A super-low temperature high-strength and tough non-magnetic stainless steel sheet applicable to -269°C and its manufacturing method

Abstract

The present invention relates to a super-ultra-low temperature high-strength and tough non-magnetic stainless steel sheet applicable to -269 °C and its manufacturing method, belonging to the technical field of high-strength stainless steel. The chemical composition of the high-strength and tough non-magnetic stainless steel sheet is: C ≤ 0.006%, N: 0.35 - 0.45%, O ≤ 0.0020%, P ≤ 0.010%, S ≤ 0.005%, Cr: 21.0 - 22.0%, Ni: 15.0 - 16.5%, Mo: 2.3 - 2.6%, Mn: 6.2 - 10.0%, Si ≤ 0.20%, Nb < 0.04%, V: 0.15 - 0.25%, Cu: 0.10 - 0.15%, Al ≤ 0.02%, Ti ≤ 0.02%, Co ≤ 0.05%. It is a new type of stainless steel with ultra-high strength, high toughness, complete austenite stability and low magnetic permeability at -269 °C.

Description

Technical Field

[0001] The present invention relates to the technical field of high-strength stainless steel, and particularly to a super-low temperature high-strength and tough non-magnetic stainless steel plate applicable to -269°C and a manufacturing method thereof. Background Art

[0002] Ultra-low temperature engineering is crucial for economic development and scientific and technological innovation. Among them, "large nuclear fusion devices" are the most exemplary ultra-low temperature projects, and they are major scientific devices related to energy security. The breakthrough of ultra-low temperature technology plays an irreplaceable supporting role in energy revolution (such as controllable nuclear fusion), frontier scientific devices (such as superconducting accelerators), and deep space exploration (such as cryogenic propulsion systems and high-energy particle cooling systems of spacecraft).

[0003] With the development of ultra-low temperature technology, traditional austenitic stainless steels (such as stainless steel of grade 316LN) are mainly used to prepare engineering equipment, which has good low-temperature stability. However, its yield strength at -269°C (~1000 MPa) and anti-sensitization ability can no longer meet the requirements of the ultimate performance of engineering equipment (such as the new generation of fusion devices), resulting in a sharp drop in the reliability of materials in deep low-temperature and strong magnetic field environments. With the development of technology, the invention patent with publication number CN117286426A discloses a high-strength non-magnetic austenitic stainless steel, which has good non-magnetic properties, and its yield strength at -269°C is between 1250 and 1420 MPa, and the tensile strength is between 1700 and 1831 MPa.

[0004] With the sharp increase in the complexity and performance requirements of engineering equipment in extremely low-temperature environments (-269°C), almost harsh requirements are put forward for structural materials. Existing materials or stainless steels cannot meet the requirements of ultra-high strength (yield strength ≥1500 MPa and tensile strength ≥1900 MPa at -269°C), high toughness, and non-magnetism. Therefore, there is an urgent need for a new type of stainless steel with ultra-high strength, high toughness, complete austenite stability, and low magnetic permeability at -269°C. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a super-low temperature high-strength and tough non-magnetic stainless steel plate applicable to -269°C and a manufacturing method thereof, which has high strength and toughness at -269°C and a relatively low relative magnetic permeability.

[0006] On the one hand, the present invention provides a high-strength and toughness non-magnetic stainless steel plate, whose chemical composition, measured by weight percentage, is: C≤0.006%, N: 0.35~0.45%, O≤0.0020%, P≤0.010%, S≤0.005%, Cr: 21.0~22.0%, Ni: 15.0~16.5%, Mo: 2.3~2.6%, Mn: 6.2~10.0%, Si≤0.20%, Nb<0.04%, V: 0.15~0.25%, Cu: 0.10~0.15%, Al≤0.02%, Ti≤0.02%, Co≤0.05%, and the balance is Fe and unavoidable impurities.

[0007] Furthermore, the chemical composition of the high-strength and toughness non-magnetic stainless steel plate is: C≤0.006%, N: 0.37~0.45%, O≤0.0020%, P≤0.010%, S≤0.005%, Cr: 21.0~21.5%, Ni: 15.0~15.4%, Mo: 2.3~2.5%, Mn: 7.0~10.0%, Si≤0.20%, Nb<0.04%, V: 0.15~0.19%, Cu: 0.10~0.15%, Al≤0.02%, Ti: 0.012~0.02%, Co: ≤0.04%, and the balance is Fe and unavoidable impurities.

[0008] Furthermore, at the ultra-low temperature of -269°C liquid helium, the yield strength of the stainless steel plate is above 1500MPa, the tensile strength is above 1900MPa, the elongation after fracture is above 30%, the V-type impact energy is 150~170J, and the fracture toughness is 160~200MPa·m 1 / 2 , and the relative magnetic permeability is less than 1.01.

[0009] Furthermore, the grain size grade of the stainless steel plate is 4-7.

[0010] On the other hand, the present invention provides a method for manufacturing the high-strength and toughness non-magnetic stainless steel sheet, comprising the following steps:

[0011] S1: The ingredients are prepared according to the alloy composition, and the electroslag ingot is obtained after electric furnace smelting and electroslag remelting;

[0012] S2: subjecting the electroslag ingot to high temperature diffusion and then forging to obtain a forging blank;

[0013] S3: rolling the obtained forging billet to obtain a rolled plate;

[0014] S4: Finally, the obtained rolled plate is subjected to a solid solution treatment to obtain a high-strength and tough non-magnetic stainless steel plate.

[0015] Furthermore, AOD and LF smelting are carried out after electric furnace smelting; the steel casting temperature is 1480 - 1520 °C.

[0016] Furthermore, during electroslag remelting, the slag system is a ternary slag system of CaF2 - Al2O3 - CaO, remelting is carried out under an argon protection atmosphere, and the ingot is removed more than 1 h after the remelting ends.

[0017] Furthermore, the temperature of the high - temperature diffusion is 1190 - 1210 °C. During the forging process, the starting forging temperature is ≥1050 °C, and the finishing forging temperature is ≥900 °C.

[0018] Furthermore, during the rolling process, the pre - rolling heat preservation temperature is 1160 - 1180 °C, the starting rolling temperature is ≥1050 °C, and the finishing rolling temperature is ≥900 °C.

[0019] Furthermore, the heat preservation temperature of the solution treatment is 1000 - 1100 °C, the heat preservation time is 30 - 150 min, and after the solution treatment, it is rapidly cooled to room temperature by water quenching.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. Through the design of alloy components, the present invention controls the C content to be less than 0.006%, the O content to be less than 0.002%; accurately controls the N content to be 0.35 - 0.45%; at the same time, it is necessary to strictly control the Mn content to be 6.2 - 10.0%, the Nb content to be less than 0.04%, and the Mo content to be 2.3 - 2.6%; restricts the contents of Ti and Al elements. Through the interaction between elements, it plays a role in solid solution strengthening and grain refinement, and at the same time significantly reduces the contents of niobium nitride, titanium nitride, and aluminum nitride in the stainless steel at high temperatures, ensuring the strength and toughness of the stainless steel sheet; at the ultra - low temperature of - 269 °C liquid helium temperature, the yield strength of the stainless steel sheet is above 1500 MPa, the tensile strength is above 1900 MPa, the elongation after fracture is above 30%, the V - notch impact energy is 150 - 170 J, and the fracture toughness is 160 - 200 MPa·m 1 / 2 , and the relative magnetic permeability < 1.01;

[0022] 2. On the basis of the compounding of alloy components, the present invention provides a preparation method for stainless steel sheets, mainly through processes such as melting, forging, rolling, and heat treatment of electric furnace and electroslag remelting. On the one hand, it can reduce production costs, use an electric furnace instead of an intermediate - frequency induction furnace without affecting the performance of the final stainless steel sheet; on the other hand, based on the coordinated control of composition - method - structure, through technical means such as high - nitrogen interstitial solid solution strengthening, fine - grain strengthening, and carbon / nitride precipitation strengthening, the yield strength of the steel of the present invention is higher than 1500 MPa at - 269 °C, and at the same time, the grain structure is uniform, the grains are refined, and it can reach 4 - 7 grades;

[0023] 3. The stainless steel sheet produced by the present invention has high strength and toughness, and is non-magnetic, and can fully withstand the use at the temperature of liquid helium at -296°C. Therefore, it can be used in the structural components of high magnetic field superconducting magnets, deep space exploration, and ultra-low temperature devices at the temperature of liquid helium at -296°C.

[0024] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification, or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained from the content specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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;

[0026] Figure 1 is the microstructural diagram of Example 1;

[0027] Figure 2 is the microstructural diagram of Example 2;

[0028] Figure 3 is the microstructural diagram of Example 4;

[0029] Figure 4 is the grain size diagram of Example 5;

[0030] Figure 5 is the microstructural characterization diagram of the fracture surface after the tensile test of Example 2 at -269°C;

[0031] Figure 6 is Figure 5 the enlarged view of area A in

[0032] Figure 7 is the microstructural characterization diagram of the fracture surface after the tensile test of Example 3 at -269°C;

[0033] Figure 8 is Figure 7 the enlarged view of area A in

[0034] Figure 9 is the physical drawing of the sheet of Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The preferred embodiments of the present invention will be specifically described below with reference to the drawings, in which the drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principle of the present invention, and are not used to limit the scope of the present invention.

[0036] Cryogenic engineering is crucial for economic development and scientific and technological innovation. With the development of cryogenic technology, traditional austenitic stainless steels (such as grade 316LN stainless steel) are mainly used to prepare engineering equipment or structural components for cryogenic use. 316LN stainless steel has good low-temperature stability, but its yield strength at -269 °C is about 1000 MPa. With the sharp increase in the complexity and performance requirements of engineering equipment in extreme low-temperature environments (-269 °C), almost demanding requirements are put forward for structural materials, and existing materials or stainless steels cannot meet the requirements of ultra-high strength (yield strength ≥ 1500 MPa, tensile strength ≥ 1900 MPa), high toughness, and non-magnetic properties.

[0037] Therefore, the present invention provides a high-strength, tough, and non-magnetic stainless steel sheet. By weight percentage, its chemical composition is: C ≤ 0.006%, N: 0.35 - 0.45%, O ≤ 0.0020%, P ≤ 0.010%, S ≤ 0.005%, Cr: 21.0 - 22.0%, Ni: 15.0 - 16.5%, Mo: 2.3 - 2.6%, Mn: 6.2 - 10.0%, Si ≤ 0.20%, Nb < 0.04%, V: 0.15 - 0.25%, Cu: 0.10 - 0.15%, Al ≤ 0.02%, Ti ≤ 0.02%, Co ≤ 0.05%, and the balance is Fe and unavoidable impurities.

[0038] Compared with the prior art, in the present invention, through the design of alloy components, the C content is controlled to be less than 0.006% and the oxygen content is less than 0.002%; the N content is precisely controlled at 0.35 - 0.45%; at the same time, the Mn content needs to be strictly controlled at 6.2 - 10.0%, the Nb content is less than 0.04%, and the Mo content is 2.3 - 2.6%; the contents of Ti and Al elements are restricted. Through the interaction between elements, solid-solution strengthening and grain refinement are achieved, and at the same time, the contents of niobium nitride, titanium nitride, and aluminum nitride in the stainless steel at high temperatures are significantly reduced, ensuring the strength and toughness of the stainless steel sheet. At the ultra-low temperature of -269 °C liquid helium temperature, the yield strength of the stainless steel sheet is above 1500 MPa, the tensile strength is above 1900 MPa, the elongation after fracture is above 30%, the V-notch impact energy is 150 - 170 J, and the fracture toughness is 160 - 200 MPa·m 1 / 2 , and the relative magnetic permeability < 1.01.

[0039] The functions of each element in the present invention are as follows:

[0040] Carbon: C is an austenite stabilizing element, and according to the Ni eq formula, its austenite stabilizing effect is more effective than that of Ni. However, the presence of the C element is likely to precipitate carbides Cr at the grain boundaries 23C6 causes the matrix near the austenite grain boundary to be depleted of Cr, thus greatly reducing its intergranular corrosion resistance. To avoid the precipitation of M 23 C6 carbides and maintain the C content in the steel, a combination of C and N can be used. Therefore, an ultra-low carbon content needs to be controlled in the steel of the present invention. Considering comprehensively, the carbon in the steel of the present invention is controlled within 0.006%.

[0041] Nitrogen: Nitrogen is an interstitial alloying element dissolved in the austenite lattice and can play a role in solid solution strengthening. According to the Ni eq formula, N is a stronger austenite-forming element and austenite stabilizer than Ni. In Cr-Ni steels, N reduces the content of δ-ferrite. Therefore, in the present invention, the nitrogen content range is precisely controlled to be 0.35 - 0.45%.

[0042] Chromium: Chromium is a ferrite-stabilizing element. Increasing the chromium content promotes the formation of high-temperature Cr2N and medium-temperature M 23 C6, thus seriously deteriorating the hot workability and low-temperature toughness of the steel. In addition, chromium passivates the steel. Therefore, an increase in the chromium content improves the corrosion resistance of the steel. The addition of Cr improves the oxidation resistance of the alloy at higher temperatures. Compared with interstitial alloying elements, Cr also has a medium solid solution strengthening effect. The addition of Cr can increase the yield strength and tensile strength of the steel. Therefore, the chromium content range of the steel of the present invention is 21.0 - 22.0%.

[0043] Nickel: Nickel is an alloying element that stabilizes austenite. At the same time, it can inhibit the formation of high-temperature δ-ferrite. Adding more and more nickel to 18% Cr ferritic stainless steel, the structure gradually transforms into austenite. There is a certain relationship between the Ni and Cr contents required to maintain the austenite structure. At the 18% Cr level, if the %Ni is about 8%, the austenite structure persists at room temperature. When the Cr content is higher or lower, the Ni content must be adjusted to maintain a fully austenite structure, and vice versa. In addition, nickel can improve the low-temperature properties of nickel-chromium-based austenitic stainless steels. Considering comprehensively, the nickel content range of the steel of the present invention is 15.0 - 16.5%.

[0044] Molybdenum: Molybdenum is an alloying element that forms ferrite. After adding Mo, the hardness of the alloy increases, but the effect of Mo is less than that of C and N. Mo introduces lattice strain, increasing the tensile strength and yield strength of the alloy. The addition of Mo can also improve the thermal strength of the alloy and reduce its hot plasticity. Mo also promotes the formation of intermetallic phases, especially the sigma phase that causes embrittlement at room temperature. To minimize the ferrite content in the as-cast (austenite) product at room temperature, the composition balance must be carefully controlled during steelmaking. Considering comprehensively, the molybdenum content of the steel of the present invention is 2.3 - 2.6%.

[0045] Manganese: As the core alloying element of high-nitrogen austenitic stainless steel, manganese realizes the efficient solid solution of nitrogen and structural stability through a dual mechanism: First, its unique electron layer structure can form a strong binding force with nitrogen atoms, significantly increasing the solubility of nitrogen in the austenite matrix during high-temperature melting, making it a key carrier for the design of high-nitrogen steel; at the same time, as a strong austenite-forming element, by expanding the range of the γ-phase region, the high-nitrogen austenite structure remains metastable at room temperature, effectively suppressing high-temperature δ-ferrite, thereby reducing the magnetic permeability.

[0046] In terms of process, the addition of manganese reduces the critical cooling rate to the operable range of conventional quenching, ensuring that thick-section components obtain a fully austenitic structure, and its substitution effect for nickel significantly reduces the material cost while maintaining phase stability. Based on the above synergistic effects, to achieve the best balance between the high-nitrogen solid solution strengthening effect and processing performance, the manganese content of the steel in this invention is 6.2 - 10.0%.

[0047] Silicon: Si is a ferrite-forming element, and it can improve the corrosion resistance of steel, while playing a deoxidizing role during alloy smelting. The Si element generally reduces the mechanical properties of the alloy and increases the tendency of welding hot cracking. Excessive addition of the Si element will increase the precipitation probability of ferrite in the alloy and trigger the precipitation of chromium carbide at the grain boundaries, depleting the Cr element at the grain boundaries and deteriorating the mechanical and corrosion resistance of the alloy. Therefore, it needs to be strictly controlled. Considering the above, the silicon in the steel of this invention is controlled within 0.2%.

[0048] Phosphorus and sulfur: P and S are impurity elements in steel. P can significantly reduce the corrosion resistance of chromium-nickel stainless steel in the solid solution state and sensitized state to nitric acid corrosion at various concentrations. S can reduce the hot plasticity of stainless steel, affect the hot workability of steel, and S will also reduce the corrosion resistance of stainless steel. Since the steel in this invention adopts a double ultra-pure smelting process of low-cost electric furnace + electroslag remelting and selects pure metal materials for smelting, the phosphorus and sulfur contents are respectively controlled within 0.010% and 0.005%.

[0049] Oxygen: O is a harmful element in steel. The O element 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 steel of this invention is controlled within 0.0020% (20 ppm).

[0050] Vanadium: A small amount of V can play a role in refining grains and improving the strength and toughness of steel. However, excessive V will form V(C, N) with C and N, reducing the low-temperature toughness of steel. Considering the above, the vanadium content in the steel of this invention is 0.15 - 0.25%.

[0051] Niobium: Adding Nb to stainless steel can prevent intergranular corrosion. Nb can refine grains, reduce the overheating sensitivity and temper brittleness of steel, and improve strength, but the plasticity and toughness decrease to some extent. Considering comprehensively, the niobium content in the steel of this invention is controlled < 0.04%.

[0052] Copper: Copper is a common alloying element in stainless steel and has a wide range of uses. In austenitic stainless steel, the addition of copper can improve its strength and corrosion resistance, but at the same time, it will reduce its antioxidant ability. Therefore, the copper content in the steel of the present invention is 0.10 - 0.15%.

[0053] Aluminum: Al is a commonly used deoxidizer in steel. Adding a small amount of Al to steel can refine the grain size and improve the impact toughness. Aluminum also has antioxidant and corrosion resistance properties. When Al is used in combination with Cr and Si, it can significantly improve the scale resistance and high-temperature corrosion resistance of steel. However, Al will form high-temperature AlN, which will damage the plasticity and toughness and hot working performance of the steel. Therefore, the aluminum content in the steel of the present invention must be strictly controlled within 0.02%.

[0054] Titanium: The addition of Ti can refine the austenite grain size and indirectly improve the strength and toughness of the material. However, excessive Ti will combine with N or C in the steel to form hard and brittle TiN or TiC inclusions. Therefore, the titanium content in the steel of the present invention must be strictly controlled within 0.02%.

[0055] Cobalt: As an austenite stabilizing element, Co dissolved in the matrix can improve the high-temperature strength and creep resistance of the material. In the nuclear industry, Co may be used to regulate the irradiation performance of the material, but attention should be paid to its activation problem. The addition of excessive Co may interfere with the 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 steel of the present invention must be strictly controlled within 0.05%.

[0056] Specifically, by weight percentage, its chemical composition is: C ≤ 0.006%, N: 0.37 - 0.45%, O ≤ 0.0020%, P ≤ 0.010%, S ≤ 0.005%, Cr: 21.0 - 21.5%, Ni: 15.0 - 15.4%, Mo: 2.3 - 2.5%, Mn: 7.0 - 10.0%, Si ≤ 0.20%, Nb < 0.04%, V: 0.15 - 0.19%, Cu: 0.10 - 0.15%, Al ≤ 0.02%, Ti: 0.012 - 0.02%, Co ≤ 0.04%, and the balance is Fe and unavoidable impurities.

[0057] The present invention provides a method for manufacturing a high-strength, tough and non-magnetic stainless steel sheet, comprising the following steps:

[0058] S1: Weigh the materials according to the alloy composition, and obtain an electroslag ingot after electric furnace smelting and electroslag remelting;

[0059] S2: Subject the electroslag ingot to high-temperature diffusion, and then perform forging to obtain a forging billet;

[0060] S3: Roll the obtained forging billet to obtain a rolled sheet;

[0061] S4: Finally, the obtained rolled sheet is subjected to solution treatment to obtain a high-strength, tough and non-magnetic stainless steel sheet.

[0062] Compared with the prior art, based on the compounding of alloy components, the present invention provides a preparation method of a stainless steel sheet, mainly through processes such as melting, forging, rolling and heat treatment in an electric furnace and electroslag remelting. On the one hand, it can reduce production costs, use an electric furnace instead of an intermediate frequency induction furnace without affecting the performance of the final stainless steel sheet; on the other hand, based on the coordinated regulation of composition-method-structure, through technical means such as high-nitrogen interstitial solid solution strengthening, fine grain strengthening and carbon / nitride precipitation strengthening, the yield strength of the steel of the present invention is higher than 1500 MPa at -269 °C, and at the same time, the grain structure is uniform, the grains are refined, and it can reach 4-7 grades.

[0063] Specifically, in step S1, after electric furnace smelting, AOD and LF smelting are carried out; the casting temperature is 1480 - 1520 °C.

[0064] Specifically, in step S1, during electroslag remelting, the slag system is a ternary slag system of CaF2 - Al2O3 - CaO, and remelting is carried out under an argon protection atmosphere. After remelting is completed, the ingot is removed after >1 h.

[0065] It should be noted that the present invention uses a 40t electric furnace + AOD + LF smelting. During the AOD refining process, oxygen is blown and argon is used for decarburization, and then nitrogen is blown to increase nitrogen. During the LF refining stage, Al is used for deoxidation and the alloy is finely adjusted to ensure that each element reaches the target composition.

[0066] The preferred process for electroslag remelting includes: using a die-cast electrode bar (i.e., the ingot obtained after electric furnace + AOD + LF smelting) as the consumable electrode for electroslag remelting, the slag system is a ternary slag system of CaF2 - Al2O3 - CaO, and remelting is carried out under an argon protection atmosphere. After remelting is completed, the ingot is removed after >1 h.

[0067] In the present invention, the weight ratio of CaF2, Al2O3, and CaO in the ternary slag system of CaF2 - Al2O3 - CaO is 70:15:15.

[0068] Specifically, the temperature of the high-temperature diffusion is 1190 - 1210 °C. During the forging process, the starting forging temperature is ≥1050 °C, and the final forging temperature is ≥900 °C.

[0069] Specifically, the forging ratio is greater than 6.

[0070] It should be noted that in the present invention, the Cr element and the N element will form a Cr2N brittle phase. Before forging, high-temperature diffusion is carried out at 1190 - 1210 °C to completely dissolve the Cr2N brittle phase. High-temperature diffusion in this temperature range also makes the diffusion of the Nb element more uniform, thereby ensuring the strength, toughness, etc. of the final stainless steel sheet.

[0071] In the present invention, the temperature of high-temperature diffusion can be 1190 °C, 1195 °C, 1200 °C, 1205 °C or 1210 °C.

[0072] In the present invention, during the forging process, a forging method of upsetting and drawing is adopted, and the forging ratio is controlled to be greater than 6, deforming from an electroslag ingot with a φ770 specification to a forging blank with a thickness of δ100 - 180 mm.

[0073] Specifically, during the rolling process, the pre-rolling heat preservation temperature is 1160 - 1180 °C, the starting rolling temperature ≥ 1050 °C, and the finishing rolling temperature ≥ 900 °C.

[0074] Specifically, the rolling ratio is not less than 2.

[0075] It should be noted that in the present invention, the pre-rolling heat preservation temperature is controlled at 1160 - 1180 °C, and at the same time, the rolling ratio is controlled to be not less than 2. Deforming from a forging blank with a thickness of δ100 - 180 mm to a sheet with a thickness of δ4 - 90 mm can control the grain size and avoid excessive coarsening of grains. Appropriate rolling temperature helps the diffusion of alloying elements, thereby obtaining a more uniform structure. The pre-rolling heat preservation temperature in the present invention can be 1160 °C, 1167 °C, 1170 °C, 1175 °C or 1180 °C.

[0076] Specifically, the heat preservation temperature of the solution treatment is 1000 - 1100 °C, the heat preservation time is 30 - 150 min, and after the solution treatment, it is rapidly cooled to room temperature by water quenching.

[0077] It should be noted that in the present invention, after rolling, solution treatment is required, and the solution temperature is controlled at 1000 - 1100 °C, which can be 1000 °C, 1010 °C, 1020 °C, 1030 °C, 1030 °C, 1050 °C, 1060 °C, 1070 °C, 1080 °C, 1090 °C or 1100 °C, preferably 1050 - 1070 °C.

[0078] In the present invention, when the solution temperature exceeds 1100 °C, the grains grow abnormally and coarsen, reducing the strength and toughness of the stainless steel sheet; when the solution temperature is lower than 1000 °C, the precipitated phase cannot redissolve, which will also affect the performance of the stainless steel sheet.

[0079] Specifically, the stainless steel sheet provided by the present invention is used in the structural members of high-strength magnetic field superconducting magnets, deep space exploration and ultra-low temperature devices at -296 °C liquid helium temperature.

[0080] It should be noted that the stainless steel sheet produced by the present invention has high strength and toughness. At the ultra-low temperature of -269°C liquid helium temperature, the yield strength of the stainless steel sheet is above 1500 MPa, the tensile strength is above 1900 MPa, the elongation after fracture is above 30%, the V-notch impact energy is 150 - 170 J, and the fracture toughness is 160 - 200 MPa·m 1 / 2 , and the relative magnetic permeability < 1.01, and it can fully withstand the use at the liquid helium temperature of -296°C. Therefore, it can be used in the structural components of high magnetic field superconducting magnets, deep space exploration, and ultra-low temperature devices at the liquid helium temperature of -296°C.

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

[0082] Example 1

[0083] The manufacturing method of the stainless steel sheet includes the following steps:

[0084] S1: Weigh the materials according to the alloy composition, and obtain an electroslag ingot after electric furnace and electroslag remelting;

[0085] Among them, the smelting adopts a 40t electric furnace, AOD and LF smelting,

[0086] Among them, the slag system in electroslag remelting is CaF2 - Al2O3 - CaO = 70%: 15%: 15%;

[0087] S2: Perform high-temperature diffusion on the φ770mm electroslag ingot, and then perform forging to obtain a forging blank of 150mm × 630mm × L, and the forging ratio is 8;

[0088] The temperature of the high-temperature diffusion is 1210°C. During the forging process, the starting forging temperature is 1110°C, and the final forging temperature is 940°C;

[0089] S3: Roll the obtained forging blank to obtain a rolled sheet with a thickness of δ75mm × a width of 630mm × L, and the rolling ratio is 2;

[0090] During the rolling process, the holding temperature of the forging blank before rolling is 1170°C, the starting rolling temperature is 1060°C, and the final rolling temperature is 900°C;

[0091] S4: Finally, perform solution treatment on the obtained rolled blank. The holding temperature of the solution treatment is 1050°C, the holding time is 120 min, and after the solution treatment, it is rapidly cooled to room temperature by water quenching to obtain a high-strength and tough non-magnetic stainless steel sheet.

[0092] The chemical composition of the sheet in this example is shown in Table 1.

[0093] Examples 2 - 5

[0094] Examples 2-5 are generally the same as Example 1 in terms of ingredients and preparation process, with the differences shown in Table 1 and Table 2.

[0095]

[0096]

[0097] Comparative Example 1

[0098] Comparative Example 1 adopts the preparation method and ingredient ratio of Example 1 in the invention patent with publication number CN117286426A. Specifically as follows:

[0099] Chemical composition: C: 0.0058%, N: 0.27%, O: 0.0013%, P: 0.0046%, S: 0.0036%, Cr: 21.67%, Ni: 14.47%, Mo: 1.92%, Mn: 6.0%, Si: 0.13%, Nb: 0.07%, V: 0.13%, Cu: 0.15%, Al: 0.008%, H: 0.00057%;

[0100] Preparation method:

[0101] Smelting: Medium-frequency induction furnace and electroslag remelting, and the slag system for electroslag remelting is the quaternary slag system of CaF2 - Al2O3 - CaO - MgO;

[0102] Forging: High-temperature diffusion is carried out before forging, and the temperature is 1210°C; the blooming forging temperature is 1070°C; the final forging temperature is 890°C;

[0103] Heat treatment process: The solution temperature is 1120°C, and the holding time is 2h.

[0104] Comparative Example 2

[0105] Comparative Example 2 is generally the same as Example 1 in the preparation process, except that the material used in Comparative Example 2 is 316LN.

[0106] Comparative Example 3

[0107] Comparative Example 3 is generally the same as Example 1 in the preparation process, except that in Comparative Example 3, the N content is 0.27% and the Mn content is 5.5%.

[0108] Comparative Example 4

[0109] Comparative Example 4 is generally the same as Example 1 in the preparation process, except that in Comparative Example 4, the Ti content is 0.05% and the Co content is 0.08%.

[0110] Comparative Example 5

[0111] The preparation process of Comparative Example 5 is substantially the same as that of Example 1, except that the solution temperature in Comparative Example 5 is 1170°C.

[0112] Performance Testing

[0113] The above-mentioned Examples 1-5 and Comparative Examples 1-5 were subjected to performance tests, mainly including yield strength, tensile strength, impact toughness, elongation after fracture, and fracture toughness. The test temperature was -269°C, and the test results are shown in Table 3.

[0114]

[0115] Combined with Examples 1-5 and Comparative Examples 1-5 and referring to Figures 1 to 9 It can be seen that by using the composition ratio and manufacturing method of Examples 1-5 of the present invention, the yield strength of the obtained stainless steel plate is 1514-1693MPa, the tensile strength is 1920-1983MPa, the elongation after fracture is 33-40%, the V-type impact energy is 153~169J, and the fracture toughness K IC 162-193MPa·m 1 / 2 , and the relative magnetic permeability is less than 1.01.

[0116] In addition, by observing the microstructure diagram and the fracture microscopic characterization diagram, it can be seen that the grain size of the steel plate of the present invention is uniform, the size distribution is uniform, and the grain size can reach 4-7 levels. The microstructure is an austenite matrix without M 23 C6 carbide and δ-ferrite. A large number of dimples are found in the cross-section after the tensile test at -269℃, indicating that the invented steels all have ductile fracture.

[0117] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A high-strength, tough and non-magnetic stainless steel sheet, characterized in that, By weight percentage, its chemical composition is: C ≤ 0.006%, N: 0.35 - 0.45%, O ≤ 0.0020%, P ≤ 0.010%, S ≤ 0.005%, Cr: 21.0 - 22.0%, Ni: 15.0 - 16.5%, Mo: 2.3 - 2.6%, Mn: 6.2 - 10.0%, Si ≤ 0.20%, Nb < 0.04%, V: 0.15 - 0.25%, Cu: 0.10 - 0.15%, Al ≤ 0.02%, Ti ≤ 0.02%, Co ≤ 0.05%, and the balance is Fe and unavoidable impurities; At the ultra-low temperature of -269°C (liquid helium temperature), the yield strength of the stainless steel sheet is above 1500 MPa, and the tensile strength is above 1920 MPa; the V-notch impact energy is 150 - 170 J, and the fracture toughness is 160 - 200 MPa·m 1 / 2 ; the grain size grade of the stainless steel sheet is 4 - 7; there is no M 23 C6 type carbide and δ-ferrite.

2. The high-strength, tough and non-magnetic stainless steel sheet according to claim 1, wherein By weight percentage, its chemical composition is: C ≤ 0.006%, N: 0.37 - 0.45%, O ≤ 0.0020%, P ≤ 0.010%, S ≤ 0.005%, Cr: 21.0 - 21.5%, Ni: 15.0 - 15.4%, Mo: 2.3 - 2.5%, Mn: 7.0 - 10.0%, Si ≤ 0.20%, Nb < 0.04%, V: 0.15 - 0.19%, Cu: 0.10 - 0.15%, Al ≤ 0.02%, Ti: 0.012 - 0.02%, Co ≤ 0.04%, and the balance is Fe and unavoidable impurities.

3. The high-strength, tough and non-magnetic stainless steel sheet according to claim 1, wherein, At the ultra-low temperature of -269°C (liquid helium temperature), the yield strength of the stainless steel sheet is above 1500 MPa, the tensile strength is above 1900 MPa, the elongation after fracture is above 30%, the V-notch impact energy is 150 - 170 J, and the fracture toughness is 160 - 200 MPa·m 1 / 2 , and the relative permeability < 1.

01.

4. A manufacturing method of the high-strength, tough and non-magnetic stainless steel sheet according to any one of claims 1-3, characterized in that, It includes the following steps: S1: Charge materials according to the alloy composition, and obtain an electroslag ingot after electric furnace smelting and electroslag remelting; S2: Perform high-temperature diffusion on the electroslag ingot, and then forge it to obtain a forged billet; S3: Roll the obtained forged billet to obtain a rolled sheet; S4: Finally, perform solution treatment on the obtained rolled sheet to obtain a high-strength, tough and non-magnetic stainless steel sheet.

5. The manufacturing method of the high-strength and tough non-magnetic stainless steel sheet according to claim 4, characterized in that, Perform AOD and LF smelting after electric furnace smelting; the steel casting temperature is 1480 - 1520 °C.

6. The manufacturing method of the high-strength and tough non-magnetic stainless steel sheet according to claim 4, characterized in that, During electroslag remelting, the slag system is a ternary slag system of CaF2 - Al2O3 - CaO, and it is remelted under an argon protection atmosphere. The ingot is removed more than 1 h after the remelting ends.

7. The manufacturing method of the high-strength and tough non-magnetic stainless steel sheet according to claim 4, characterized in that, The temperature of the high-temperature diffusion is 1190 - 1210 °C. During the forging process, the starting forging temperature ≥ 1050 °C, and the final forging temperature ≥ 900 °C.

8. The manufacturing method of the high-strength and tough non-magnetic stainless steel sheet according to claim 4, characterized in that, During the rolling process, the pre-rolling holding temperature is 1160 - 1180 °C, the starting rolling temperature ≥ 1050 °C, and the final rolling temperature ≥ 900 °C.

9. The manufacturing method of the high-strength and tough non-magnetic stainless steel sheet according to claim 4, characterized in that, The holding temperature of the solution treatment is 1000 - 1100 °C, the holding time is 30 - 150 min, and after the solution treatment, it is rapidly cooled to room temperature by water quenching.

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