel-based alloy material for storing spent reactor fuel disclosed in the patent document with the publication number CN110273085A, the gadolinium-rich iron-nickel-based alloy material of the present invention replaces part of the nickel with iron, significantly reducing the material cost. In addition, through a large number of experimental studies, it is known that in the FeCrNi alloy, by regulating the Ni / Fe ratio, the type of gadolinium-rich precipitation phase formed can be changed, that is, it is necessary to generate only high-melting-point (Ni,Cr,Fe) 5 Gd in the alloy, rather than generating low-melting-point (Fe,Cr,Ni) 3 Gd, (Ni,Cr,Fe) 5 Gd has higher thermal stability than (Fe,Cr,Ni) 3 Gd. During the vacuum induction melting process of the iron-nickel-based alloy, by adding appropriate proportions of gadolinium, chromium, and molybdenum and controlling the Ni / Fe ratio, a gadolinium-rich iron-nickel-based alloy material with excellent corrosion resistance and excellent hot working performance can be prepared. The gadolinium-rich iron-nickel-based alloy material of the present invention is mainly composed of an austenite matrix and (Ni,Cr,Fe) 5 Gd intermetallic compounds distributed along the austenite grain boundaries. The fracture elongation rate of the gadolinium-rich iron-nickel-based alloy material of the present invention is not less than 35.0%, endowing the gadolinium-rich iron-nickel-based alloy material with excellent hot working performance, and making it more suitable for application in the field of nuclear shielding material technology to exert cost advantages and specific properties.

[0071] In summary, for the gadolinium-rich iron-nickel-based alloy material for nuclear shielding in the above embodiments, its main components are composed according to the following mass percentages (%): C ≤ 0.03, Cr: 15.0 - 25.0, Gd: 0.5 - 5.0, Ni: 20.0 - 45.0, and it satisfies 0.40 ≤ mass ratio of Ni / Fe ≤ 1.8, with the remaining part being iron and inevitable impurities. An alloy melt is obtained through batching and vacuum induction melting processes; through casting, and then through processes such as hot forging, hot rolling, cold rolling, and annealing treatments, a rod, sheet, or tube of gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot working performance is finally prepared. The gadolinium-rich iron-nickel-based alloy material in the above embodiments of the present invention has the advantages of high strength, low cost, excellent corrosion resistance, and good processing and formability. Due to the substantial increase in the demand for nuclear power generation, developing neutron-absorbing structural materials for nuclear shielding used in the storage and transportation of spent nuclear fuel is an urgent requirement for the development of the nuclear industry. Since neutron-absorbing structural materials are irradiated by neutrons for a long time in the service environment, higher requirements are being placed on the corrosion resistance, mechanical properties, and neutron absorption ability of the materials. The present invention provides a material with further improved neutron absorption ability, which can store spent nuclear fuel on a larger scale, thereby improving the utilization efficiency of the material.

[0072] The above has described the embodiments of the present invention in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention of the present invention. Any changes, modifications, substitutions, combinations, or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent replacement methods. As long as it meets the invention purpose of the present invention and does not deviate from the technical principle and inventive concept of the special nickel-based alloy material for storing spent nuclear fuel in a reactor and its preparation method of the present invention, it belongs to the protection scope of the present invention.

Claims

1. A gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability, characterized in that, Its components are composed according to the following mass percentages: C ≤ 0.03, Cr: 15.0 - 25.0, Gd: 3.0 - 5.0, Ni: 35.0 - 45.0, and it satisfies 0.40 ≤ Ni / Fe mass ratio ≤ 1.8, with the remaining part being iron and inevitable impurities; the gadolinium-rich iron-nickel-based alloy structure mainly consists of austenite and high-melting-point second phases ((Ni, Cr, Fe)) 5 Gd intermetallic compounds; in the gadolinium-rich iron-nickel-based alloy, the high-melting-point second phases ((Ni, Cr, Fe)) 5 Gd is distributed along the austenite grain boundaries in the matrix.

2. The gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability according to claim 1, characterized in that, its composition further contains Mo element, and the composition of the gadolinium-rich iron-nickel-based alloy material for nuclear shielding is composed of the following mass percentages: C: 0.013 - 0.028, Cr: 15.0 - 25.0, Gd: 3.0 - 5.0, Ni: 35.0 - 45.0, Mo ≤ 8.0, and the rest is iron and unavoidable impurities.

3. The gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability according to claim 2, characterized in that, the composition is composed of the following mass percentages: C: 0.013 - 0.028, Cr: 15.0 - 25.0, Gd: 3.0 - 5.0, Ni: 38.0 - 45.0, Mo: 0 - 5.0, and the rest is iron and unavoidable impurities.

4. The gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability according to claim 1, characterized in that, the length dimension of the austenite grain is not greater than 150 μm.

5. The gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability according to claim 1, characterized in that, its room temperature tensile fracture strength is not less than 350 MPa, and the fracture elongation is not less than 35.0%.

6. The gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability according to claim 1, characterized in that, its room temperature tensile fracture strength is 350 - 600 MPa, and the fracture elongation is not less than 35.0%.

7. A preparation method of the gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability according to claim 1, characterized in that, it includes the following steps: a. Adopt the vacuum induction melting process. When preparing the raw material ingredients, the raw material composition is prepared according to the following mass percentages: C ≤ 0.03, Cr: 15.0 - 25.0, Gd: 0.5 - 5.0, Ni: 35.0 - 45.0, and 0.40 ≤ Ni / Fe mass ratio ≤ 1.8, and the rest is iron and unavoidable impurities; all the weighed raw materials after batching are subjected to vacuum induction melting, and the melting temperature is controlled to obtain an alloy melt; b. Cast the alloy melt prepared in step a into a mold, and the cast alloy ingot is successively subjected to hot forging, hot rolling, cold rolling and annealing heat treatment processes to finally obtain a rod or sheet or tube of the gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability.

8. The preparation method of the gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability according to claim 7, characterized in that: in step a, the raw material composition is prepared according to the following mass percentages: C: 0.013 - 0.028, Cr: 15.0 - 25.0, Gd: 3.0 - 5.0, Ni: 35.0 - 45.0, Mo ≤ 8.0, and the rest is iron and unavoidable impurities.

9. The preparation method of the gadolinium-rich iron-nickel-based alloy material for nuclear shielding with excellent hot workability according to claim 7, characterized in that: in the step a, in the step a, the raw material components are proportioned according to the following mass percentages: C: 0.013 to 0.028, Cr: 15.0 to 25.0, Gd: 3.0 to 5.0, Ni: 38.0 to 45.0, Mo: 0 - 5.0, and the rest is iron and inevitable impurities.

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