Iron-nickel-based high-temperature alloy with excellent thermal stability and long service life for fast reactor and preparation method of iron-nickel-based high-temperature alloy

Abstract

The invention discloses an iron-nickel-based high-temperature alloy with excellent thermal stability and long service life for a fast reactor and a preparation method of the iron-nickel-based high-temperature alloy, and belongs to the technical field of nuclear materials, the iron-nickel-based high-temperature alloy comprises the following chemical components in percentage by weight: 0.03-0.08% of C, 35.0-41.0% of Ni, 14.0-17.0% of Cr, 3.5-5.0% of Mo, 1.0-2.0% of Mn, 0.2-1.0% of Nb, 0-0.005% of B, 0-0.1% of Zr, 0-0.07% of Y and the balance of Fe. Nb and C satisfy 11 < = Nb / C < = 13, 0.25 * 10 <-5 > < = Nb * C < = 0.35 * 10 <-5 >, and Nb and Mo satisfy Nb + Mo > = 4.0 wt.%. The iron-nickel-based high-temperature alloy is good in alloy high-temperature structure and performance stability, sodium liquid corrosion resistance and neutron irradiation resistance, and can be used under the complex and harsh working condition of a sodium-cooled fast reactor.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear materials, and particularly relates to a long-life iron-nickel-based superalloy with excellent high-temperature microstructure and performance stability for advanced fourth-generation sodium-cooled fast reactors and a preparation method thereof, which is applicable to the key component materials facing the strong coupling environment of liquid sodium-thermal-mechanical-irradiation during ultra-long-term service in the fast reactor core. Background Art

[0002] Sodium-cooled fast reactors have extremely high safety, can significantly improve the utilization rate of uranium and greatly reduce nuclear waste, and are the main reactor types for China to develop the advanced nuclear energy system of the fourth-generation closed fuel cycle. Inside the huge and precise reactor, a large number of sodium-related moving parts (including nuts, guide tubes, positioning keys, etc.) serve in the high-temperature and highly chemically active liquid metal sodium coolant for a long time, posing harsh requirements on the microstructure, service performance, surface integrity, etc. of the materials.

[0003] At present, solution-strengthened iron-nickel-based superalloys have become the key materials for manufacturing sodium-related moving parts of fast reactors at home and abroad due to their excellent anti-neutron irradiation performance. The thermal processes that these components need to experience from preparation to service mainly include chromizing and nitriding surface protection treatment and ultra-long-term high-temperature service in the reactor core. The chromizing and nitriding treatment is to prepare a hard Cr2N coating on the surface of the components to prevent the components from self-welding and improve their surface wear resistance and sodium liquid corrosion resistance. The chromizing and nitriding process of domestic iron-nickel-based superalloys (patent CN114807832B) has a high temperature (up to 1150°C at most), a long time (up to 30h at most), and the cooling method is furnace cooling. The alloy will undergo grain coarsening and abnormal growth, and the grain boundary precipitates show continuous distribution, resulting in a serious decline in properties such as strength and impact toughness. In addition, the components after chromizing and nitriding treatment face high temperature (the short-term over-temperature can reach 750°C), alternating loads, sodium liquid corrosion and fast neutron irradiation during ultra-long-term service in the reactor. The complex microstructure evolutions such as grain boundary element segregation, brittle phase precipitation, and helium bubble formation in the alloy will also cause performance degradation of the material. Therefore, poor high-temperature grain stability, serious degradation inside and at the grain boundaries, and reduced comprehensive performance are the bottleneck problems faced by the localization of iron-nickel-based superalloy sodium-related moving parts.

[0004] Through systematic research, it has been found that for solution-strengthened iron-nickel-based superalloys, carbides and grain boundaries are the main microstructural features of the alloy and are also the key to affecting the above bottleneck problems. First of all, NbC, as a representative carbide, has excellent thermal stability. It can not only pin grain boundaries, refine and stabilize grain size, but also improve the high-temperature mechanical properties of the alloy. At the same time, it can inhibit the formation of Cr-rich brittle phases at grain boundaries, reduce the sensitivity to intergranular corrosion, and significantly improve the intergranular corrosion resistance (Wu Yang, Xie Ang, Chen Sheng Hu, et al. Liquid Pb-Bi eutectic corrosion behavior of NbC in Nb-containing austenitic stainless steel and its effect on oxide layer formation [J]. Acta Metallurgica Sinica, 61(2): 287-296.).Related studies have also shown that finely dispersed NbC can effectively capture defects such as voids generated by irradiation and reduce irradiation swelling behavior (Shin J H, Kong B S, Jeong C, et al. Swelling resistance of an austenitic stainless steel with uniformly distributed nanosized NbC precipitates under heavy ion irradiation [J]. Journal of Nuclear Materials, 2022, 564: 153678.); secondly, special grain boundaries, as low-energy grain boundaries with a low diffusion rate (Guan X J, Shi F, Ji H M, et al. A possibility to synchronously improve the high-temperature strength and ductility in face-centered cubic metals through grain boundary engineering [J]. Scripta Materialia, 2020, 187: 216-220.), have a low sensitivity to solute atom segregation and at the same time have a high resistance to the initiation of local corrosion. They can not only effectively improve the stability of the alloy's high-temperature microstructure and properties but also improve the resistance to intergranular stress corrosion (Lehockey E M, Brennenstuhl A M, Thompson I. On the relationship between grain boundary connectivity, coincidence site lattice boundaries, and intergranular stress corrosion cracking [J]. Corrosion Science, 2004, 46(10): 2383-2404. and Jones R, Randle V. Sensitisation behaviour of grain boundary engineered austenitic stainless steel [J]. Materials Science and Engineering A, 2010, 527(16-17): 4275-4280.).It can be seen that optimizing carbides and special grain boundaries has great development potential for improving the comprehensive properties of nuclear-grade iron-nickel-based superalloys, and the optimization effect is closely related to alloy composition design and preparation process. In view of this, how to synergistically regulate carbides and special grain boundaries through composition and process to obtain long-life sodium-exposed moving part materials with excellent high-temperature microstructure and performance stability, good sodium corrosion resistance and neutron irradiation resistance has become a key technical problem that urgently needs to be solved in the development and engineering application of sodium-cooled fast reactor technology in China.

[0005] In the existing publicly available related technologies and literatures, generally only single regulation of carbides or special grain boundaries in the alloy is concerned, and there is no relevant research and report on the synergistic regulation of the two. The precipitation of carbides will hinder the formation of special grain boundaries, while the formation of special grain boundaries will inhibit the precipitation of carbides. Solving the mutual competition relationship between the two through reasonable composition and process design is the key point of the technical solution of the present invention. Summary of the Invention

[0006] Aiming at the bottleneck problems in the field of the fourth-generation advanced nuclear energy, the purpose of the present invention is to provide a long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors and its preparation method. Through alloy composition design and microstructure regulation, a long-life iron-nickel-based superalloy material for sodium-exposed moving parts with excellent high-temperature microstructure and performance stability, good sodium corrosion resistance and neutron irradiation resistance is obtained, meeting the use requirements of the chromizing and nitriding process and the subsequent extremely harsh in-pile high-temperature long-term service environment.

[0007] In order to achieve the above purpose, the technical solution of the present invention is as follows:

[0008] A long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, by weight percentage, the chemical composition of the superalloy is: C 0.03% - 0.08%, Ni 35.0% - 41.0%, Cr 14.0% - 17.0%, Mo 3.5% - 5.0%, Mn 1.0% - 2.0%, Nb 0.2% - 1.0%, B 0% - 0.005%, Zr 0% - 0.1%, Y 0% - 0.07%, and the balance is Fe.

[0009] Further, for the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, the Nb content and C content satisfy: 11 ≤ Nb / C ≤ 13, 0.25×10 -5 ≤ Nb×C ≤ 0.35×10 -5 , and the Nb content and Mo content satisfy: Nb + Mo ≥ 4.0 wt.%.

[0010] The preparation method of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors described in the present invention includes the following steps:

[0011] (1) Preparation of raw materials: According to the chemical composition ratio of the alloy, high-quality industrial pure iron, electrolytic nickel (GB / T 6516 - 2010), metallic chromium (GB / T 3211 - 2008), metallic molybdenum (GB / T 17792 - 1999), metallic manganese (GB / T 2774 - 2006), metallic niobium (GB / T 14842 - 2007), metallic zirconium (GB / T 26314 - 2010), pyrolytic graphite (GB / T1426 - 1978) and other master alloys: nickel boron alloy (containing 15.634% B by weight percentage), nickel yttrium alloy (containing 19.98% Y by weight percentage) are used as raw materials;

[0012] (2) Double - vacuum smelting: The prepared alloy is charged and undergoes double - vacuum smelting of vacuum induction melting and vacuum consumable remelting to obtain an alloy ingot;

[0013] (3) Homogenization treatment: After cutting off the riser of the alloy ingot, it is heated in the furnace to 1210 °C - 1230 °C and held for 15 h - 30 h;

[0014] (4) Forging: The ingot after high - temperature homogenization is held at 1050 °C - 1170 °C for 2 h - 4 h and then forged to obtain a forged billet;

[0015] (5) Hot rolling: The forged billet is held at 1050 °C - 1170 °C for 2 h - 4 h and then hot - rolled to obtain hot - rolled sheets;

[0016] (6) Solution treatment: The hot - rolled sheets are placed in a non - vacuum muffle furnace, held at 1100 °C - 1150 °C for 30 min - 60 min and then air - cooled;

[0017] (7) Small - deformation deep cold rolling: After polishing the upper and lower surfaces of the sheets after solution treatment until they are shiny, deep cold rolling is carried out. Before rolling on a two - high cold rolling mill, the sheets are immersed in liquid nitrogen. The total deformation is controlled at 5% - 12%, and the number of rolling passes is controlled at 1 - 10 times to obtain deep - cold - rolled sheets;

[0018] (8) Two - stage heat treatment: The cold - rolled sheets are placed in a non - vacuum muffle furnace. First, they are held at 1100 °C - 1150 °C for 1 h - 10 h, and then cooled in the furnace to 900 °C - 1000 °C and held for 0.5 h - 4 h.

[0019] Further, for the preparation method of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, in step (2) double-vacuum smelting: the impurity elements in the ingot after vacuum smelting meet the following requirements by weight percentage: Al ≤ 0.050%, Ti ≤ 0.030%, Co ≤ 0.1%, Cu ≤ 0.030%, S ≤ 0.001%, P ≤ 0.005%, Si ≤ 0.030%, O ≤ 0.01%, N ≤ 0.01%, Pb ≤ 0.001%, Sb ≤ 0.01%, Bi ≤ 0.0001%, As ≤ 0.005%, Sn ≤ 0.005%.

[0020] Further, for the preparation method of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, in step (2) double-vacuum smelting: before vacuum smelting, the raw materials need to be systematically pretreated, including surface treatment and vacuum degassing.

[0021] Further, for the preparation method of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, in step (4) forging: the ingot after high-temperature homogenization is forged after being held at 1050°C to 1170°C for 2h to 4h, and the strain rate is 0.01s -1 ~1.0s -1 , the engineering strain is above 60%, and the final forging temperature is above 950°C. Reheating in the furnace is allowed before forging to the final specification, and it is held at 1050°C to 1170°C for 1h to 2h.

[0022] Further, for the preparation method of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, in step (5) hot rolling: the forged billet is hot-rolled after being held at 1050°C to 1170°C for 2h to 4h, and the strain rate is 2.0s -1 ~10s -1 , the engineering strain is above 70%, and the final rolling temperature is above 950°C to obtain hot-rolled sheets with a thickness of 6mm to 12mm. Reheating in the furnace is allowed before hot rolling to the final specification, and it is held at 1050°C to 1170°C for 1h to 2h.

[0023] Further, for the preparation method of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, in step (7) small-deformation deep cold rolling: before rolling on a two-high cold rolling mill, the sheet is immersed in liquid nitrogen for 1h to 2h, and after each 1 to 2 passes of rolling, the sheet is re-immersed in liquid nitrogen for 10min to 30min to finally obtain deep cold-rolled sheets with a thickness of 5.70mm to 11.40mm.

[0024] Further, for the preparation method of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, after the two-stage heat treatment in step (8), the non-metallic inclusions in the sheet meet the following requirements: for the fine series (m), A ≤ 0.5 grade, B ≤ 1.0 grade, D ≤ 2.0 grade, and the sum of the three categories ≤ 2.5 grades; for the coarse series (m), A ≤ 0.5 grade, B ≤ 1.0 grade, D ≤ 1.0 grade, and the sum of the three categories ≤ 1.5 grades; where A is sulfide type, B is alumina type, D is spherical oxide type, and the sum of the three categories is A + B + D.

[0025] Further, for the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors prepared by the above preparation method, the total proportion of ∑≤29 grain boundaries in the alloy is not less than 70%, and the ratio v between the size of the twin-related region (TRD) and the grain size is not less than 3.

[0026] Further, for the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors prepared by the above preparation method, after holding at 1140°C for 30 h, the average grain size of the alloy does not exceed 2 times that after the two-stage heat treatment, and it has excellent high-temperature grain stability.

[0027] Further, for the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors prepared by the above preparation method, its initial structure is austenite and NbC, NbC is evenly dispersed in a spherical / blocky shape, and the single-particle size of NbC < 2 μm; after cooling in the furnace at 1140°C for 30 h or aging at 600°C for 5000 h, the structure is still austenite and NbC, and it has excellent structure stability.

[0028] Further, for the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors prepared by the above preparation method, after cooling in the furnace at 1140°C for 30 h or aging at 600°C for 5000 h, the tensile properties of the alloy at 750°C meet the following requirements: the yield strength (Rp0.2) is not less than 120 MPa, the tensile strength (Rm) is not less than 280 MPa, and the elongation (A) is not less than 50%; the room-temperature impact toughness (KV2) is not less than 400 J / cm 2 and it has excellent performance stability.

[0029] Further, for the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors prepared by the above preparation method, after the two-stage heat treatment, the creep properties of the alloy at 750°C / 135 MPa meet the following requirements: the creep life is not less than 180 h, the elongation (A) is not less than 70%, and it still has excellent performance under the thermo-mechanical coupling effect of over-temperature service.

[0030] The design concept of the present invention is:

[0031] (1) Low-defect and pure smelting:

[0032] Guided by the low segregation technology, the master alloy ingot of Fe-Ni-based superalloy is prepared by the double-purification smelting process of vacuum induction melting and vacuum consumable remelting. Before smelting, the raw materials are subjected to surface treatment and vacuum degassing to minimize the content of gas elements and inclusions, improve the purity of the alloy, and effectively reduce the failure sources in the alloy.

[0033] (2) Fine composition design:

[0034] Based on the idea of fine composition design of the alloy, the beneficial effects of each element are fully exerted. The Ni content in the alloy is set at 35.0 wt.% - 41.0 wt.% to ensure that the alloy has good anti-irradiation swelling performance and high-temperature stability; the optimal solution strengthening effect of the alloy is achieved by the reasonable addition of Nb and Mo, and the Nb content and Mo content satisfy Nb + Mo ≥ 4.0 wt.%; microalloying with C, B, and Zr improves the grain boundary bonding force on the one hand and promotes the formation of NbC strengthening phase on the other hand; the content of Cr is strictly controlled to control the precipitation of Cr-rich brittle phases at grain boundaries to ensure plastic toughness and sodium liquid corrosion resistance.

[0035] Considering the interaction and synergistic effect of the key alloying elements Nb and C, the Nb / C and Nb×C values of the alloy are reasonably designed. When the Nb / C value is too high, Nb-rich brittle phases are likely to precipitate at grain boundaries and within grains. When the Nb / C value is too low, Cr-rich brittle phases are likely to precipitate at grain boundaries and within grains, both of which will damage the service performance of the alloy; when the Nb×C value is too high, the size and quantity of NbC precipitation phases increase, reducing the solution strengthening effect and promoting crack initiation. When the Nb×C value is too low, the quantity of NbC precipitation phases decreases, which is not sufficient to play the role of second-phase precipitation strengthening, and it is difficult to effectively hinder the grain growth during the chromizing and nitriding processes.

[0036] (3) Synergistic regulation of multi-scale carbides and low-energy grain boundaries:

[0037] First, an integrated thermo-mechanical treatment such as homogenization, hot deformation, deep cold rolling, and heat treatment is adopted to introduce nano / micron multi-scale NbC precipitation phases into the single-phase austenitic alloy structure. On the one hand, the alloy obtains high strength and creep life through nano-NbC, and at the same time has good plasticity and toughness. On the other hand, sub-micron NbC provides Zener pinning force during the chromizing nitriding process, inhibits grain boundary migration and grain growth, and improves the high-temperature grain stability. This process can effectively avoid the existence of a large number of coarse and massive NbC (more than 3 μm) in the structure, which is not conducive to the liquid metal compatibility of the alloy. The liquid metal will invade along the interface between the matrix and the large-size NbC, promoting the local dissolution and corrosion of the austenitic matrix at the interface. In the integrated thermo-mechanical treatment of the present invention, after the coarse NbC is basically dissolved, the precipitation process of secondary NbC is cleverly designed in the early hot working and the subsequent two-stage heat treatment furnace cooling process, so that NbC precipitates in a dispersed and fine form, realizing the multi-scale distribution of NbC and minimizing the competitive influence between the precipitation of NbC and the formation of special grain boundaries to the greatest extent. In addition, the Nb element dissolved in the alloy matrix can inhibit the precipitation of Cr-rich brittle phases at grain boundaries after chromizing nitriding or high-temperature aging, and at the same time can play the role of the "third component effect", reducing the critical concentration required for the formation of oxides, promoting the formation of continuous oxides, and thus improving the grain boundary bonding force and liquid metal corrosion resistance of the alloy.

[0038] Secondly, through the regulation method of small deformation deep cold rolling + high-temperature long-time heat treatment, the proportion of low-energy special grain boundaries (∑≤29 grain boundaries) in the alloy is increased. Compared with room temperature rolling, deep cold rolling can significantly increase the dislocation density in the deformed matrix, reduce the dislocation mobility and the average free path of dislocation entanglement. Under the subsequent thermal activation of high temperature and long time, it can effectively promote grain boundary migration, enabling a sufficient proliferation reaction of low-energy special grain boundaries (low ∑3 n (n = 1, 2 or 3) grain boundaries) to occur inside the alloy, realizing the optimization of grain boundary character distribution, reducing the Gibbs free energy of the alloy, and improving the high-temperature grain stability. As described above, when a large number of coarse and massive NbC are distributed in the matrix, it will act as a nucleation site to promote the occurrence of recrystallization, which is not conducive to the formation of low-energy special grain boundaries. After eliminating the coarse and massive NbC in the present invention, it is beneficial to the proliferation reaction of low-energy special grain boundaries, becoming one of the key designs for their synergistic regulation. The proportion of high- and low-energy special grain boundaries and the v value obtained after the optimization of grain boundary character distribution can further improve the sodium liquid corrosion resistance and neutron irradiation resistance of the alloy. In summary, through the synergistic regulation of multi-scale carbides and low-energy grain boundaries, while ensuring excellent high-temperature tissue performance stability, the comprehensive service performance of the alloy can be effectively improved.

[0039] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0040] 1. In the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors disclosed by the present invention, the contents of gas elements, impurity elements and non-metallic inclusions are low, the multi-scale NbC precipitation phases are uniformly dispersed, the proportion of low-energy special grain boundaries is high, and the connectivity of the random large-angle grain boundary network is effectively blocked. It has excellent high-temperature microstructure and performance stability, good sodium corrosion resistance and neutron irradiation resistance, and can be used under the complex and harsh working conditions of sodium-cooled fast reactors. At the same time, it provides more theoretical basis and practical guidance for the collaborative regulation of multi-scale carbides and low-energy grain boundaries in other materials.

[0041] 2. In the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors of the present invention, the total proportion of ∑≤29 grain boundaries in the alloy is not less than 70%, and the ratio v between the TRD size and the grain size is not less than 3.

[0042] 3. After the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors of the present invention is held at 1140°C for 30 h, the average grain size of the alloy does not exceed 2 times that after two-stage heat treatment, and it has excellent high-temperature grain stability.

[0043] 4. The initial microstructure of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors of the present invention is austenite and NbC. The NbC is uniformly dispersed in a spherical / blocky shape, and the single-particle size of NbC is <2 μm. After being cooled in the furnace at 1140°C for 30 h or aged at 600°C for 5000 h, the microstructure is still austenite and NbC, and it has excellent microstructure stability.

[0044] 5. After the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors of the present invention is cooled in the furnace at 1140°C for 30 h or aged at 600°C for 5000 h, the tensile properties at 750°C of the alloy meet the following requirements: the yield strength (Rp0.2) is not less than 120 MPa, the tensile strength (Rm) is not less than 280 MPa, and the elongation (A) is not less than 50%; the room-temperature impact toughness (KV2) is not less than 400 J / cm 2 , and it has excellent performance stability.

[0045] 6. The creep properties at 750°C / 135 MPa of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors of the present invention meet the following requirements: the creep life is not less than 180 h, the elongation (A) is not less than 70%, and it still has excellent performance under the thermo-mechanical coupling effect of over-temperature service.

[0046] 7. The preparation method of the long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors of the present invention is simple and the cost is low. It can be prepared and processed into sodium-related moving parts of different specifications to meet the application requirements of sodium-cooled fast reactors. Description of the Drawings

[0047] Figure 1Morphology map of multi-scale carbides of a long-life iron-nickel-based superalloy with excellent thermal stability prepared in Example 2.

[0048] Figure 2 Low-energy special grain boundary distribution map of a long-life iron-nickel-based superalloy with excellent thermal stability prepared in Example 2.

[0049] Figure 3 Statistical result map of special grain boundaries of a long-life iron-nickel-based superalloy with excellent thermal stability prepared in Example 2; in the figure, the abscissa Sigma-Value represents the type of special grain boundary, and the ordinate Fraction represents the proportion of special grain boundaries (%).

[0050] Figure 4 Morphology map of coarse NbC carbides in the iron-nickel-based superalloy prepared in Example 3.

[0051] Figure 5 Orientation imaging map (IPF) and grain boundary morphology map of the iron-nickel-based superalloys prepared in Examples 1-2, 6 and Comparative Examples 1-3 after furnace cooling at 1140 °C for 30 h.

[0052] Figure 6 Microstructure morphology map of the iron-nickel-based superalloys prepared in Example 1 and Comparative Examples 1-3 after aging at 600 °C for 5000 h. Detailed implementation manners

[0053] To further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following combines the drawings and preferred embodiments to detail the specific implementation manners, structures, features and their effects of the application according to the present invention. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0054] In the specific implementation process, the present invention ensures the excellent thermal stability of the alloy based on the introduction of multi-scale NbC precipitation phases and the regulation of low-energy special grain boundaries, and prepares alloy sheets by the method of vacuum induction melting → vacuum consumable remelting → homogenization treatment → forging → hot rolling → solution treatment → small deformation deep cold rolling → two-stage heat treatment.

[0055] A long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, the alloy composition meets the following requirements in weight percentage: C 0.03% - 0.08%, Ni 35.0% - 41.0%, Cr 14.0% - 17.0%, Mo 3.5% - 5.0%, Mn 1.0% - 2.0%, Nb 0.2% - 1.0%, B 0% - 0.005%, Zr 0% - 0.1%, Y 0% - 0.07%, and the balance is Fe, where the Nb content and C content meet: 11 ≤ Nb / C ≤ 13, 0.25×10 -5 ≤ Nb×C ≤ 0.35×10 -5 , and the Nb content and Mo content meet: Nb + Mo ≥ 4.0 wt.%.

[0056] A preparation method of a long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors, comprising the following steps:

[0057] (1) Alloy preparation: According to the chemical composition ratio of the alloy, high-quality industrial pure iron, electrolytic nickel (GB / T 6516-2010), metallic chromium (GB / T 3211-2008), metallic molybdenum (GB / T 17792-1999), metallic manganese (GB / T 2774-2006), metallic niobium (GB / T 14842-2007), metallic zirconium (GB / T 26314-2010), pyrolytic graphite (GB / T1426-1978) and other master alloys: nickel-boron alloy (containing B 15.634% by weight), nickel-yttrium alloy (containing Y 19.98% by weight) are used as raw materials.

[0058] (2) Double vacuum melting: Before melting, the raw materials are systematically pretreated, including surface treatment and vacuum degassing. First, high-quality industrial pure iron, electrolytic nickel, metallic chromium, metallic molybdenum, metallic niobium and pyrolytic graphite are loaded into the crucible, and vacuum induction melting is carried out using a magnesia crucible containing a small amount of calcium oxide. Refining treatment is carried out at 1435°C - 1465°C for 15 min - 20 min. After the refining is completed, argon is filled into the vacuum induction melting furnace, and then metallic manganese is added, and stirring is continued for 10 min - 15 min. Finally, metallic zirconium, nickel-boron alloy and nickel-yttrium alloy are added together, and stirring is continued for 10 min - 15 min, and casting is carried out at 1365°C - 1415°C to obtain an ingot. The ingot is subjected to vacuum consumable remelting to obtain the final required ingot;

[0059] The impurity elements in the ingot meet the following requirements by weight percentage: Al ≤ 0.050%, Ti ≤ 0.030%, Co ≤ 0.1%, Cu ≤ 0.030%, S ≤ 0.001%, P ≤ 0.005%, Si ≤ 0.030%, O ≤ 0.01%, N ≤ 0.01%, Pb ≤ 0.001%, Sb ≤ 0.01%, Bi ≤ 0.0001%, As ≤ 0.005%, Sn ≤ 0.005%.

[0060] (3) Homogenization treatment: After cutting off the riser from the smelted ingot, a mixed slurry prepared from white fused alumina powder and silica sol is evenly coated on the surface of the ingot to reduce the oxidation effect during the subsequent high-temperature homogenization treatment. The coating is applied 6 - 8 times. After the ceramic slurry is completely dried, the ingot is loaded into a heat treatment furnace. The ingot is heated to 1000°C at a heating rate not exceeding 10°C / min, and then continued to be heated to 1210°C - 1230°C at a heating rate not exceeding 5°C / min. It is kept warm in the heat treatment furnace for 15h - 30h, and finally air-cooled to room temperature.

[0061] (4) Forging: The ingot after high-temperature homogenization is kept at 1050°C - 1170°C for 2h - 4h and then forged. The strain rate is 0.01s -1 ~1.0s -1 , the engineering strain is above 60%, and the final forging temperature is above 950°C to obtain a forged blank; it is allowed to be reheated in the furnace before forging to the final specification, and kept at 1050°C - 1170°C for 1h - 2h; preferably, the holding temperature of the above ingot is 1120°C - 1150°C.

[0062] (5) Hot rolling: The forged blank is kept at 1050°C - 1170°C for 2h - 4h and then hot-rolled. The strain rate is 2.0s -1 ~10s -1 , the engineering strain is above 70%, and the final rolling temperature is above 950°C to obtain a hot-rolled sheet with a thickness of 6mm - 12mm; it is allowed to be reheated in the furnace before hot-rolling to the final specification, and kept at 1050°C - 1170°C for 1h - 2h. Preferably, the holding temperature of the above ingot is 1120°C - 1150°C;

[0063] (6) Solution treatment: The hot-rolled sheet is placed in a non-vacuum muffle furnace, kept at 1100°C - 1150°C for 30min - 60min and then air-cooled;

[0064] (7) Small-deformation deep cold rolling: After polishing the upper and lower surfaces of the solution-treated sheet to be bright, deep cold rolling is carried out. Before rolling on a two-high cold rolling mill, the sheet is immersed in liquid nitrogen for 1 h to 2 h to uniformly cool it to the liquid nitrogen temperature. Before rolling, large-sized sheets are pre-rolled to reduce the temperature of the rolls. Subsequently, the rolling deformation of the specimen is started, and the total deformation is controlled within 5% to 12%, and the number of rolling passes is controlled within 1 to 10 times. After every 1 to 2 rolling passes, the sheet is re-immersed in liquid nitrogen for 10 min to 30 min. Finally, a deep cold-rolled sheet with a thickness of 5.70 mm to 11.40 mm is obtained;

[0065] (8) Two-stage heat treatment: The cold-rolled sheet is placed in a non-vacuum muffle furnace. First, it is held at 1100 °C to 1150 °C for 1 h to 10 h, and then furnace-cooled to 900 °C to 1000 °C and held for 0.5 h to 4 h; Preferably, the holding time for the first-stage heat treatment is 1 h to 5 h, the holding temperature for the second-stage heat treatment is 950 °C to 1000 °C, and the holding time is 0.5 h to 2 h.

[0066] In the examples and comparative examples of the present invention, the equipment used for observing SEM and EBSD microstructures is a TESCAN MAIA3 field emission scanning electron microscope.

[0067] In the examples and comparative examples of the present invention, Channel 5 analysis software is used to process EBSD data, measure the average grain size, the total proportion of Σ≤29 grain boundaries, and the ratio v of the TRD size to the grain size, where TRD is the size of the twin-related region surrounded by large-angle grain boundaries. The calculation method for the high-temperature grain stability evaluation criterion is: the grain growth degree δ D = D t / D0, where D t is the grain size after chromizing and nitriding, and D0 is the initial grain size.

[0068] In the examples and comparative examples of the present invention, the standard for measuring the room-temperature impact toughness is GB / T 229-2020 "Metallic materials - Charpy pendulum impact test method".

[0069] In the examples and comparative examples of the present invention, the standards for measuring the tensile strength, yield strength, elongation, and reduction of area are GB / T 228.2-2015 "Metallic materials - Tensile testing - Part 2: High-temperature test method".

[0070] In the examples and comparative examples of the present invention, the standard for measuring the high-temperature creep rupture performance is GB / T2039–2012 "Metallic materials - Uniaxial tensile creep test method".

[0071] The present invention will be described in detail below with reference to the accompanying drawings and examples.

[0072] Example 1

[0073] A long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors. By weight percentage, the chemical composition of the iron-nickel-based superalloy is: C 0.05%, Ni 38%, Cr 15.5%, Mo 3.8%, Nb 0.55%, Mn 1.5%, B 0.0015%, Zr 0.03%, Y 0.03%, and the balance is Fe.

[0074] The preparation method of the above-mentioned iron-nickel-based superalloy includes the following steps:

[0075] (1) Raw material preparation: Prepare raw materials according to the above weight percentage ratio;

[0076] (2) Double-vacuum smelting: The prepared alloy is subjected to double-vacuum smelting of vacuum induction melting and vacuum consumable remelting according to a reasonable charging sequence to obtain the required alloy ingot;

[0077] (3) Homogenization treatment: After cutting off the riser of the smelted ingot, it is heated to 1220 °C in the furnace and held for 20 h;

[0078] (4) Forging: The ingot after high-temperature homogenization is held at 1150 °C for 2 h and then forged, with a strain rate of 0.08 s -1 , and the engineering strain is 60% to obtain a forged blank;

[0079] (5) Hot rolling: The forged blank is held at 1150 °C for 2 h and then hot-rolled, with a strain rate of 10 s -1 , and the engineering strain is 70% to obtain a hot-rolled sheet with a thickness of 12 mm;

[0080] (6) Solution treatment: The hot-rolled sheet is placed in a non-vacuum muffle furnace, held at 1120 °C for 30 min, and then air-cooled.

[0081] Example 2

[0082] A long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors. By weight percentage, the chemical composition of the iron-nickel-based superalloy is: C 0.05%, Ni 38%, Cr 15.5%, Mo 3.8%, Nb 0.55%, Mn 1.5%, B 0.0015%, Zr 0.03%, Y 0.03%, and the balance is Fe.

[0083] The preparation method of the above-mentioned iron-nickel-based superalloy includes the following steps:

[0084] (1) Raw material preparation: Prepare raw materials according to the above weight percentage ratio;

[0085] (2) Double-vacuum smelting: The prepared alloy is subjected to double-vacuum smelting of vacuum induction melting and vacuum consumable remelting according to a reasonable charging sequence to obtain the required alloy ingot;

[0086] (3) Homogenization treatment: After cutting off the riser of the ingot obtained by smelting, it is heated to 1220 °C in the furnace and held for 20 h;

[0087] (4) Forging: The ingot after high-temperature homogenization is held at 1150 °C for 2 h and then forged, with a strain rate of 0.08 s -1 , and the engineering strain is 60% to obtain a forging blank;

[0088] (5) Hot rolling: The forging blank is held at 1150 °C for 2 h and then hot-rolled, with a strain rate of 10 s -1 , and the engineering strain is 70% to obtain a hot-rolled sheet with a thickness of 12 mm;

[0089] (6) Solution treatment: The hot-rolled sheet is placed in a non-vacuum muffle furnace, held at 1120 °C for 30 min, and then air-cooled;

[0090] (7) Small-deformation deep cold rolling: After polishing the upper and lower surfaces of the sheet after solution treatment until they are shiny, deep cold rolling is carried out. Before rolling on a two-high cold rolling mill, the sheet is immersed in liquid nitrogen for 1 h, the total deformation is 7%, the number of rolling passes is controlled at 7 times, and every 2 rolling passes in the middle, the sheet is immersed in liquid nitrogen for 10 min. Finally, a deep cold-rolled sheet with a thickness of 11.16 mm is obtained;

[0091] (8) Two-stage heat treatment: The cold-rolled sheet is placed in a non-vacuum muffle furnace, first held at 1140 °C for 1 h, and then furnace-cooled to 950 °C and held for 2 h.

[0092] The microstructure of the long-life iron-nickel-based superalloy with excellent thermal stability prepared in Example 2 is shown in Figure 1 and Figure 2 , and it can be seen from Figure 1 that the grains show a homogeneous distribution, the structure is a single-phase austenite structure, and nano / sub-micron NbC carbides are dispersed in the matrix. It can be seen from Figure 2 and Figure 3 that there are high-density special grain boundaries in the structure, the total proportion of ∑≤29 grain boundaries is 75.6%, and the v value is 3.95, effectively blocking the connectivity of the random large-angle grain boundary network.

[0093] Example 3

[0094] A long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors. By weight percentage, the chemical composition of the iron-nickel-based superalloy is: C 0.05%, Ni 38%, Cr 15.5%, Mo 3.8%, Nb 0.55%, Mn 1.5%, B 0.0015%, Zr 0.03%, Y 0.03%, and the balance is Fe.

[0095] The preparation method of the above iron-nickel-based superalloy includes the following steps:

[0096] (1) Raw material preparation: Prepare raw materials according to the above weight percentage ratio;

[0097] (2) Double vacuum melting: The prepared alloy is subjected to double vacuum melting of vacuum induction melting and vacuum consumable remelting according to a reasonable charging sequence to obtain the required alloy ingot;

[0098] (3) Forging: The ingot is forged after holding at 1150°C for 2 h, and the strain rate is 0.08 s -1 , and the engineering strain is 60% to obtain a forged blank;

[0099] (4) Hot rolling: The forged blank is hot-rolled after holding at 1150°C for 2 h, and the strain rate is 10 s -1 , and the engineering strain is 70% to obtain a hot-rolled sheet with a thickness of 12 mm;

[0100] (5) Solution treatment: The hot-rolled sheet is placed in a non-vacuum muffle furnace, held at 1120°C for 30 min, and then air-cooled;

[0101] (6) Small deformation deep cold rolling: The surfaces of the sheet after solution treatment are polished until shiny and then subjected to deep cold rolling. Before rolling on a two-high cold rolling mill, the sheet is immersed in liquid nitrogen for 1 h, the total deformation is 7%, the number of rolling passes is controlled at 7 times, and every 2 rolling passes in the middle, the sheet is immersed in liquid nitrogen for 10 min. Finally, a deep cold-rolled sheet with a thickness of 11.16 mm is obtained;

[0102] (7) Two-stage heat treatment: The cold-rolled sheet is placed in a non-vacuum muffle furnace, first held at 1140°C for 1 h, and then furnace-cooled to 950°C and held for 2 h.

[0103] Compared with Example 2, in the preparation process of Example 3, there is no homogenization treatment step. Through microscopic structure observation confirmation ( Figure 4 ), a large number of coarse primary NbC carbides are contained in the as-cast structure of the alloy and are not dissolved in the matrix, resulting in difficulty in precipitating nano / sub-micron NbC carbides in the subsequent process. The coarse NbC carbides will also hinder grain boundary migration, be unfavorable for optimizing the grain boundary character distribution, and at the same time will damage the mechanical properties and sodium liquid corrosion resistance of the alloy.

[0104] Example 4

[0105] A long - life iron - nickel - based superalloy with excellent thermal stability for fast reactors. By weight percentage, the chemical composition of the iron - nickel - based superalloy is: C 0.05%, Ni 38%, Cr 15.5%, Mo 3.8%, Nb 0.55%, Mn 1.5%, B 0.0015%, Zr 0.03%, Y 0.03%, and the balance is Fe.

[0106] The preparation method of the above - mentioned iron - nickel - based superalloy includes the following steps:

[0107] (1) Raw material preparation: Prepare raw materials according to the above weight percentage ratio;

[0108] (2) Double - vacuum smelting: Put the prepared alloy into the furnace according to a reasonable charging sequence, and carry out double - vacuum smelting of vacuum induction melting and vacuum consumable remelting to obtain the required alloy ingot;

[0109] (3) Homogenization treatment: After cutting off the riser of the ingot obtained by smelting, heat it in the furnace to 1220 °C and hold for 20 h;

[0110] (4) Forging: Forge the ingot after high - temperature homogenization at 1150 °C for 2 h, with a strain rate of 0.08 s -1 , and the engineering strain is 60% to obtain a forging blank;

[0111] (5) Hot rolling: Hot - roll the forging blank at 1150 °C for 2 h, with a strain rate of 10 s -1 , and the engineering strain is 70% to obtain a hot - rolled sheet with a thickness of 12 mm;

[0112] (6) Two - stage heat treatment: Place the cold - rolled sheet in a non - vacuum muffle furnace, first hold it at 1140 °C for 1 h, and then cool it in the furnace to 950 °C and hold for 2 h.

[0113] Compared with Example 2, in the preparation process of Example 4, there are no solution treatment and small - deformation deep - cold rolling steps. There is a lack of strain energy introduced by small - deformation deep - cold rolling in the alloy, and it is impossible to obtain the driving force for recrystallization nucleation, so the proportion of special grain boundaries is difficult to effectively increase. In addition, due to the lack of structures such as dislocations introduced by deep - cold rolling, there are also a lack of corresponding nucleation sites for the precipitation of nano - NbC. Therefore, even if two - stage heat treatment is carried out, the effect of coordinated regulation of multi - scale carbides and low - energy grain boundaries cannot be achieved.

[0114] Example 5

[0115] A long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors. By weight percentage, the chemical composition of the iron-nickel-based superalloy is: C 0.05%, Ni 38%, Cr 15.5%, Mo 3.8%, Nb 0.55%, Mn 1.5%, B 0.0015%, Zr 0.03%, Y 0.03%, and the balance is Fe.

[0116] The preparation method of the above iron-nickel-based superalloy includes the following steps:

[0117] (1) Raw material preparation: Prepare raw materials according to the above weight percentage ratio;

[0118] (2) Double vacuum smelting: Put the prepared alloy into the furnace according to a reasonable charging sequence, and carry out double vacuum smelting of vacuum induction melting and vacuum consumable remelting to obtain the required alloy ingot;

[0119] (3) Homogenization treatment: After cutting off the riser of the ingot obtained by smelting, heat it up to 1220 °C in the furnace and hold for 20 h;

[0120] (4) Forging: Forge the ingot after high-temperature homogenization at 1150 °C for 2 h, with a strain rate of 0.08 s -1 , and the engineering strain is 60% to obtain a forging billet;

[0121] (5) Hot rolling: Hot roll the forging billet at 1150 °C for 2 h, with a strain rate of 10 s -1 , and the engineering strain is 70% to obtain a hot-rolled sheet with a thickness of 12 mm;

[0122] (6) Solution treatment: Place the hot-rolled sheet in a non-vacuum muffle furnace, hold it at 1120 °C for 30 min, and then air-cool it;

[0123] (7) Small-deformation deep cold rolling: Polish the upper and lower surfaces of the sheet after solution treatment until they are shiny, and then carry out deep cold rolling. Immerse the sheet in liquid nitrogen for 1 h before rolling on a two-high cold rolling mill. The total deformation is 7%, and the number of rolling passes is controlled within 7 times. Immerse the sheet in liquid nitrogen for 10 min every 2 rolling passes. Finally, obtain a deep cold-rolled sheet with a thickness of 11.16 mm;

[0124] (8) Two-stage heat treatment: Place the cold-rolled sheet in a non-vacuum muffle furnace. First, hold it at 1140 °C for 1 h, air-cool it to room temperature, and then hold it at 950 °C for 2 h and air-cool it to room temperature.

[0125] Compared with Example 2, in the two-stage heat treatment of Example 5 in step (8), the cooling method of the first-stage heat treatment is air cooling, and then it is reheated and held at 950 °C for 2 h. Compared with the furnace cooling method of the first-stage heat treatment, the driving force for atomic diffusion is greatly reduced, which is not conducive to the precipitation of nano-NbC. Therefore, furnace cooling must be used as a transition between the two-stage heat treatments.

[0126] Example 6

[0127] A long-life iron-nickel-based superalloy with excellent thermal stability for fast reactors. By weight percentage, the chemical composition of the iron-nickel-based superalloy is: C 0.05%, Ni 38%, Cr 15.5%, Mo 3.8%, Nb 0.55%, Mn 1.5%, B 0.0015%, Zr 0.03%, Y 0.03%, and the balance is Fe.

[0128] The preparation method of the above-mentioned iron-nickel-based superalloy includes the following steps:

[0129] (1) Raw material preparation: Prepare the raw materials according to the above weight percentage ratio;

[0130] (2) Double-vacuum smelting: The prepared alloy is subjected to double-vacuum smelting of vacuum induction melting and vacuum consumable remelting according to a reasonable charging sequence to obtain the required alloy ingot;

[0131] (3) Homogenization treatment: After cutting off the riser of the ingot obtained by smelting, it is heated to 1220 °C in the furnace and held for 20 h;

[0132] (4) Forging: The ingot after high-temperature homogenization is held at 1150 °C for 2 h and then forged. The strain rate is 0.08 s -1 , and the engineering strain is 60% to obtain a forging blank;

[0133] (5) Hot rolling: The forging blank is held at 1150 °C for 2 h and then hot-rolled. The strain rate is 10 s -1 , and the engineering strain is 70% to obtain a hot-rolled sheet with a thickness of 12 mm;

[0134] (6) Solution treatment: The hot-rolled sheet is placed in a non-vacuum muffle furnace, held at 1120 °C for 30 min, and then air-cooled;

[0135] (7) Small-deformation deep cold rolling: After the surfaces of the sheet after solution treatment are polished bright, deep cold rolling is carried out. Before rolling on a two-high cold rolling mill, the sheet is immersed in liquid nitrogen for 1 h. The total deformation is 3%, and the number of rolling passes is controlled at 2 times. Finally, a deep cold-rolled sheet with a thickness of 11.64 mm is obtained;

[0136] (8) Two-stage heat treatment: The cold-rolled sheet is placed in a non-vacuum muffle furnace, first held at 1140 °C for 1 h, and then furnace-cooled to 950 °C and held for 2 h.

[0137] Compared with Example 2, in the small-deformation deep cold rolling in step (7) of Example 6, the total deformation amount is less than the critical deformation amount.

[0138] Comparative Example 1

[0139] A nickel-based superalloy. By weight percentage, the chemical composition of the nickel-based superalloy is: C 0.05%, Ni 37%, Cr 15.6%, Mo 3.6%, Mn 1.6%, B 0.0015%, Zr 0.03%, Y 0.03%, and the balance is Fe.

[0140] The preparation method of the above nickel-based superalloy includes the following steps:

[0141] (1) Raw material preparation: Prepare raw materials according to the above weight percentage ratio;

[0142] (2) Double vacuum smelting: The prepared alloy is subjected to double vacuum smelting of vacuum induction melting and vacuum consumable remelting according to a reasonable charging sequence to obtain the required alloy ingot;

[0143] (3) Homogenization treatment: After cutting off the riser of the ingot obtained by smelting, it is heated to 1220 °C in the furnace and held for 20 h;

[0144] (4) Forging: The ingot after high-temperature homogenization is held at 1150 °C for 2 h and then forged, with a strain rate of 0.08 s -1 , and the engineering strain is 60% to obtain a forged blank;

[0145] (5) Hot rolling: The forged blank is hot rolled after being held at 1150 °C for 2 h, with a strain rate of 10 s -1 , and the engineering strain is 70% to obtain a hot-rolled sheet with a thickness of 12 mm;

[0146] (6) Solution treatment: The hot-rolled sheet is placed in a non-vacuum muffle furnace, held at 1120 °C for 30 min, and then air-cooled.

[0147] Comparative Example 2

[0148] A nickel-based superalloy. By weight percentage, the chemical composition of the nickel-based superalloy is: C 0.05%, Ni 37%, Cr 15.5%, Mo 3.8%, Nb 0.25%, Mn 1.6%, B 0.0015%, Zr 0.03%, Y 0.03%, and the balance is Fe.

[0149] The preparation method of the above nickel-based superalloy includes the following steps:

[0150] (1) Raw material preparation: Prepare raw materials according to the above weight percentage ratio;

[0151] (2) Double-vacuum smelting: The prepared alloy is subjected to double-vacuum smelting of vacuum induction melting and vacuum consumable remelting according to a reasonable charging sequence to obtain the required alloy ingot;

[0152] (3) Homogenization treatment: After cutting off the riser of the smelted ingot, it is heated to 1220 °C in the furnace and held for 20 h;

[0153] (4) Forging: The ingot after high-temperature homogenization is held at 1150 °C for 2 h and then forged, with a strain rate of 0.08 s -1 , and the engineering strain is 60% to obtain a forged blank;

[0154] (5) Hot rolling: The forged blank is hot-rolled after being held at 1150 °C for 2 h, with a strain rate of 10 s -1 , and the engineering strain is 70% to obtain a hot-rolled sheet with a thickness of 12 mm;

[0155] (6) Solution treatment: The hot-rolled sheet is placed in a non-vacuum muffle furnace, held at 1120 °C for 30 min and then air-cooled.

[0156] Comparative Example 3

[0157] A Fe-Ni-based superalloy, by weight percentage, the chemical composition of the Fe-Ni-based superalloy is: C 0.05%, Ni 37%, Cr 15.5%, Mo 3.7%, Nb 1.0%, B 0.0015%, Zr 0.03%, Y 0.03%, and the balance is Fe.

[0158] The preparation method of the above Fe-Ni-based superalloy includes the following steps:

[0159] (1) Raw material preparation: Prepare raw materials according to the above weight percentage ratio;

[0160] (2) Double-vacuum smelting: The prepared alloy is subjected to double-vacuum smelting of vacuum induction melting and vacuum consumable remelting according to a reasonable charging sequence to obtain the required alloy ingot;

[0161] (3) Homogenization treatment: After cutting off the riser of the smelted ingot, it is heated to 1220 °C in the furnace and held for 20 h;

[0162] (4) Forging: The ingot after high-temperature homogenization is held at 1150 °C for 2 h and then forged, with a strain rate of 0.08 s -1 , and the engineering strain is 60% to obtain a forged blank;

[0163] (5) Hot rolling: The forged blank is hot-rolled after being held at 1150 °C for 2 h, with a strain rate of 10 s -1, the engineering strain should be 70%, and a hot-rolled sheet with a thickness of 12 mm is obtained;

[0164] (6) Solution treatment: Place the hot-rolled sheet in a non-vacuum muffle furnace, hold it at 1120 °C for 30 min, and then air-cool.

[0165] Comparative Example 4

[0166] According to the alloy chemical compositions of the 12 examples and 2 comparative examples disclosed in Patent CN111647790B, it can be inferred that since homogenization treatment was not carried out, a large number of coarse NbC carbides exist in the microstructure, which is not conducive to the sodium corrosion resistance and neutron irradiation resistance. At the same time, due to the poor design of the composition (Nb content / C content and the value of Nb content × C content) and the preparation process, after the alloy is cooled by furnace cooling at 1140 °C for 30 h or aged at 600 °C for 5000 h, it is very difficult for the characteristic parameters such as the grain growth degree, the precipitates in the grain boundaries and within the grains, and the total proportion of ∑≤29 grain boundaries to meet the index requirements of the present invention, and it can be inferred therefrom that it cannot meet the service requirements of sodium-related moving parts. In addition, the tensile properties at 750 °C disclosed in this patent were obtained at a relatively low heat treatment temperature, and the microstructure uniformity is poor.

[0167] Examples 1 and Comparative Examples 1-3 are alloys with different Nb content / C content and Nb content × C content values, obtained after the same preparation process (not involving the process steps of carbide and grain boundary co-regulation). Example 2 is an alloy with the same Nb content / C content and Nb content × C content values as Example 1, obtained through multi-scale carbide and low-energy grain boundary co-regulation.

[0168] The compositions and microstructure characteristic parameters of the Fe-Ni-based superalloys prepared in Examples 1-2, 6 and Comparative Examples 1-3 were statistically analyzed, and the results are shown in Table 1.

[0169] Table 1:

[0170]

[0171] It can be seen that after cooling by furnace cooling at 1140 °C for 30 h, the alloys of Example 2 and Example 6 have excellent high-temperature grain stability, with a very low grain growth degree and a uniform grain size distribution, indicating that the effect of introducing low-energy special grain boundaries is obvious; while the grain size of the alloy in Example 1 increases significantly and the uniformity is poor. For the alloys in Comparative Examples 1 and 2, while the grains grow significantly, a large amount of Cr-rich brittle phases will precipitate at the grain boundaries. Although the number of precipitates at the grain boundaries in Comparative Example 3 is small, the size is significantly larger than that of the precipitates in Examples 1, 2 and 6. The above results are as Figure 5 shown.

[0172] The tensile properties and room temperature impact properties of the iron-nickel-based high-temperature alloys prepared in Examples 1-2, 6 and Comparative Examples 1-3 were tested under different conditions. The results are shown in Tables 2 and 3.

[0173] Table 2:

[0174]

[0175] It can be seen that the comparison example 1 does not meet the requirements because the Nb content / C content and Nb content × C content values ​​do not meet the requirements, and the strength and impact toughness do not meet the index requirements; the comparison example 2 has a low Nb content / C content, and the grain boundary is severely degraded after two high-temperature heat processes, and a large amount of Cr-rich brittle hard phase is precipitated, and the impact performance is low; the comparison example 3 has a high Nb content / C content and Nb content × C content, and a large amount of Nb-rich brittle hard phase is distributed in the grain boundary and in the grain, and the impact performance is low. The corresponding grain boundary structure after aging at 600℃ for 5000h is shown in the figure. Figure 6 As shown, no obvious phase precipitation behavior was observed in the grain boundaries and in the grains of the alloy of Example 1, and the high-temperature microstructure stability was excellent for a long time. Therefore, it is reasonable to coordinate the multi-scale carbides and low-energy grain boundaries based on the alloy composition in Example 1, which can further improve the thermal stability of the alloy.

[0176] Table 3:

[0177]

[0178] The high temperature durability of the iron-nickel based high temperature alloys prepared in Examples 1-2, 6 and Comparative Examples 1-3 was tested. The results are shown in Table 4.

[0179] Table 4:

[0180]

[0181] It can be seen that the alloy's long-lasting life can be significantly improved by the refined design of Nb content / C content and Nb content × C content. On this basis, the alloy's long-lasting life can be further improved by the coordinated regulation of multi-scale carbides and low-energy grain boundaries while slightly improving the yield strength. Compared with the alloy in comparative example 1, the alloy in Example 2 has an 8-fold longer long-lasting life, and performs well under the thermal-mechanical coupling of over-temperature service. In addition, when the total deformation during small deformation deep cold rolling is less than the critical deformation (Example 6), the grain size and TRD size of the alloy are both large, and the driving force for NbC precipitation is insufficient, which ultimately makes the alloy's yield strength at 750°C less than that of Example 1, indicating that the deformation of small deformation deep cold rolling needs to be precisely controlled within the range of 5% to 12% to achieve the optimal distribution of multi-scale carbides and low-energy grain boundaries.

[0182] The results of the examples show that based on the idea of synergistically regulating multi-scale carbides and low-energy grain boundaries, through refined chemical composition design and optimized thermo-mechanical treatment processes, the long-life iron-nickel-based superalloy with excellent thermal stability of the present invention has obtained both excellent high-temperature microstructure and performance stability, good sodium liquid corrosion resistance and neutron irradiation resistance, and can be used as a material for sodium-exposed moving parts in fast reactors to meet the use requirements of chromizing and nitriding processes and the subsequent extremely harsh in-reactor high-temperature and long-time service environment.

[0183] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor, characterized in that: The chemical composition by weight percentage is: C 0.03%~0.08%, Ni 35.0%~41.0%, Cr 14.0%~17.0%, Mo 3.5%~5.0%, Mn 1.0%~2.0%, Nb 0.2%~1.0%, B 0%~0.005%, Zr 0%~0.1%, Y 0%~0.07%, and the balance is Fe.

2. The long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor according to claim 1, characterized in that: Nb content and C content meet the following requirements: 11≤Nb / C≤13, 0.25×10 -5 ≤Nb×C≤0.35×10 -5 , Nb content and Mo content satisfy: Nb+Mo≥4.0wt.%.

3. A method for preparing the long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor according to claim 1 or 2, characterized in that: The steps include: (1) Prepare raw materials: prepare raw materials according to the chemical composition ratio of the alloy; (2) Dual vacuum smelting: The prepared alloy charge is subjected to dual vacuum smelting of vacuum induction melting and vacuum consumable remelting to obtain alloy ingots; (3) Homogenization treatment: After the riser of the alloy ingot is cut off, the temperature is raised to 1210℃~1230℃ and kept for 15h~30h; (4) Forging: The high-temperature homogenized ingot is kept at 1050°C to 1170°C for 2h to 4h and then forged to obtain a forging blank; (5) Hot rolling: the forged billet is kept at 1050°C to 1170°C for 2h to 4h and then hot rolled to obtain a hot rolled plate; (6) Solution treatment: Place the hot-rolled plate in a non-vacuum muffle furnace, keep it at 1100°C to 1150°C for 30 min to 60 min, and then air cool it; (7) Small deformation deep cold rolling: After the solution treatment, the upper and lower surfaces of the plate are polished and then deep cold rolled. Before rolling on a two-roll cold rolling mill, the plate is immersed in liquid nitrogen. The total deformation is controlled at 5% to 12%, and the number of rolling passes is controlled at 1 to 10 times to obtain a deep cold rolled plate. (8) Two-stage heat treatment: The cold-rolled sheet is placed in a non-vacuum muffle furnace, first kept at 1100℃~1150℃ for 1h~10h, and then cooled to 900℃~1000℃ with the furnace and kept at this temperature for 0.5h~4h.

4. The method for preparing a long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor according to claim 3, characterized in that: Step (4) Forging: The high temperature homogenized ingot is forged at a strain rate of 0.01s -1 ~1.0s -1 , the engineering strain is above 60% and the final forging temperature is above 950℃.

5. The method for preparing a long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor according to claim 3, characterized in that: Step (5) hot rolling: the forging blank is hot rolled at a strain rate of 2.0 s -1 ~10s -1 , the engineering strain is above 70%, the final rolling temperature is above 950℃, and a hot-rolled plate with a thickness of 6mm to 12mm is obtained.

6. The method for preparing a long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor according to claim 3, characterized in that: Step (7) small deformation deep cold rolling: before rolling, the plate is immersed in liquid nitrogen for 1 hour to 2 hours. After each 1 to 2 rolling passes, the plate is immersed in liquid nitrogen again for 10 minutes to 30 minutes, and finally a deep cold rolled plate with a thickness of 5.70 mm to 11.40 mm is obtained.

7. The method for preparing a long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor according to claim 3, characterized in that: The total proportion of ∑≤29 grain boundaries in the prepared long-life iron-nickel-based high-temperature alloy for fast reactor with excellent thermal stability is not less than 70%, and the ratio between the twin-related area size and the grain size is not less than 3.

8. The method for preparing a long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor according to claim 3, characterized in that: The average grain size of the iron-nickel-based high-temperature alloy with excellent thermal stability and long life for fast reactor is no more than twice that after two-stage heat treatment after being kept at 1140°C for 30 hours.

9. The method for preparing a long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor according to claim 3, characterized in that: The prepared long-life iron-nickel-based high-temperature alloy for fast reactor with excellent thermal stability has an initial structure of austenite and NbC, NbC is uniformly dispersed in spherical / blocky shapes, and the single particle size of NbC is less than 2μm; the structure after being kept at 1140°C for 30 hours and furnace-cooled or aging at 600°C for 5000 hours is still austenite and NbC; after being kept at 1140°C for 30 hours and furnace-cooled or aging at 600°C for 5000 hours, the 750°C tensile properties of the alloy meet the following requirements: yield strength is not less than 120MPa, tensile strength is not less than 280MPa, elongation is not less than 50%; room temperature impact toughness is not less than 400J / cm 2 .

10. The method for preparing a long-life iron-nickel-based high-temperature alloy with excellent thermal stability for fast reactor according to claim 3, characterized in that: The obtained long-life iron-nickel-based high-temperature alloy for fast reactor has excellent thermal stability. After two-stage heat treatment, the alloy's 750°C / 135MPa endurance performance meets the following requirements: endurance life is not less than 180h, and elongation is not less than 70%.

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