Ultra-low temperature, high strength and toughness non-magnetic special alloy and manufacturing method thereof

Abstract

The present invention relates to an ultra-low temperature, high-strength, and toughness non-magnetic special alloy and a manufacturing method thereof, belonging to the technical field of ultra-low temperature, high-strength, and toughness alloys. The chemical composition of the special alloy 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: ≤2ppm, Co: ≤0.05%, and the balance is Fe. The special alloy has a "twin + γ' phase" composite structure, which gives it excellent strength and toughness matching at ultra-low temperatures.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-low temperature high-strength and toughness alloys, and in particular to an ultra-low temperature high-strength and toughness 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℃, which also puts forward more stringent requirements on the performance of structural materials. The coupling problems of high strength and toughness and non-magnetism have become the core challenges of future material research and development. Taking the axial preload mechanism of the new generation fusion engineering test reactor as an example, as a key barrier to the safe operation of the central solenoid magnet, its service environment is ultra-low temperature (-269℃), strong magnetic field (19.6T), and large current (46.5kA). It is the main carrier of periodic electromagnetic cyclic stress impact of tens of thousands of kilonewtons. It is required to maintain a yield strength of more than 800MPa in the entire temperature range from room temperature to 4.2K, and have an elongation of more than 20% and a tensile strength of 130MPa·m 1 / 2 Fracture toughness.

[0003] However, conventional high-strength austenitic stainless steels (e.g. Nitronic 50 room temperature yield strength 380MPa~420MPa, 4.2K low temperature fracture toughness K IC :130~160MPa·m 1 / 2 ) (AMS 5746E) is obviously unable to meet the extreme performance requirements of materials for fusion devices. There is an urgent need for an ultra-low temperature, high strength and toughness non-magnetic special alloy to provide support for the construction of major low-temperature projects including nuclear fusion projects.

[0004] Therefore, there is an urgent need for a special ultra-low temperature, high strength and toughness non-magnetic alloy to provide support for the construction of major low-temperature projects including nuclear fusion projects. Summary of the Invention

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

[0006] On the one hand, the present invention provides an ultra-low temperature, high-strength and tough non-magnetic special alloy, whose chemical composition, calculated by mass percentage, 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: ≤2ppm, Co: ≤0.05%, and the balance is Fe and unavoidable impurities.

[0007] Furthermore, 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: ≤1ppm, 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 -269°C liquid helium temperature, the fracture toughness of the special alloy is ≥200MPa·m 1 / 2 .

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

[0011] In another aspect, the present invention provides a method for preparing an ultra-low temperature, high-strength, and high-toughness non-magnetic special alloy, comprising the following steps:

[0012] S1: Smelting process, the ingredients are prepared according to the composition, and vacuum induction and vacuum consumable double smelting are used to produce ingots;

[0013] S2: Forging process, the obtained ingot is subjected to high temperature diffusion, and then subjected to blank forging to obtain a forging blank;

[0014] S3: rolling process, heating the obtained forging billet and then rolling it to obtain a rolled billet;

[0015] S4: heat treatment process, heat treatment of the obtained rolled billet, the heat treatment including solution treatment and aging treatment, to obtain an ultra-low temperature high-strength and tough non-magnetic special alloy.

[0016] Furthermore, in step S1, during the vacuum consumable process, the consumable melting rate is 4.0 to 6.5 kg / min.

[0017] Furthermore, in step S2, the high-temperature diffusion temperature is 1150-1200°C, the blank forging temperature is 1080-1120°C, and the final forging temperature is 900-950°C.

[0018] Furthermore, in step S3, the heating temperature before rolling is 1100-1180°C, the start rolling temperature is 1050-1090°C, and the finish rolling temperature is 880-930°C.

[0019] Furthermore, the temperature of the solution treatment is 980-1050° C., the holding time is 1-3 hours; water quenching or oil quenching to room temperature;

[0020] The temperature of the aging treatment is 700° C. to 750° C., and the holding time is 15 to 25 hours.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] 1. In the present invention, the special alloy is a nickel-iron-based precipitation-strengthened alloy. By combining the components, especially the Ni / Ti / Al elements, and adjusting the stacking fault energy of the alloy by controlling the Nb content, the alloy has good strain hardening ability without undergoing martensitic transformation. The resulting special alloy has a "twin + γ' phase" composite structure, which enables it to have excellent strength and toughness matching at ultra-low temperatures, with a room temperature yield strength of ≥800MPa, an elongation after fracture of ≥25%, and a fracture toughness of ≥200MPa·m at a temperature of -269°C liquid helium. 1 / 2 , relative magnetic permeability <1.03;

[0023] 2. In the present invention, the preparation method of the special alloy mainly includes processes such as smelting, forging, rolling and heat treatment. The smelting process is vacuum induction and vacuum consumable double smelting, and after smelting, ultra-low carbon (≤0.02%), ultra-low oxygen (≤0.001%) and ultra-low nitrogen (≤0.002%) are precisely controlled; the medium heat treatment includes solution treatment and aging treatment, and the solution treatment temperature needs to be strictly controlled to be 980-1050°C and the holding time is 1-3h; water quenching or oil quenching to room temperature; the aging treatment temperature is 700-750°C and the holding time is 15-25h, so that it has excellent strength and toughness matching at ultra-low temperature;

[0024] 3. The special alloy of the present invention has high strength and toughness, and can be directly used in fasteners or structural parts for fusion reactor superconducting magnets. It can also be promoted and applied to other related fields such as high-strength and tough non-magnetic special alloy components required in ultra-low temperature engineering, and has broad market prospects.

[0025] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. Like reference symbols denote like components throughout the accompanying drawings.

[0027] Figure 1 This is a microstructure diagram of a tensile test specimen of the special alloy obtained in Example 1 at a liquid helium temperature of -269°C;

[0028] Figure 2 This is a metallographic photograph of the special alloy obtained in Example 2;

[0029] Figure 3 This is a metallographic photograph of the special alloy obtained in Example 5;

[0030] Figure 4 This is a microstructure diagram of the fracture surface of the special alloy obtained in Example 3 after room temperature stretching;

[0031] Figure 5 for Figure 4 High-magnification tissue image of the red box area. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0033] Taking the BEST axial preload mechanism as an example, as a key barrier to the safe operation of CS magnets, its service environment is ultra-low temperature (-269°C), strong magnetic field (19.6T), and large current (46.5kA). It is the main carrier of periodic electromagnetic cyclic stress shocks of tens of thousands of kilonewtons. It is required to maintain a yield strength of more than 800MPa in the entire temperature range from room temperature to 4.2K, an elongation of more than 20%, and an elongation of 130MPa·m 1 / 2 Fracture toughness. Traditional high-strength austenitic stainless steel (such as Nitronic 50 room temperature yield strength 380MPa~420MPa, 4.2K low temperature fracture toughness K IC :130~160MPa·m 1 / 2 ) (AMS 5746E) is obviously unable to meet the extreme performance requirements of materials for fusion devices.

[0034] Therefore, the present invention provides an ultra-low temperature, high-strength and tough non-magnetic special alloy, whose chemical composition, calculated by mass percentage, 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: ≤2ppm, Co: ≤0.05%, and the balance is Fe and unavoidable impurities.

[0035] Compared with the existing technology, the special alloy in the present invention is a nickel-iron-based precipitation-strengthened alloy. By combining the components, especially the elements Ni / Ti / Al, and adjusting the stacking fault energy of the alloy by controlling the Nb content, the alloy has good strain hardening ability without undergoing martensitic transformation. The obtained special alloy has a "twin + γ' phase" composite structure, which enables it to have excellent strength and toughness matching at ultra-low temperatures, with a room temperature yield strength of ≥800MPa, an elongation after fracture of ≥25%, and a fracture toughness of ≥200MPa·m at a liquid helium temperature of -269°C. 1 / 2 , with a relative magnetic permeability of less than 1.03. The ultra-low-temperature, high-strength, and tough, non-magnetic special alloy of the present invention can be directly applied to structural components and fasteners for superconducting magnets in fusion reactors. It can also be widely applied to structural components and fasteners for major equipment such as superconducting accelerators, deep space exploration, and high-energy particle cooling systems. It has broad social benefits and market prospects.

[0036] The role and proportion of each element of the present invention are as follows:

[0037] Carbon: Carbon strongly forms and stabilizes austenite in nickel-iron-based precipitation-strengthened alloys, expanding the austenite zone and contributing to solid solution strengthening. However, while increasing strength, it also compromises the alloy's ductility, toughness, and weldability. Furthermore, the presence of carbon in the alloy can lead to the precipitation of harmful carbides in the matrix during aging, severely reducing the alloy's ultra-low-temperature ductility and toughness. Therefore, the alloy of the present invention requires an ultra-low carbon content. Taking all factors into consideration, the carbon content of the alloy of the present invention is controlled within 0.02%.

[0038] Nitrogen: For the single-phase austenitic nickel-iron-based alloy of the present invention, the advantage of ultra-low nitrogen is that it significantly improves the alloy's plasticity and toughness. Although the solid solution strengthening effect is significant, the alloy contains Al and Ti elements, which easily form inclusions such as TiN and AlN, which in turn significantly reduce plasticity and toughness, especially low-temperature plasticity and toughness. Therefore, the mass percentage of nitrogen in the present invention is controlled within 0.002%.

[0039] Chromium: Chromium is a key alloying element that improves the corrosion resistance of alloys. As the chromium content increases, intergranular corrosion resistance significantly improves. The presence of chromium also enhances tempering resistance, maintaining dislocation strengthening and solid solution strengthening effects. Furthermore, chromium significantly reduces the magnetic permeability of the alloy. To achieve non-magnetic properties, the present invention controls the chromium content to 18-22% by weight.

[0040] Nickel: Nickel is a key alloying element for stabilizing the austenite phase, expanding the austenite region while suppressing the formation of high-temperature δ-Fe. Furthermore, nickel enhances the ultra-low-temperature performance of nickel-iron-based superalloys, significantly improving low-temperature toughness with increasing nickel content. Taking all factors into consideration, the present invention controls the nickel content by weight within the range of 55.0 to 58.0%.

[0041] Manganese: Manganese is also an austenite-forming element. It also reduces the critical cooling rate during quenching, effectively improving the alloy's hardenability and wear resistance. However, excessive amounts of Mn can significantly reduce the alloy's high-temperature durability and plasticity. For these reasons, the present invention limits the manganese content to less than 0.06% by weight.

[0042] Silicon: Silicon primarily enhances oxidation resistance in alloys. Because the alloys of this invention are made from pure metals and utilize a vacuum induction furnace and vacuum consumable dual-process ultrapure smelting, excessive silicon addition for deoxidation is unnecessary. Furthermore, silicon promotes ferrite formation, significantly impairing the alloy's ultra-low-temperature plasticity and toughness, thus requiring strict control. For these reasons, the mass percentage of silicon in the alloys of this invention is controlled within 0.20%.

[0043] Phosphorus and sulfur: Impurity elements such as phosphorus and sulfur in steel significantly reduce plastic toughness and welding performance. Since the alloy of the present invention adopts a vacuum induction furnace + vacuum consumable double ultra-pure smelting process and uses pure metal materials for smelting, the mass percentages of phosphorus and sulfur are controlled within 0.005% and 0.003% respectively.

[0044] Oxygen: Oxygen is a harmful element in steel. It exists primarily as various inclusions, severely reducing the steel's processability, plasticity, toughness, and fatigue properties. Taking all of the above into account, the oxygen content in the alloy of the present invention is controlled within 0.001%.

[0045] Boron: Boron plays a role in enhancing high-temperature creep properties in nickel-iron-based high-temperature alloys, but too high a content can lead to grain boundary segregation and solidification segregation. Therefore, the mass percentage of boron in the alloy of the present invention is controlled within 0.005%.

[0046] Niobium: Niobium significantly strengthens the γ matrix through solid solution strengthening and acts as a precipitation-strengthening element in the γ′ phase, significantly enhancing the alloy's strength. Notably, niobium also reduces the alloy's stacking fault energy, thereby improving the ultra-low-temperature strength and ductility of nickel-iron-based superalloys. Niobium is also a carbide-forming element. Excessive niobium content can induce Laves phase precipitation, severely impairing the alloy's oxidation and corrosion resistance. Taking all these factors into consideration, the present invention limits the niobium content to 2.5-3.5% by weight.

[0047] Copper: The addition of copper can improve its strength and corrosion resistance, but it also reduces its oxidation resistance. Therefore, the copper content in the steel of the present invention is controlled within 0.05%.

[0048] Aluminum: As one of the primary elements forming the γ′ phase, increasing its content not only increases the volume fraction of the γ′ phase but also forms a dense oxide film, thereby improving the alloy's strength and oxidation resistance. Furthermore, increasing the aluminum content promotes the precipitation of AlN, which can severely impair the alloy's plasticity and toughness. For these reasons, the aluminum content is controlled within the range of 0.8% to 1.2% by weight in the present invention.

[0049] Titanium: Titanium is also a major element in the formation of the γ′ phase. At 650-900°C, the alloy forms Ni₃Ti, which improves its strength. However, an excessively high Ti / Al ratio can lead to the precipitation of the detrimental η-Ni₃Ti phase, which can severely impair the alloy's ultra-low temperature ductility and toughness. For these reasons, the present invention controls the titanium content by weight within the range of 1.2-2.0%.

[0050] Molybdenum: Molybdenum solid-solution strengthens the alloy matrix, improving its high-temperature strength. At high temperatures, this helps resist the tensile stresses that cause hot cracks, reducing their tendency to form. Furthermore, the addition of molybdenum alters the alloy's electron cloud distribution and crystal structure, altering the internal magnetic domain structure and making domain wall movement more difficult, thereby reducing the alloy's magnetic permeability. Taking all these factors into consideration, the molybdenum content in this invention is controlled within a range of 1.0 to 2.5% by weight.

[0051] Cobalt: As an austenite-stabilizing element, cobalt, when dissolved in the matrix, improves the material's high-temperature strength and creep resistance. Excessive cobalt can interfere with austenite stability, promoting the precipitation of brittle intermetallic phases (such as sigma phase), leading to embrittlement at high temperatures. Therefore, the cobalt content in the alloy of this invention must be strictly controlled within 0.05%.

[0052] Hydrogen: Hydrogen is a harmful element in steel. It can cause hydrogen-induced cracking and brittle fracture, seriously reducing the toughness and plasticity of steel. Therefore, the hydrogen content in the alloy of the present invention must be strictly controlled within 2 ppm.

[0053] 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: ≤1ppm, Co: ≤0.03%, and the balance is Fe and unavoidable impurities.

[0054] Preferably, the chemical composition of the special alloy is 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: ≤1ppm, Co: ≤0.022%, and the balance is Fe and unavoidable impurities.

[0055] The present invention also provides a method for preparing an ultra-low temperature, high-strength, and high-toughness non-magnetic special alloy, comprising the following steps:

[0056] S1: Smelting process, the ingredients are prepared according to the composition, and vacuum induction and vacuum consumable double smelting are used to produce ingots;

[0057] S2: Forging process, the obtained ingot is subjected to high temperature diffusion, and then subjected to blank forging to obtain a forging blank;

[0058] S3: rolling process, heating the obtained forging billet and then rolling it to obtain a rolled billet;

[0059] S4: heat treatment process, heat treatment of the obtained rolled billet, the heat treatment including solution treatment and aging treatment, to obtain an ultra-low temperature high-strength and tough non-magnetic special alloy.

[0060] Compared with the existing technology, the preparation method of the special alloy in the present invention mainly includes processes such as smelting, forging, rolling and heat treatment. The smelting process is vacuum induction and vacuum consumable double smelting. After smelting, precise control of ultra-low carbon (≤0.02%), ultra-low oxygen (≤0.001%) and ultra-low nitrogen (≤0.002%) is achieved, so that it has excellent strength and toughness matching at ultra-low temperature.

[0061] Specifically, in step S1, during the vacuum consumable process, the consumable melting rate is 4.0-6.5 kg / min.

[0062] It should be noted that the smelting process utilizes a dual vacuum induction furnace and a vacuum consumable furnace, preferably sequentially performing vacuum induction smelting and vacuum consumable melting. Raw materials include pure metal and Benxi Steel return material; vacuum induction casting electrodes are 420-600mm in diameter; vacuum consumable remelting is performed in 490-660mm diameters with helium cooling, at a consumable melting rate of 4.0-6.5kg / min.

[0063] Specifically, in step S2, the high-temperature diffusion temperature is 1150-1200°C, the blank forging temperature is 1080-1120°C, and the final forging temperature is 900-950°C.

[0064] It should be noted that forging can refine grain size and reduce grain boundary defect density through the dynamic recrystallization process, while simultaneously eliminating porosity and looseness in the as-cast structure, significantly improving material density. Furthermore, plastic deformation during forging promotes the uniform distribution of alloying elements, eliminates dendritic segregation, and optimizes the size and distribution of the γ' strengthening phase.

[0065] In the present invention, the temperature of the high temperature diffusion may be 1150°C, 1155°C, 1160°C, 1165°C, 1170°C, 1175°C, 1180°C, 1185°C, 1190°C, 1195°C or 1200°C.

[0066] In the present invention, the temperature of the blank forging may be 1080°C, 1085°C, 1090°C, 1095°C, 1100°C, 1105°C, 1110°C, 1115°C or 1120°C.

[0067] In the present invention, the final forging temperature may be 900°C, 910°C, 915°C, 920°C, 925°C, 930°C, 935°C, 940°C, 945°C or 950°C.

[0068] Specifically, in step S3, the heating temperature before rolling is 1100-1180°C, the start rolling temperature is 1050-1090°C, and the finish rolling temperature is 880-930°C.

[0069] It should be noted that hot rolling promotes dynamic recrystallization through high-temperature plastic deformation, significantly refining the grains and improving the alloy's strength. It also eliminates defects such as porosity and shrinkage in the as-cast structure, increasing the material's density. When the starting rolling temperature is too high, the grains become coarse and the strength is reduced, while when the starting rolling temperature is too low, the grain boundaries become coarser.

[0070] In the present invention, the heating temperature before rolling may 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.

[0071] In the present invention, the starting rolling temperature is 1050°C, 1055°C, 1060°C, 1065°C, 1070°C, 1075°C, 1080°C, 1085°C or 1090°C.

[0072] In the present invention, the finishing rolling temperature is 880°C, 885°C, 890°C, 895°C, 900°C, 910°C, 915°C, 920°C, 925°C or 930°C.

[0073] Specifically, the temperature of the solution treatment is 980-1050° C., the holding time is 1-3 hours; water quenching or oil quenching to room temperature;

[0074] The temperature of the aging treatment is 700° C. to 750° C., and the holding time is 15 to 25 hours.

[0075] It should be noted that if the aging temperature is too high, the precipitation phase will coarsen and reduce the strengthening effect. If the aging temperature is too low, the precipitation will be insufficient, thereby reducing the performance of the alloy.

[0076] In the present invention, solution treatment is required after rolling, and 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.

[0077] In the present invention, the temperature of the aging treatment may be 700°C, 710°C, 720°C, 730°C, 740°C or 750°C.

[0078] Specifically, at room temperature, the yield strength of the special alloy is ≥800MPa, and the elongation after fracture is ≥25%. At -269℃ liquid helium temperature, the fracture toughness of the special alloy is ≥200MPa·m 1 / 2 .

[0079] Specifically, the special alloy has a twin + γ' phase composite structure, the matrix is ​​austenite, and there is no M 23 C6 carbide.

[0080] It should be noted that the special alloy of the present invention has high strength and toughness, and can be directly used in fasteners or structural parts for fusion reactor superconducting magnets. It can also be promoted and applied to other related fields such as high-strength and tough non-magnetic special alloy components required in ultra-low temperature engineering, and has broad market prospects.

[0081] In order to more clearly describe the present invention, it is further illustrated by the following examples and comparative examples.

[0082] Example 1

[0083] The preparation method of the ultra-low temperature high-strength and high-toughness non-magnetic special alloy comprises the following steps:

[0084] S1: Smelting process, the ingredients are prepared according to the composition, and the ingot is produced by vacuum induction and vacuum consumable (consumable melting rate is 4.0-6.5 kg / min) double smelting;

[0085] The composition of the ingot is shown in Table 1;

[0086] S2: Forging process, the obtained ingot is subjected to high temperature diffusion, and then subjected to blank forging to obtain a forging blank;

[0087] The temperature of high temperature diffusion is 1180℃;

[0088] The temperature of blank forging is 1080℃;

[0089] The final forging temperature is 920℃;

[0090] S3: rolling process, heating the obtained forging billet and then rolling it to obtain a rolled billet;

[0091] The temperature of heating the forging billet before rolling is 1150℃;

[0092] The rolling temperature is 1100℃;

[0093] The final rolling temperature is 950℃;

[0094] S4: heat treatment process, heat treatment of the obtained rolled billet, wherein the heat treatment includes solution treatment and aging treatment, to obtain an ultra-low temperature high-strength and tough non-magnetic special alloy;

[0095] The solution treatment includes: the solution treatment temperature is 1040℃, the solution holding time is 1h, and water quenching (i.e. water cooling after holding); the aging treatment includes: the aging treatment temperature is 700℃, and the aging holding time is 20h.

[0096] Table 1 Chemical composition of Examples 1-3 (unit: wt%)

[0097]

[0098] Table 2 Preparation parameters of Examples 1-3

[0099]

[0100] Table 3 Heat treatment parameters of Examples 1-3

[0101]

[0102] Example 4

[0103] The preparation process of Example 4 is substantially the same as that of Example 1, except that the aging treatment temperature in Example 4 is 750°C.

[0104] Example 5

[0105] The preparation process of Example 5 is substantially the same as that of Example 2, except that the aging treatment temperature in Example 5 is 750°C.

[0106] Example 6

[0107] The preparation process of Example 6 is substantially the same as that of Example 3, except that the aging treatment temperature in Example 6 is 750°C.

[0108] Comparative Example 1

[0109] The preparation process of Comparative Example 1 is substantially the same as that of Example 1, except that the existing Nitronic 50 is used in Comparative Example 1, and its composition is Mn: 5.0%, Cr: 22%, Ni: 15.0%, Mo: 2%, Nb: 0.1%, N: 0.30%, and V: 0.20%.

[0110] Comparative Example 2

[0111] The preparation process of Comparative Example 2 is substantially the same as that of Example 1, except that the aging treatment temperature in Comparative Example 2 is 770°C.

[0112] Performance testing

[0113] The above Examples 1-6 and Comparative Examples 1-2 were subjected to performance tests, mainly including tensile strength, yield strength, elongation and cross-sectional shrinkage at room temperature, and fracture toughness at -269°C. The test results are shown in Table 4.

[0114] Table 4 Performance test results

[0115]

[0116] Combined with Examples 1-6 and Comparative Examples 1-2 and with reference to Tables 4 and Figure 1-5It can be seen that the compositions and preparation methods of Examples 1-6 of the present invention mainly include processes such as smelting, forging, rolling and heat treatment. The obtained special alloy has a "twin + γ' phase" composite structure, which enables it to have excellent strength and toughness matching at ultra-low temperatures. At room temperature, the special alloy has a tensile strength of 1143-1286 MPa, a yield strength of 800-977 MPa, an elongation after fracture of 25-31.5%, a cross-sectional reduction rate of 26-49%, and a fracture toughness of 200-356 MPa·m at a liquid helium temperature of -269°C. 1 / 2 , relative magnetic permeability <1.03.

[0117] Combined with Examples 1-6 and Comparative Example 2 Figure 1-5 The special alloy obtained in the present invention has a "twin + γ' phase" composite structure. Figure 1 It can be seen that a large number of twin structures are generated during the low-temperature stretching process, so the special alloy has excellent strength and plasticity at ultra-low temperatures. Figure 2 and Figure 3 It can be seen that the grain size of this ultra-low temperature, high strength and toughness non-magnetic special alloy is evenly distributed. The microstructure is austenite matrix, without M 23 C6 carbide. Figure 4 and Figure 5 It can be seen that there are a large number of dimples in the cross-section of special alloys after tensile testing, indicating that it is a ductile fracture.

[0118] The special alloys obtained in Comparative Example 2 and Example 1 both have a "twin + γ' phase" composite structure. However, due to the high aging temperature in the preparation process of Comparative Example 2, the performance of the obtained alloy is reduced and cannot meet higher requirements.

[0119] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. An ultra-low temperature, high strength and toughness non-magnetic special alloy, characterized in that: The chemical composition, in terms of mass percentage, is C: 0.0025-0.02%, N: 0.0006-0.002%, O: ≤0.001%, P: ≤0.005%, S: ≤0.003%, B: 0.0006-0.004%, Si: 0.005-0.20%, Mn: 0.0022-0.02%, Cu: 0.012-0.05%, 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: ≤2ppm, Co: ≤0.05%, and the balance is Fe and unavoidable impurities; Twins in special alloys Phase composite structure, the matrix is ​​austenite, and there is no M 23 C6 carbide; at -269℃ liquid helium temperature, the fracture toughness of the special alloy is ≥200MPa·m 1 / 2 , relative magnetic permeability <1.

03.

2. The ultra-low temperature, high strength and toughness non-magnetic special alloy according to claim 1, characterized in that: 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: ≤1ppm, Co: ≤0.03%, and the balance is Fe and unavoidable impurities.

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

4. A method for preparing the ultra-low temperature, high strength and toughness non-magnetic special alloy according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: Smelting process, the ingredients are prepared according to the composition, and vacuum induction and vacuum consumable double smelting are used to produce ingots; S2: Forging process, the obtained ingot is subjected to high temperature diffusion, and then subjected to blank forging to obtain a forging blank; S3: rolling process, heating the obtained forging billet and then rolling it to obtain a rolled billet; S4: heat treatment process, heat treatment of the obtained rolled billet, the heat treatment including solution treatment and aging treatment, to obtain an ultra-low temperature high-strength and tough non-magnetic special alloy.

5. The method for preparing the ultra-low temperature, high strength and toughness non-magnetic special alloy according to claim 4, characterized in that: In step S1, during the vacuum consumable process, the consumable melting rate is 4.0-6.5 kg / min.

6. The method for preparing the ultra-low temperature, high strength and toughness non-magnetic special alloy according to claim 4, characterized in that: In step S2, the high-temperature diffusion temperature is 1150-1200°C, the blank forging temperature is 1080-1120°C, and the final forging temperature is 900-950°C.

7. The method for preparing the ultra-low temperature, high strength and toughness non-magnetic special alloy according to claim 4, characterized in that: In step S3, the pre-rolling heating temperature is 1100-1180°C, the start rolling temperature is 1050-1090°C, and the final rolling temperature is 880-930°C.

8. The method for preparing the ultra-low temperature, high strength and toughness non-magnetic special alloy according to claim 4, characterized in that: The temperature of the solution treatment is 980-1050°C, and the holding time is 1-3 hours; water quenching or oil quenching to room temperature; The temperature of the aging treatment is 700° C. to 750° C., and the holding time is 15 to 25 hours.

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