Ultralow-temperature high-toughness non-magnetic special alloy and manufacturing method thereof

Abstract

The invention relates to an ultralow-temperature high-toughness non-magnetic special alloy and a manufacturing method thereof, and belongs to the technical field of ultralow-temperature high-toughness alloys. The special alloy comprises the following chemical components: less than or equal to 0.02% of C, less than or equal to 0.002% of N, less than or equal to 0.001% of O, less than or equal to 0.005% of P, less than or equal to 0.003% of S, less than or equal to 0.005% of B, less than or equal to 0.20% of Si, less than or equal to 0.06% of Mn, less than or equal to 0.05% of Cu, 18-22% of Cr, 55.0-58.0% of Ni, 2.5-3.5% of Nb, 0.8-1.2% of Al, 1.2-2.0% of Ti, 1.0-2.5% of Mo, less than or equal to 2ppm of H, less than or equal to 0.05% of Co and the balance of Fe. The special alloy has a'twin crystal + gamma 'phase' composite structure, so that the special alloy has excellent obdurability matching at ultralow temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of cryogenic high-strength and tough alloys, and particularly relates to a cryogenic high-strength and tough non-magnetic special alloy and a manufacturing method thereof. Background Art

[0002] In cryogenic engineering, engineering equipment mainly serves in an extremely low temperature environment of -269°C, which also poses more stringent requirements on the properties of structural materials. Coupled problems such as high strength and toughness, non-magnetism, etc. have become the core challenges in future material research and development. Taking the axial preloading mechanism of the new generation of fusion engineering test reactor as an example, as the key barrier for the safe operation of the central solenoid magnet, its service environment is ultra-low temperature (-269°C), strong magnetic field (19.6T), and large current (46.5kA). It is the main carrier bearing periodic electromagnetic cyclic stress shocks of tens of thousands of Newtons, and it is required to maintain a yield strength of more than 800 MPa in the full temperature range from room temperature to 4.2K, with an elongation of more than 20% and a fracture toughness of 130 MPa·m 1 / 2 at the same time.

[0003] However, traditional high-strength austenitic stainless steels (for example, Nitronic 50 has a room temperature yield strength of 380 MPa to 420 MPa, and a low temperature fracture toughness K IC at 4.2K: 130 - 160 MPa·m 1 / 2 )(AMS 5746E) obviously can no longer meet the requirements of the fusion device for the ultimate properties of materials. There is an urgent need for a cryogenic high-strength and tough non-magnetic special alloy to provide guarantee for major cryogenic engineering construction including nuclear fusion engineering.

[0004] Therefore, there is an urgent need for a cryogenic high-strength and tough non-magnetic special alloy to provide guarantee for major cryogenic engineering construction including nuclear fusion engineering. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a cryogenic high-strength and tough non-magnetic special alloy and a manufacturing method thereof, so that the special alloy has high strength and toughness.

[0006] On the one hand, the present invention provides a cryogenic high-strength and tough non-magnetic special alloy. By mass percentage, its chemical composition is C: ≤0.02%, N: ≤0.002%, O: ≤0.001%, P: ≤0.005%, S: ≤0.003%, B: ≤0.005%, Si: ≤0.20%, Mn: ≤0.06%, Cu: ≤0.05%, Cr: 18 - 22%, Ni: 55.0 - 58.0%, Nb: 2.5 - 3.5%, Al: 0.8 - 1.2%, Ti: 1.2 - 2.0%, Mo: 1.0 - 2.5%, H: ≤2 ppm, Co: ≤0.05%, and the balance is Fe and unavoidable impurities.

[0007] Furthermore, the chemical composition of the special alloy is as follows: C: ≤0.01%, N: ≤0.001%, O: ≤0.0008%, P: ≤0.005%, S: ≤0.003%, B: ≤0.004%, Si: ≤0.10%, Mn: ≤0.02%, Cu: ≤0.03%, Cr: 19 - 21%, Ni: 56.0 - 57.0%, Nb: 3.0 - 3.5%, Al: 1.0 - 1.2%, Ti: 1.7 - 2.0%, Mo: 1.8 - 2.5%, H: ≤1 ppm, Co: ≤0.03%, and the balance is Fe and unavoidable impurities.

[0008] Furthermore, at room temperature, the yield strength of the special alloy is ≥800 MPa, and the elongation after fracture is ≥25%.

[0009] Furthermore, at the liquid helium temperature of -269 °C, the fracture toughness of the special alloy is ≥200 MPa·m 1 / 2 。

[0010] Furthermore, the inside of the special alloy is a twin + γ' phase composite structure, the matrix is austenite, and there is no M 23 C6 carbide.

[0011] On the other hand, the present invention provides a method for preparing an ultra-low temperature high-strength and tough non-magnetic special alloy, including the following steps: S1: Smelting process, proportioning according to the composition, and using vacuum induction and vacuum consumable double melting to obtain an ingot; S2: Forging process, subjecting the obtained ingot to high-temperature diffusion, and then performing cogging forging to obtain a forged blank; S3: Rolling process, heating the obtained forged blank, and then performing rolling to obtain a rolled blank; S4: Heat treatment process, subjecting the obtained rolled blank to heat treatment, and the heat treatment includes solution treatment and aging treatment to obtain an ultra-low temperature high-strength and tough non-magnetic special alloy.

[0012] Furthermore, in step S1, during the vacuum consumable process, the consumable melting rate is 4.0 - 6.5 kg / min.

[0013] Furthermore, in step S2, the high-temperature diffusion temperature is 1150 - 1200 °C, the cogging forging temperature is 1080 - 1120 °C, and the final forging temperature is 900 - 950 °C.

[0014] Furthermore, in step S3, the pre-rolling heating temperature is 1100 - 1180 °C, the starting rolling temperature is 1050 - 1090 °C, and the final rolling temperature is 880 - 930 °C.

[0015] Further, the solution treatment temperature is 980 - 1050 °C, and the holding time is 1 - 3 h; water quenching or oil quenching to room temperature; The aging treatment temperature is 700 °C - 750 °C, and the holding time is 15 - 25 h.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. In the present invention, the special alloy is a nickel - iron - based precipitation - strengthened alloy. Through the mutual cooperation of components, especially elements such as Ni / Ti / Al, by controlling the Nb content to adjust the stacking fault energy of the alloy, the alloy has good strain - hardening ability without martensitic transformation; the obtained special alloy has a "twin + γ′ phase" composite structure, enabling it to have excellent strength - toughness matching at ultra - low temperatures. The room - temperature yield strength is ≥800 MPa, the elongation after fracture is ≥25%, and the fracture toughness at - 269 °C liquid helium temperature is ≥200 MPa·m 1 / 2 , and the relative permeability < 1.03; 2. In the present invention, the preparation method of the special alloy mainly includes processes such as smelting, forging, rolling, and heat treatment. Among them, the smelting process is vacuum induction and vacuum consumable double - melting smelting, achieving precise control of ultra - low carbon (≤0.02%), ultra - low oxygen (≤0.001%), and ultra - low nitrogen (≤0.002%) after smelting; the heat treatment includes solution treatment and aging treatment, and it is necessary to strictly control the solution treatment temperature at 980 - 1050 °C, the holding time at 1 - 3 h; water quenching or oil quenching to room temperature; the aging treatment temperature is 700 °C - 750 °C, and the holding time is 15 - 25 h, enabling it to have excellent strength - toughness matching at ultra - low temperatures; 3. The special alloy of the present invention has high strength and toughness, can be directly applied to fasteners or structural components for fusion reactor superconducting magnets, and can also be extended and applied to other related fields such as high - strength and tough non - magnetic special alloy components required in ultra - low temperature engineering, having broad market prospects.

[0017] In the present invention, the above - mentioned technical solutions can also be combined with each other to achieve more preferred combined solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can be made obvious from the description, or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained from the content specifically pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings are only for the purpose of showing specific embodiments, and are not considered as a limitation of the present invention. Throughout the drawings, the same reference signs represent the same components; Figure 1 It is the micro - structure diagram of the tensile specimen of the special alloy obtained in Example 1 at - 269 °C liquid helium temperature; Figure 2 The metallographic photograph of the special alloy obtained in Example 2; Figure 3 The metallographic photograph of the special alloy obtained in Example 5; Figure 4 The microstructural diagram of the fracture surface after room-temperature tensile test of the special alloy obtained in Example 3; Figure 5 is Figure 4 The high-magnification microstructural diagram of the red box area in Specific Embodiments

[0019] The preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. The accompanying drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0020] Taking the BEST axial preloading mechanism as an example, as a key barrier for the safe operation of CS magnets, its service environment is ultra-low temperature (-269 °C), strong magnetic field (19.6 T), and large current (46.5 kA). It is the main carrier bearing cyclic electromagnetic stress shocks of tens of thousands of Newtons, and is required to maintain a yield strength of more than 800 MPa in the full temperature range from room temperature to 4.2 K, and also has an elongation of more than 20% and a fracture toughness of 130 MPa·m 1 / 2 Traditional high-strength austenitic stainless steels (for example, Nitronic 50 has a room-temperature yield strength of 380 MPa to 420 MPa, and a low-temperature fracture toughness K IC : 130 - 160 MPa·m 1 / 2 )(AMS 5746E) can obviously no longer meet the requirements of the fusion device for the ultimate performance of materials.

[0021] Therefore, the present invention provides a special alloy with ultra-low temperature high strength and toughness and non-magnetic properties. By mass percentage, its chemical composition is C: ≤0.02%, N: ≤0.002%, O: ≤0.001%, P: ≤0.005%, S: ≤0.003%, B: ≤0.005%, Si: ≤0.20%, Mn: ≤0.06%, Cu: ≤0.05%, Cr: 18 - 22%, Ni: 55.0 - 58.0%, Nb: 2.5 - 3.5%, Al: 0.8 - 1.2%, Ti: 1.2 - 2.0%, Mo: 1.0 - 2.5%, H: ≤2 ppm, Co: ≤0.05%, and the balance is Fe and inevitable impurities.

[0022] Compared with the prior art, in the present invention, the special alloy is a nickel-iron-based precipitation-strengthened alloy. Through the mutual cooperation of components, especially elements such as Ni / Ti / Al, the stacking fault energy of the alloy is adjusted by controlling the Nb content, so that the alloy has good strain hardening ability without martensitic transformation; the obtained special alloy has a "twin + γ' phase" composite structure, enabling it to have excellent strength-ductility matching at ultra-low temperatures, with a room-temperature yield strength ≥ 800 MPa, an elongation after fracture ≥ 25%, and a fracture toughness ≥ 200 MPa·m at the liquid helium temperature of -269 °C 1 / 2 , and the relative magnetic permeability < 1.03. The ultra-low temperature high-strength and tough non-magnetic special alloy of the present invention can be directly applied to the structural parts and fasteners for superconducting magnets of fusion reactors, and can also be widely applied to the structural parts and fasteners of major equipment such as superconducting accelerators, deep space exploration, and high-energy particle cooling systems, with very broad social benefits and market prospects.

[0023] The functions and ratios of the elements in the present invention are as follows: Carbon: Carbon is a strong austenite-forming and stabilizing element and an austenite-expanding element in nickel-iron-based precipitation-strengthened alloys, and is also the main element for solid solution strengthening. However, while increasing the strength, it will damage the plasticity, toughness, and weldability of the alloy. In addition, the presence of carbon elements in the alloy will cause harmful carbides to precipitate during aging, seriously reducing the ultra-low temperature plasticity and toughness of the alloy. Therefore, an ultra-low carbon content needs to be controlled in the alloy of the present invention. Considering comprehensively, the carbon in the alloy of the present invention is controlled within 0.02%.

[0024] Nitrogen: For the single-phase austenitic nickel-iron-based alloy of the present invention, the advantage of ultra-low nitrogen is that it can significantly improve the plasticity and toughness of the alloy. Although the solid solution strengthening effect is significant, this alloy contains elements such as Al and Ti, which are prone to form inclusions such as TiN and AlN, thereby significantly reducing the plasticity and toughness, especially the low-temperature plasticity and toughness. Therefore, the mass percentage content of nitrogen in the present invention is controlled within 0.002%.

[0025] Chromium: Chromium is one of the important alloying elements to improve the corrosion resistance of the alloy. As the chromium content increases, the intergranular corrosion resistance is significantly improved. At the same time, the presence of chromium elements can also improve the tempering resistance to maintain the dislocation strengthening and solid solution strengthening effects. In addition, chromium can significantly reduce the magnetic permeability of the alloy. In order to obtain non-magnetic properties, the mass percentage content range of chromium in the present invention is controlled to be 18 - 22%.

[0026] Nickel: Nickel is an important alloying element to stabilize the austenite phase, which can expand the austenite phase region and inhibit the formation of high-temperature δ-Fe at the same time. In addition, nickel can improve the ultra-low temperature performance of nickel-iron-based superalloys, and the low-temperature toughness is significantly improved with the increase of nickel. Considering comprehensively, the mass percentage content range of nickel in the present invention is controlled to be 55.0 - 58.0%.

[0027] Manganese: Manganese is also an austenite-forming element. At the same time, manganese can reduce the critical cooling rate during quenching, thereby effectively improving the hardenability and wear resistance of the alloy. However, excessive Mn will cause a significant decrease in the high-temperature creep life and plasticity of the alloy. Considering comprehensively, the mass percentage content of manganese in the present invention is controlled within 0.06%.

[0028] Silicon: Silicon mainly improves the oxidation resistance in the alloy. Since the alloy of the present invention selects pure metal materials and adopts the double ultra-pure smelting process of vacuum induction furnace + vacuum consumable, it is not necessary to add too much silicon for deoxidation. In addition, silicon is an element that promotes the formation of ferrite and will seriously damage the ultra-low temperature plasticity and toughness of the alloy. Therefore, it needs to be strictly controlled. Considering the above, the mass percentage content of silicon in the alloy of the present invention is controlled within 0.20%.

[0029] Phosphorus and sulfur: Impurity elements such as phosphorus and sulfur in steel significantly reduce the plasticity, toughness and welding performance. Since the alloy of the present invention adopts the double ultra-pure smelting process of vacuum induction furnace + vacuum consumable and selects pure metal materials for smelting, the mass percentage contents of phosphorus and sulfur are respectively controlled within 0.005% and 0.003%.

[0030] Oxygen: Oxygen is a harmful element in steel. Oxygen mainly exists in the form of various inclusions, seriously reducing the processing performance, plasticity, toughness and fatigue performance of steel. Considering the above, the oxygen in the alloy of the present invention is controlled within 0.001%.

[0031] Boron: Boron plays a role in enhancing the high-temperature creep performance in nickel-based superalloys. However, too high a content will lead to grain boundary segregation and solidification segregation. Therefore, the mass percentage content of boron in the alloy of the present invention is controlled within 0.005%.

[0032] Niobium: Niobium plays an obvious solid solution strengthening role in the γ matrix and exists as a precipitation strengthening element in γ′, which can greatly improve the strength of the alloy. It should be noted that niobium can also reduce the stacking fault energy of the alloy, thereby improving the ultra-low temperature strength and plasticity of nickel-based superalloys. Niobium is also a carbide-forming element. Too high a niobium content will cause the precipitation of Laves phase, seriously damaging the oxidation resistance and corrosion resistance of the alloy. Considering comprehensively, the mass percentage content range of niobium in the present invention is controlled at 2.5 - 3.5%.

[0033] Copper: The addition of copper can improve its strength and corrosion resistance, but at the same time it will also reduce its oxidation resistance. Therefore, the copper content in the steel of the present invention is controlled within 0.05%.

[0034] Aluminum: As one of the main forming elements of the γ'-phase, increasing the aluminum content can not only increase the volume fraction of the γ'-phase, but also form a dense oxide film, thereby improving the strength and oxidation resistance of the alloy. In addition, increasing the aluminum content will promote the precipitation of AlN, which will seriously damage the plasticity and toughness of the alloy. Considering comprehensively, the mass percentage range of aluminum controlled in the present invention is 0.8 - 1.2%.

[0035] Titanium: Titanium is also one of the main forming elements of the γ'-phase. The alloy forms Ni3Ti at 650 - 900 °C, thereby improving the strength of the alloy. However, an excessive Ti / Al ratio will lead to the precipitation of the harmful phase η-Ni3Ti, which will seriously damage the ultra-low temperature plasticity and toughness of the alloy. Considering comprehensively, the mass percentage range of titanium controlled in the present invention is 1.2 - 2.0%.

[0036] Molybdenum: Molybdenum can solid-solution strengthen the alloy matrix and improve the high-temperature strength of the alloy. At high temperatures, this helps to resist the tensile stress during the formation of thermal cracks and reduce the tendency of thermal crack generation. In addition, the addition of molybdenum will change the electron cloud distribution and crystal structure of the alloy, causing changes in the magnetic domain structure inside the alloy and making the movement of magnetic domain walls difficult, thereby reducing the magnetic permeability of the alloy. Considering comprehensively, the mass percentage range of molybdenum controlled in the present invention is 1.0 - 2.5%.

[0037] Cobalt: As an austenite stabilizing element, cobalt dissolved in the matrix can improve the high-temperature strength and creep resistance of the material. Excessive cobalt may interfere with austenite stability and promote the precipitation of brittle intermetallic phases (such as σ-phase), resulting in embrittlement of the material at high temperatures. Therefore, the cobalt content in the alloy of the present invention must be strictly controlled within 0.05%.

[0038] Hydrogen: Hydrogen is a harmful element in steel, which will cause hydrogen-induced cracking and brittle fracture, seriously reducing the ductility and toughness of the steel. Therefore, the hydrogen content in the alloy of the present invention must be strictly controlled within 2 ppm.

[0039] Specifically, the chemical composition of the special alloy is C: ≤0.01%, N: ≤0.001%, O: ≤0.0008%, P: ≤0.005%, S: ≤0.003%, B: ≤0.004%, Si: ≤0.10%, Mn: ≤0.02%, Cu: ≤0.03%, Cr: 19 - 21%, Ni: 56.0 - 57.0%, Nb: 3.0 - 3.5%, Al: 1.0 - 1.2%, Ti: 1.7 - 2.0%, Mo: 1.8 - 2.5%, H: ≤1 ppm, Co: ≤0.03%, and the balance is Fe and unavoidable impurities.

[0040] Preferably, the chemical composition of the special alloy is as follows: C: 0.0025 - 0.0046%, N: 0.0006 - 0.0008%, O: 0.0005 - 0.0008%, P: ≤0.005%, S: ≤0.003%, B: 0.0006 - 0.004%, Si: 0.005 - 0.10%, Mn: 0.0022 - 0.0092%, Cu: 0.012 - 0.021%, Cr: 19 - 21%, Ni: 56.0 - 57.0%, Nb: 3.0 - 3.5%, Al: 1.0 - 1.2%, Ti: 1.7 - 2.0%, Mo: 1.95 - 2.05%, H: ≤1 ppm, Co: ≤0.022%, and the balance is Fe and inevitable impurities.

[0041] The present invention also provides a preparation method of a super-low temperature high-strength and tough non-magnetic special alloy, which includes the following steps: S1: Smelting process. According to the composition, batching is carried out, and vacuum induction and vacuum consumable double melting are adopted to obtain an ingot. S2: Forging process. The obtained ingot is subjected to high-temperature diffusion, and then cogging forging is carried out to obtain a forging blank. S3: Rolling process. The obtained forging blank is heated and then rolled to obtain a rolled blank. S4: Heat treatment process. The obtained rolled blank is subjected to heat treatment, and the heat treatment includes solution treatment and aging treatment to obtain a super-low temperature high-strength and tough non-magnetic special alloy.

[0042] Compared with the prior art, in the present invention, the preparation method of the special alloy mainly includes processes such as smelting, forging, rolling and heat treatment. Among them, the smelting process is vacuum induction and vacuum consumable double melting. After smelting, precise control of ultra-low carbon (≤0.02%), ultra-low oxygen (≤0.001%) and ultra-low nitrogen (≤0.002%) is achieved, enabling it to have excellent strength and toughness matching at super-low temperatures.

[0043] Specifically, in step S1, during the vacuum consumable process, the consumable melting rate is 4.0 - 6.5 kg / min.

[0044] It should be noted that the smelting adopts a double melting process of a vacuum induction furnace + a vacuum consumable furnace. The smelting preferably includes vacuum induction smelting and vacuum consumable in sequence. The raw materials are pure metal materials and returned materials from Benxi Steel; the vacuum induction casting electrode is φ420 - φ600 mm; the vacuum consumable remelting is φ490 mm - φ660 mm, and helium cooling is adopted, with a consumable melting rate of 4.0 - 6.5 kg / min.

[0045] Specifically, in step S2, the high-temperature diffusion temperature is 1150 - 1200 °C, the cogging forging temperature is 1080 - 1120 °C, and the final forging temperature is 900 - 950 °C.

[0046] It should be noted that forging can refine the grain size through the dynamic recrystallization process, reduce the density of grain boundary defects, and at the same time eliminate the pores and looseness in the as-cast structure, significantly improving the material density. In addition, the plastic deformation during forging promotes the uniform distribution of alloying elements, eliminates dendritic segregation, and optimizes the size and distribution of γ'-strengthening phases.

[0047] In the present invention, the temperature of high-temperature diffusion can be 1150 °C, 1155 °C, 1160 °C, 1165 °C, 1170 °C, 1175 °C, 1180 °C, 1185 °C, 1190 °C, 1195 °C or 1200 °C.

[0048] In the present invention, the temperature of cogging forging can be 1080 °C, 1085 °C, 1090 °C, 1095 °C, 1100 °C, 1105 °C, 1110 °C, 1115 °C or 1120 °C.

[0049] In the present invention, the finish forging temperature can be 900 °C, 910 °C, 915 °C, 920 °C, 925 °C, 930 °C, 935 °C, 940 °C, 945 °C or 950 °C.

[0050] Specifically, in step S3, the pre-rolling heating temperature is 1100 - 1180 °C, the start-rolling temperature is 1050 - 1090 °C, and the finish-rolling temperature is 880 - 930 °C.

[0051] It should be noted that hot rolling promotes the occurrence of dynamic recrystallization through high-temperature plastic deformation, significantly refining the grains and improving the alloy strength; at the same time, it eliminates defects such as pores and shrinkage porosity in the as-cast structure, improving the material density. When the start-rolling temperature is too high, it will cause coarse grains and reduce the strength, and when it is too low, it will cause coarsening of the grain boundary precipitates.

[0052] In the present invention, the pre-rolling heating temperature can be 1100 °C, 1105 °C, 1110 °C, 1115 °C, 1120 °C, 1125 °C, 1130 °C, 1135 °C, 1140 °C, 1145 °C, 1150 °C, 1160 °C, 1170 °C, 1175 °C or 1180 °C.

[0053] In the present invention, the start-rolling temperature is 1050 °C, 1055 °C, 1060 °C, 1065 °C, 1070 °C, 1075 °C, 1080 °C, 1085 °C or 1090 °C.

[0054] In the present invention, the finish-rolling temperature is 880 °C, 885 °C, 890 °C, 895 °C, 900 °C, 910 °C, 915 °C, 920 °C, 925 °C or 930 °C.

[0055] Specifically, the solution treatment temperature is 980 - 1050°C, and the holding time is 1 - 3 h; water quenching or oil quenching to room temperature; The aging treatment temperature is 700°C - 750°C, and the holding time is 15 - 25 h.

[0056] It should be noted that too high aging temperature will lead to coarsening of the precipitation phase, reducing the strengthening effect, and too low aging temperature will result in insufficient precipitation, thereby reducing the performance of the alloy.

[0057] In the present invention, solution treatment is required after rolling. The solution temperature is controlled to be 980 - 1050°C, which can be 980°C, 990°C, 995°C, 1000°C, 1010°C, 1020°C, 1030°C, 1030°C, 1040°C or 1050°C.

[0058] In the present invention, the aging treatment temperature can be 700°C, 710°C, 720°C, 730°C, 740°C or 750°C.

[0059] Specifically, at room temperature, the yield strength of the special alloy is ≥800 MPa, and the elongation after fracture is ≥25%. At the liquid helium temperature of -269°C, the fracture toughness of the special alloy is ≥200 MPa·m 1 / 2 。

[0060] Specifically, the special alloy has a twin + γ' phase composite structure inside, the matrix is austenite, and there is no M 23 C6 carbide.

[0061] It should be noted that the special alloy of the present invention has high strength and toughness, can be directly applied to fasteners or structural parts for fusion reactor superconducting magnets, and can also be popularized and applied to other related fields such as high-strength and tough non-magnetic special alloy parts required in cryogenic engineering, and has broad market prospects.

[0062] To describe the present invention more clearly, it is further illustrated by the following examples and comparative examples.

[0063] Example 1 A preparation method of a cryogenic high-strength and tough non-magnetic special alloy, comprising the following steps: S1: Smelting process, batching according to the composition, and adopting double-link smelting of vacuum induction and vacuum consumable (the consumable melting rate is 4.0 - 6.5 kg / min) to obtain an ingot; The composition of the ingot is shown in Table 1; S2: Forging process, subjecting the obtained ingot to high-temperature diffusion, and then performing cogging forging to obtain a forging blank; Among them, the high-temperature diffusion temperature is 1180°C; Among them, the cogging forging temperature is 1080°C; Among them, the finish forging temperature is 920 °C; S3: Rolling process, heating the obtained forging blank and then performing rolling to obtain a rolled blank; Among them, the temperature for heating the forging blank before rolling is 1150 °C; Among them, the rolling temperature is 1100 °C; Among them, the finish rolling temperature is 950 °C; S4: Heat treatment process, performing heat treatment on the obtained rolled blank, and the heat treatment includes solution treatment and aging treatment to obtain an ultra-low temperature high-strength and tough non-magnetic special alloy; Among them, solution treatment: the solution treatment temperature is 1040 °C, the solution holding time is 1 h, and water quenching (i.e., water cooling after holding) is performed; aging treatment: the aging treatment temperature is 700 °C, and the aging holding time is 20 h.

[0064] Table 1 Chemical compositions of Examples 1-3 (unit: wt%)

[0065] Table 2 Preparation parameters of Examples 1-3

[0066] Table 3 Heat treatment parameters of Examples 1-3

[0067] Example 4 The preparation process of Example 4 is generally the same as that of Example 1, except that in Example 4, the aging treatment temperature is 750 °C.

[0068] Example 5 The preparation process of Example 5 is generally the same as that of Example 2, except that in Example 5, the aging treatment temperature is 750 °C.

[0069] Example 6 The preparation process of Example 6 is generally the same as that of Example 3, except that in Example 6, the aging treatment temperature is 750 °C.

[0070] Comparative Example 1 The preparation process of Comparative Example 1 is generally the same as that of Example 1, except that in Comparative Example 1, the existing Nitronic 50 is used, and its composition is Mn: 5.0%, Cr: 22%, Ni: 15.0%, Mo: 2%, Nb: 0.1%, N: 0.30%, V: 0.20%.

[0071] Comparative Example 2 The preparation process of Comparative Example 2 is generally the same as that of Example 1, except that in Comparative Example 2, the aging treatment temperature is 770 °C.

[0072] Performance detection The above Examples 1-6 and Comparative Examples 1-2 were subjected to performance detection, mainly including tensile strength, yield strength, elongation and reduction of area at room temperature, and fracture toughness at -269°C. The detection results are shown in Table 4.

[0073] Table 4 Performance detection results

[0074] Combining Examples 1-6 and Comparative Examples 1-2 and referring to Table 4 and Figures 1-5 It can be seen that by using the components and preparation methods of Examples 1-6 of the present invention, which mainly include processes such as smelting, forging, rolling and heat treatment, the obtained special alloy has a "twin + γ' phase" composite structure, enabling it to have excellent strength and toughness matching at ultra-low temperatures. At room temperature, the tensile strength of the special alloy is 1143-1286 MPa, the yield strength is 800-977 MPa, the elongation after fracture is 25-31.5%, the reduction of area is 26-49%, and the fracture toughness at -269°C liquid helium temperature is 200-356 MPa·m 1 / 2 , and the relative magnetic permeability < 1.03.

[0075] Combining Examples 1-6 and Comparative Example 2 and referring to Figures 1-5 , the special alloy obtained in the present invention has a "twin + γ' phase" composite structure. From Figure 1 it can be seen that: a large number of twin structures are generated during the low-temperature tensile process, so the special alloy has excellent strength and plasticity at ultra-low temperatures. From Figure 2 and Figure 3 it can be seen that: the grain size distribution of the ultra-low temperature high-strength and tough non-magnetic special alloy is uniform. The microstructure is an austenite matrix without M 23 C6 carbide. From Figure 4 and Figure 5 it can be seen that: a large number of dimples exist in the cross-section microstructure of the special alloy after the tensile test, indicating that it is a ductile fracture.

[0076] The special alloys obtained in Comparative Example 2 and Example 1 both have a "twin + γ' phase" composite structure. However, due to the higher aging temperature in the preparation process of Comparative Example 2, the performance of the obtained alloy decreases and cannot meet higher requirements.

[0077] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A super-low-temperature high-strength and tough non-magnetic special alloy, characterized in that, By mass percentage, its chemical composition is C: ≤0.02%, N: ≤0.002%, O: ≤0.001%, P: ≤0.005%, S: ≤0.003%, B: ≤0.005%, Si: ≤0.20%, Mn: ≤0.06%, Cu: ≤0.05%, Cr: 18 - 22%, Ni: 55.0 - 58.0%, Nb: 2.5 - 3.5%, Al: 0.8 - 1.2%, Ti: 1.2 - 2.0%, Mo: 1.0 - 2.5%, H: ≤2 ppm, Co: ≤0.05%, and the balance is Fe and unavoidable impurities.

2. The cryogenic high-strength and tough non-magnetic special alloy according to claim 1, wherein The chemical composition of the special alloy is C: ≤0.01%, N: ≤0.001%, O: ≤0.0008%, P: ≤0.005%, S: ≤0.003%, B: ≤0.004%, Si: ≤0.10%, Mn: ≤0.02%, Cu: ≤0.03%, Cr: 19 - 21%, Ni: 56.0 - 57.0%, Nb: 3.0 - 3.5%, Al: 1.0 - 1.2%, Ti: 1.7 - 2.0%, Mo: 1.8 - 2.5%, H: ≤1 ppm, Co: ≤0.03%, and the balance is Fe and unavoidable impurities.

3. The cryogenic high-strength and tough non-magnetic special alloy according to claim 1 or 2, characterized in that, At room temperature, the yield strength of the special alloy is ≥800 MPa, and the elongation after fracture is ≥25%.

4. The cryogenic high-strength and tough non-magnetic special alloy according to claim 1 or 2, characterized in that, At the temperature of liquid helium of -269°C, the fracture toughness of the special alloy is ≥200 MPa·m 1 / 2 .

5. The cryogenic high-strength and tough non-magnetic special alloy according to claim 1 or 2, characterized in that, The special alloy has a composite structure of twins + γ' phase, the matrix is austenite, and there is no M 23 C6 carbide.

6. A method for preparing an ultra-low temperature high-strength and tough non-magnetic special alloy according to any one of claims 1-5, characterized in that, It includes the following steps: S1: Smelting process. According to the composition, batching is carried out, and vacuum induction and vacuum consumable double melting are used to obtain an ingot. S2: Forging process. The obtained ingot is subjected to high-temperature diffusion, and then cogging forging is carried out to obtain a forging blank. S3: Rolling process. The obtained forging blank is heated and then rolled to obtain a rolled blank. S4: Heat treatment process. The obtained rolled blank is heat-treated. The heat treatment includes solution treatment and aging treatment to obtain an ultra-low temperature high-strength and tough non-magnetic special alloy.

7. The preparation method of the ultra-low temperature high-strength and tough non-magnetic special alloy according to claim 6, characterized in that, In step S1, during the vacuum consumable process, the consumable melting rate is 4.0 - 6.5 kg / min.

8. The preparation method of the ultra-low temperature high-strength and tough non-magnetic special alloy according to claim 6, wherein, In step S2, the high-temperature diffusion temperature is 1150 - 1200 °C, the cogging forging temperature is 1080 - 1120 °C, and the final forging temperature is 900 - 950 °C.

9. The preparation method of the ultra-low temperature high-strength and tough non-magnetic special alloy according to claim 6, characterized in that, In step S3, the pre-rolling heating temperature is 1100 - 1180 °C, the starting rolling temperature is 1050 - 1090 °C, and the final rolling temperature is 880 - 930 °C.

10. The preparation method of the ultra-low temperature high-strength and tough non-magnetic special alloy according to claim 6, wherein, The temperature of the solution treatment is 980 - 1050 °C, and the holding time is 1 - 3 h; water quenching or oil quenching to room temperature; The temperature of the aging treatment is 700 °C - 750 °C, and the holding time is 15 - 25 h.

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