Hierarchical construction method for nanophase in steel and high-toughness and ultrahigh-strength steel prepared through hierarchical construction method at low cost

Abstract

The invention provides a hierarchical construction method for nanophase in steel and high-toughness and ultrahigh-strength steel prepared through the hierarchical construction method at low cost, and belongs to the technical field of high-toughness and ultrahigh-strength steel metallurgy. By optimizing the proportion of chemical components, adding filaments such as Al, Ti and composite rare earth during smelting and adjusting a heat treatment process, a nanophase is constructed in the steel step by step, in different temperature zones and in different levels, so that the strength, plasticity / toughness and the like of the steel are improved, and the service requirement of an extreme environment is met. The tensile strength Rm of the high-toughness ultrahigh-strength steel is larger than or equal to 2000 MPa, and the impact energy Aku of the high-toughness ultrahigh-strength steel is larger than or equal to 70 J. The preparation method is high in operability and controllable in component, compared with a traditional smelting and deoxidation process, the hierarchical construction of the nanophase is beneficial for improving the strength and the plasticity / toughness of the alloy at the same time, the production cost is reduced, and the preparation method can be industrially popularized and applied.

Description

Technical Field

[0001] The present invention relates to the technical field of high toughness and ultra-high strength steel metallurgy, and in particular to a method for constructing a nano-phase hierarchy in steel and a high toughness and ultra-high strength steel obtained at low cost. Background Art

[0002] With the continuous optimization and upgrading of the performance of strategic equipment systems such as modern military equipment, aircraft and spacecraft, and shipborne vehicles, metallic materials face more stringent technical requirements in key service indicators such as strength limit, fracture toughness, and creep resistance. Especially under extreme service conditions, the performance stability faces major challenges. As an important part of the advanced structural material system, ultra-high strength and toughness steel shows significant advantages in core mechanical parameters such as ultimate tensile strength, dynamic impact toughness, and elastic modulus. It has been widely used not only in high-speed rail transit equipment, heavy machinery equipment, and major civil infrastructure fields, but also gradually extended to high-end equipment manufacturing in the field of national defense science and technology and other cutting-edge application scenarios with special requirements for material performance. In typical ultra-high strength and toughness steel varieties such as aircraft landing gear special steel, precision bearing steel, steel for high-pressure hydraulic system piston pumps, and steel for aerospace propulsion system engines, there are still significant technical bottlenecks at the industrial preparation technology level. Specifically, it is manifested as: obvious coarsening trend of the material microstructure, insufficient control level of internal defects (such as non-metallic inclusions, micro-cracks), imperfect strength-toughness collaborative optimization mechanism, etc. These technical defects at the material level directly lead to a decrease in the service reliability of key components, and there is an obvious performance gap compared with the international advanced level, which has seriously restricted the overall performance and service life of major technical equipment.

[0003] The secondary hardening type ultra-high strength steel, with its high cobalt and nickel alloying design and extraordinary strength characteristics (tensile strength can reach 1960 MPa), has become the core material for aircraft landing gears and key load-bearing components in national defense. However, its high production cost limits its widespread application. Since the system evolution in the 1960s (9Ni-4Co→HY180→AF1410→AerMet100→AerMet310→AerMet340), through precise regulation of alloying elements and improvement of metallurgical purity, this steel type has achieved the synergistic optimization of strength and toughness. Among them, the AerMet series developed in the past two decades (such as the ultimate tensile strength of AerMet100 is 1930 MPa and the fracture toughness is 100 ksi) has gradually replaced traditional steel types. The strengthening mechanism of the secondary hardening type ultra-high strength steel stems from the synergistic effect of the coherent precipitation of alloy carbides (mainly of the M2C type) during high-temperature tempering and the secondary quenching transformation of retained austenite. However, when the secondary hardening reaches its maximum, the toughness of the steel is poor, and the toughness of the steel can be significantly improved through over-aging, but this will lead to a significant reduction in the strength of the steel. Current research focuses on breaking through the strength-toughness limit through the synergistic regulation of reasonable chemical composition ratios (such as the addition of Co promotes the increase in the nucleation density of carbides (Co content up to 15%), and Cr partially replaces Mo to reduce the lattice constant of M2C to enhance the interface coherency) and adjustment of heat treatment processes. In addition, due to the deterioration of the melt fluidity in the medium and high alloy system secondary hardening steel, it is easy to cause composition segregation, and there is a high risk of cracking in engineering applications. Therefore, the homogenization smelting process and improved heat treatment methods are the research hotspots and difficulties for medium and high alloy ultra-high strength steels.

[0004] Based on this, it is very important to provide a high-toughness ultra-high strength steel and its preparation method. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for constructing a nano-phase hierarchy in steel and a high-toughness ultra-high strength steel prepared at low cost, so as to solve the technical problem in the prior art that it is impossible to improve the strength of steel while improving its toughness.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a high-toughness ultra-high strength steel, and the chemical composition of the high-toughness ultra-high strength steel includes: C 0.20 - 0.25%, Si ≤ 0.02%, Mn ≤ 0.02%, Ni 8.5 - 10.5%, Cr 1.60 - 2.50%, Mo 0.9 - 1.3%, Al 0.015 - 0.025%, Co 6.5 - 8.5%, Nb 0.015 - 0.022%, Ti 0.015 - 0.02%, W ≤ 0.5%, composite rare earth elements ≤ 0.03%, P ≤ 0.01%, S ≤ 0.01%, and the balance is Fe;

[0008] The composite rare earth elements include La and Ce, and the mass ratio of La to Ce is 1:1.

[0009] The present invention provides a method for constructing a nano-phase hierarchy in the high-toughness ultra-high-strength steel as described above, comprising the following steps:

[0010] 1) Mix the raw materials corresponding to the chemical composition of the high-toughness ultra-high-strength steel and conduct vacuum melting to obtain molten steel;

[0011] 2) Feed composite filaments into the molten steel, and conduct refining and casting in sequence to obtain an ingot;

[0012] 3) Forge the ingot by using a three-forging and three-drawing forging process, and then conduct quenching, cryogenic treatment, first medium-temperature tempering, and second low-temperature tempering in sequence to obtain the high-toughness ultra-high-strength steel.

[0013] Furthermore, the vacuum degree of the vacuum melting is 1-5 Pa, and the power of the vacuum melting is 50-180 kW.

[0014] Furthermore, the composite filaments include Al filaments, Ti filaments, and composite rare earth filaments. The rare earth elements in the composite rare earth filaments are La and Ce, and the mass ratio of La to Ce is 1:1;

[0015] The diameter of the composite filaments is 0.5-1.5 mm;

[0016] The oxygen content of the composite rare earth filaments is less than 40 ppm.

[0017] Furthermore, the diameter of the Al filaments is 0.5-1.5 mm;

[0018] The diameter of the Ti filaments is 0.5-1.5 mm;

[0019] The diameter of the composite rare earth filaments is 0.5-1.5 mm.

[0020] Furthermore, the feeding speed of the composite filaments is 0.05-1.5 m / s;

[0021] The mass of the fed Al filaments is 0.015-0.5% of the total mass of the raw materials, the mass of the fed Ti filaments is 0.015-0.45% of the total mass of the raw materials, and the mass of the fed composite rare earth filaments is 0.000-0.035% of the total mass of the raw materials.

[0022] Furthermore, the power of the refining is 80-160 kW;

[0023] The vacuum degree of the casting is 1-5 Pa, and the power of the casting is 60-100 kW.

[0024] Furthermore, in the three-upsetting and three-drawing forging process, the initial forging temperature is 1050 - 1100 °C, the final forging temperature is ≥950 °C, and the forging ratio is ≥6.

[0025] Furthermore, the quenching temperature is 850 - 920 °C, and the quenching time is 1 - 2 h;

[0026] The cryogenic treatment temperature is -80 - -70 °C, and the cryogenic treatment time is 0.5 - 2 h.

[0027] Furthermore, the temperature of the first medium-temperature tempering is 460 - 520 °C, and the time of the first medium-temperature tempering is 4 - 6 h;

[0028] The temperature of the second low-temperature tempering is 220 - 250 °C, and the time of the second low-temperature tempering is 1 - 3 h.

[0029] Advantages of the present invention:

[0030] During the smelting of the present invention, Al filaments, Ti filaments, composite rare earth filaments are added and the heat treatment process is adjusted to hierarchically construct multiple nano-phases in the high-toughness ultra-high-strength steel (Rm≥2000 MPa); through reasonable process control, oxidation reaction occurs in the molten steel, and by strengthening the stirring of the melt, the interfacial concentration gradient of nano-particles in the molten steel is controlled to form nano-scale oxides. This type of nano-oxide can serve as heterogeneous nucleation to refine the microstructure, with the grain size ≥ grade 10. At the same time, it can also serve as the nucleation core of metal carbides, improve its nucleation rate, refine the carbides (replacing the precious metal Co element), and prevent them from precipitating at the grain boundaries and weakening the grain boundaries, achieving the purpose of hierarchically constructing nano-phases in the steel in a "step-by-step temperature zone", thereby improving its strength, plasticity / toughness, etc., and meeting the service requirements in extreme environments. In particular, the content of Co in the steel is reduced, and the production cost is lowered;

[0031] The preparation method of the present invention has strong operability and controllable composition. Compared with the traditional melting and deoxidation processes, the oxides formed in the melt of the high-toughness ultra-high-strength steel (Rm≥2000 MPa) of the present invention are fine, and can also achieve the effect of heterogeneous nucleation. Hierarchically constructing multiple nano-phases is beneficial to improving and stabilizing the strength and toughness of the high-toughness ultra-high-strength steel (Rm≥2000 MPa), with low cost, and can be industrially promoted and applied. Description of the Drawings

[0032] Figure 1 It is a physical diagram of the Ti filament in Embodiment 1 of the present invention;

[0033] Figure 2 It is a microstructural diagram of the high-toughness ultra-high-strength steel prepared in Embodiment 1 of the present invention;

[0034] Figure 3It is the tensile stress-strain curve of the high-toughness ultra-high strength steel prepared in Example 1 of the present invention. Detailed implementation mode

[0035] The present invention provides a high-toughness ultra-high strength steel, and the chemical composition of the high-toughness ultra-high strength steel includes: C 0.20-0.25%, Si ≤ 0.02%, Mn ≤ 0.02%, Ni 8.5-10.5%, Cr 1.60-2.50%, Mo 0.9-1.3%, Al 0.015-0.025%, Co 6.5-8.5%, Nb 0.015-0.022%, Ti 0.015-0.02%, W ≤ 0.5%, composite rare earth elements ≤ 0.03%, P ≤ 0.01%, S ≤ 0.01%, and the balance is Fe;

[0036] The composite rare earth elements include La and Ce, and the mass ratio of La and Ce is 1:1.

[0037] In the present invention, by hierarchically constructing multiple nano-phases in the steel, both strength and toughness are increased. At the same time, considering the high cost brought by the high Co element content in traditional secondary hardening ultra-high strength steels, through a reasonable chemical composition ratio, multiple nano-phases are hierarchically constructed in the steel, reducing the Co content in the steel and saving production costs, and its popularization and application have important significance.

[0038] The present invention provides a method for hierarchically constructing nano-phases in the above-mentioned high-toughness ultra-high strength steel, including the following steps:

[0039] 1) Mix the raw materials corresponding to the chemical composition of the high-toughness ultra-high strength steel, and conduct vacuum melting to obtain molten steel;

[0040] 2) Feed composite filaments into the molten steel, and conduct refining and casting in sequence to obtain an ingot;

[0041] 3) Forge the ingot by using a three-forging and three-drawing forging process, and then conduct quenching, cryogenic treatment, first medium-temperature tempering, and second low-temperature tempering in sequence to obtain the high-toughness ultra-high strength steel.

[0042] In the present invention, the vacuum degree of the vacuum melting is 1-5 Pa, preferably 2-4 Pa, and more preferably 3 Pa; the power of the vacuum melting is 50-180 kW, preferably 60-170 kW, and more preferably 70-160 kW.

[0043] In the present invention, the composite filaments include Al filaments, Ti filaments and composite rare earth filaments, and the rare earth elements in the composite rare earth filaments are La and Ce, and the mass ratio of La and Ce is 1:1.

[0044] In the present invention, the diameter of the composite filament is 0.5 to 1.5 mm, preferably 0.6 to 1.3 mm, and more preferably 0.8 to 1 mm;

[0045] The oxygen content of the composite rare earth filament is less than 40 ppm, preferably less than 35 ppm, and more preferably less than 30 ppm.

[0046] In the present invention, the purpose of the oxygen content of the composite rare earth filament being less than 40 ppm is to prevent the molten steel from increasing in oxygen.

[0047] In the present invention, the diameter of the Al filament is 0.5 to 1.5 mm, preferably 0.6 to 1.3 mm, and more preferably 0.8 to 1 mm; the diameter of the Ti filament is 0.5 to 1.5 mm, preferably 0.6 to 1.3 mm, and more preferably 0.8 to 1 mm; the diameter of the composite rare earth filament is 0.5 to 1.5 mm, preferably 0.6 to 1.3 mm, and more preferably 0.8 to 1 mm.

[0048] In the present invention, the feeding speed of the composite filament is 0.05 to 1.5 m / s, preferably 0.08 to 1.3 m / s, and more preferably 0.1 to 1 m / s;

[0049] The mass of the fed Al filament is 0.015 to 0.5% of the total mass of the raw materials, preferably 0.02 to 0.45%, and more preferably 0.025 to 0.4%; the mass of the fed Ti filament is 0.015 to 0.45% of the total mass of the raw materials, preferably 0.02 to 0.4%, and more preferably 0.025 to 0.35%; the mass of the fed composite rare earth filament is 0.000 to 0.035% of the total mass of the raw materials, preferably 0.005 to 0.03%, and more preferably 0.01 to 0.025%.

[0050] In the present invention, the purpose of feeding the composite filament into the molten steel is to control trace elements and react with oxygen to form particulate nano-oxides.

[0051] In the present invention, the power of the refining is 80 to 160 kW, preferably 90 to 150 kW, and more preferably 100 to 140 kW.

[0052] In the present invention, the vacuum degree of the casting is 1 to 5 Pa, preferably 2 to 4 Pa, and more preferably 3 Pa; the power of the casting is 60 to 100 kW, preferably 65 to 95 kW, and more preferably 70 to 90 kW.

[0053] In the present invention, in the three-upsetting and three-drawing forging process, the initial forging temperature is 1050 - 1100 °C, preferably 1050 - 1080 °C, and more preferably 1050 - 1070 °C; the final forging temperature is ≥ 950 °C, preferably 950 - 1000 °C, and more preferably 960 - 980 °C; the forging ratio is ≥ 6, preferably 6 - 9, and more preferably 7 - 8.

[0054] In the present invention, the quenching temperature is 850 - 920 °C, preferably 870 - 910 °C, and more preferably 880 - 900 °C; the quenching time is 1 - 2 h, preferably 1.2 - 1.8 h, and more preferably 1.4 - 1.6 h.

[0055] In the present invention, the cryogenic treatment temperature is - 80 - - 70 °C, preferably - 78 - - 72 °C, and more preferably - 76 - - 74 °C; the cryogenic treatment time is 0.5 - 2 h, preferably 0.7 - 1.8 h, and more preferably 1 - 1.5 h.

[0056] In the present invention, the temperature of the first intermediate temperature tempering is 460 - 520 °C, preferably 470 - 510 °C, and more preferably 480 - 500 °C; the time of the first intermediate temperature tempering is 4 - 6 h, preferably 4.5 - 5.5 h, and more preferably 5 h.

[0057] In the present invention, the temperature of the second low temperature tempering is 220 - 250 °C, preferably 225 - 245 °C, and more preferably 230 - 240 °C; the time of the second low temperature tempering is 1 - 3 h, preferably 1.5 - 2.5 h, and more preferably 2 h.

[0058] In the present invention, the quenching + cryogenic treatment + first intermediate temperature tempering + second low temperature tempering process is used to regulate multiple types of microstructures in the high-strength and tough steel, and the matrix microstructure is mainly tempered martensite.

[0059] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0060] Example 1

[0061] Accurately weigh 200 kg per furnace. The chemical composition of the high-toughness ultra-high-strength steel is: C 0.23%, Si 0.01%, Mn 0.01%, Ni 9.2%, Cr 2.1%, Mo 1.1%, Al 0.02%, Co 7.6%, Nb 0.018%, Ti 0.018%, W 0.3%, composite rare earth elements 0.025%, P 0.002%, S 0.002%, with the balance being Fe;

[0062] The composite rare earth elements include La and Ce, and the mass ratio of La to Ce is 1:1.

[0063] Charge the raw materials corresponding to the chemical composition of the high-toughness ultra-high-strength steel with large pieces close to the inner wall of the crucible and small pieces close to the center of the crucible. Close the furnace lid, turn on the vacuum pump, and evacuate the melting furnace to a vacuum degree of 3.0 Pa for vacuum melting. The temperature of the vacuum melting is 1600 °C. The process of vacuum melting is as follows: Set the power of the melting furnace to 90 kW, supply power to increase the temperature. When the metal in the crucible starts to melt, increase the power to 160 kW for melting. When melting causes splashing, reduce the power to 70 kW, turn off the vacuum pump, and at the same time fill the furnace with argon gas to increase the vacuum pressure value of the furnace body to 200 Pa. After completion, molten steel is obtained.

[0064] Feed Al filaments with a diameter of 0.8 mm and a length of 36.8 m, Ti filaments with a diameter of 0.8 mm and a length of 19.9 m, and composite rare earth filaments with a diameter of 0.8 mm and a length of 18.0 m into the molten steel at a speed of 0.9 m / s for deoxidation until the oxygen content ≤ 10 ppm. After melting is complete, take samples to detect the content of each element in the molten steel. Turn on the vacuum pump, set the refining power to 80 kW. After observing through the observation hole that the metal raw materials in the crucible are melted, continue refining until the molten steel starts to splash, cut off the power to cool down, and strengthen the stirring of the melt to promote the oxidation-reduction reaction of the molten steel. Lift the ingot mold and the launder, turn on the vacuum pump, evacuate to within 3 Pa, then supply power at 70 kW, and let it stand for 20 minutes before pouring to promote the floating of oxidation inclusions and improve the purity of the high-toughness ultra-high-strength steel. Then the operator tilts the crucible for pouring. After pouring, cool down, then open the air release valve to break the vacuum, open the furnace door, take out and disassemble the ingot mold to obtain a high-toughness ultra-high-strength steel ingot. Then perform a three-forging and three-drawing forging process (the initial forging temperature is 1060 °C, the final forging temperature is 965 °C, and the forging ratio is 8) to forge it into a bar. After forging, cool it in the furnace to prepare a steel bar with the required specifications and dimensions.

[0065] Quench the steel bar at 885 °C for 1 h, then perform cryogenic treatment at -73 °C for 1 h. After the cryogenic treatment, perform a first medium-temperature tempering at 470 °C for 5 h, and finally perform a second low-temperature tempering at 220 °C for 2 h. After completion, air-cool to room temperature to obtain a high-toughness ultra-high-strength steel. The matrix structure is mainly martensite tempered structure, and the grain size is 11.5 grades.

[0066] Example 2

[0067] Weigh accurately, 200 kg per furnace. The chemical composition of the high-toughness ultra-high-strength steel is as follows: C 0.22%, Si 0.01%, Mn 0.01%, Ni 8.5%, Cr 1.8%, Mo 1.2%, Al 0.02%, Co 7.2%, Nb 0.02%, Ti 0.019%, W 0.4%, composite rare earth elements 0.02%, P 0.003%, S 0.004%, with the balance being Fe;

[0068] The composite rare earth elements include La and Ce, and the mass ratio of La to Ce is 1:1.

[0069] Charge the raw materials corresponding to the chemical composition of the high-toughness ultra-high-strength steel in such a way that large pieces are close to the inner wall of the crucible and small pieces are close to the center of the crucible. Close the furnace lid, turn on the vacuum pump, and evacuate the melting furnace to a vacuum degree of 3.0 Pa for vacuum melting. The temperature of the vacuum melting is 1620 °C. The process of vacuum melting is as follows: Set the power of the melting furnace to 110 kW, supply power to raise the temperature. When the metal in the crucible starts to melt, increase the power to 150 kW for melting. When melting causes splashing, reduce the power to 60 kW, close the vacuum pump, and at the same time fill the furnace with argon gas to increase the vacuum pressure value of the furnace body to 250 Pa. After completion, molten steel is obtained;

[0070] Feed Al filaments with a diameter of 1 mm and a length of 23.6 m, Ti filaments with a diameter of 1 mm and a length of 13.5 m, and composite rare earth filaments with a diameter of 1 mm and a length of 9.3 m into the molten steel at a speed of 0.55 m / s for deoxidation until the oxygen content ≤ 10 ppm. After melting is complete, take samples to detect the content of each element in the molten steel; Turn on the vacuum pump, set the refining power to 100 kW. After observing through the observation hole that the metal raw materials in the crucible are melted, continue refining until the molten steel starts to splash, cut off the power to cool down, and strengthen the stirring of the melt to promote the oxidation-reduction reaction of the molten steel; Lift the ingot mold and the launder, turn on the vacuum pump, evacuate to within 3 Pa, then supply power of 100 kW, and let it stand for 10 minutes before pouring to promote the floating of oxidation inclusions and improve the purity of the high-toughness ultra-high-strength steel. Then the operator tilts the crucible for pouring; After pouring, cool down, then open the air release valve to break the vacuum, open the furnace door, take out and disassemble the ingot mold to obtain a high-toughness ultra-high-strength steel ingot, and then perform the three-forging and three-drawing forging process (the initial forging temperature is 1065 °C, the final forging temperature is 960 °C, and the forging ratio is 7) to forge it into a bar. After forging, it is cooled in the furnace to prepare a steel bar of the required specification size;

[0071] The steel bars are quenched at 890 °C for 1 h, then cryogenically treated at -73 °C for 1 h. After cryogenic treatment, a first medium-temperature tempering is carried out at 500 °C for 5 h, and finally a second low-temperature tempering is carried out at 230 °C for 2 h. After that, it is air-cooled to room temperature to obtain a high-toughness ultra-high-strength steel. The matrix structure is mainly tempered martensite, and the grain size is 11.0 grades.

[0072] Comparative Example 1

[0073] A high-toughness ultra-high-strength steel (Co content is 14.3%) is prepared according to the existing traditional means (electric furnace / converter smelting - refining - vacuum treatment - traditional continuous casting - electroslag - forging - heat treatment).

[0074] The mechanical properties and impact energy of the high-toughness ultra-high-strength steels prepared in Examples 1-2 and Comparative Example 1 are tested. The tensile method for mechanical property testing is carried out according to the GB / T 228.1-2010 standard; the impact energy is carried out according to the GB / T 229-2007 standard, and the test results are shown in Table 1.

[0075] Table 1 Performance test results of the high-toughness ultra-high-strength steels prepared in Examples 1-2 and Comparative Example 1

[0076]

[0077] It can be seen from the data in Table 1 that the Rm of the high-toughness ultra-high-strength steels prepared in Examples 1-2 are all higher than 2000 MPa, and the mechanical properties and impact energy are significantly higher than those of Comparative Example 1. The high-toughness ultra-high-strength steel samples prepared in the examples of the present invention are detected by special equipment for high-toughness ultra-high-strength steel. The mechanical properties of the prepared high-toughness ultra-high-strength steel materials and the impact energy of the high-toughness ultra-high-strength steel are significantly higher than those of Comparative Example 1. At the same time, the Co content is significantly reduced. Thus, it can be shown that this method can significantly improve the mechanical properties and impact energy of the high-toughness ultra-high-strength steel and greatly reduce the production cost.

[0078] It can be seen from the above examples that the present invention provides a method for constructing nano-phase hierarchies in steel and a high-toughness ultra-high-strength steel prepared at low cost. By optimizing the chemical composition ratio, adding filaments such as Al, Ti, and composite rare earths during melting, and adjusting the heat treatment process, nano-phases are hierarchically constructed step by step and temperature zone by temperature zone in the steel, thereby improving its strength, plasticity / toughness, etc., and meeting the service requirements in extreme environments. The tensile strength Rm of the high-toughness ultra-high-strength steel of the present invention is ≥2000 MPa, and the impact energy Aku is ≥70 J. The preparation method of the present invention has strong operability and controllable composition. Compared with the traditional melting and deoxidation processes, the hierarchical construction of nano-phases in the present invention is beneficial to simultaneously improve its strength and plasticity / toughness, reduce the production cost, and can be industrially promoted and applied.

[0079] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A high-toughness ultra-high-strength steel, characterized in that, The chemical composition of the high-toughness ultra-high-strength steel includes: C 0.20 - 0.25%, Si ≤ 0.02%, Mn ≤ 0.02%, Ni 8.5 - 10.5%, Cr 1.60 - 2.50%, Mo 0.9 - 1.3%, Al 0.015 - 0.025%, Co 6.5 - 8.5%, Nb 0.015 - 0.022%, Ti 0.015 - 0.02%, W ≤ 0.5%, composite rare earth elements ≤ 0.03%, P ≤ 0.01%, S ≤ 0.01%, and the balance is Fe; The composite rare earth elements include La and Ce, and the mass ratio of La to Ce is 1:

1.

2. The method for constructing the hierarchical nanostructure in the high-toughness ultra-high strength steel according to claim 1, characterized in that, It includes the following steps: 1) Mix the raw materials corresponding to the chemical composition of the high-toughness ultra-high-strength steel and conduct vacuum melting to obtain molten steel; 2) Feed composite fine wires into the molten steel, and conduct refining and casting in sequence to obtain an ingot; 3) Forge the ingot using a three-heading and three-drawing forging process, and then conduct quenching, cryogenic treatment, first medium-temperature tempering, and second low-temperature tempering in sequence to obtain the high-toughness ultra-high-strength steel.

3. The method for constructing the nano-phase hierarchy in the high-toughness ultra-high-strength steel according to claim 2, characterized in that The vacuum degree of the vacuum melting is 1 - 5 Pa, and the power of the vacuum melting is 50 - 180 kW.

4. The method for constructing the nano-phase hierarchy in the high-toughness ultra-high-strength steel according to claim 3, characterized in that, The composite fine wires include Al fine wires, Ti fine wires, and composite rare earth fine wires. Among them, the rare earth elements in the composite rare earth fine wires are La and Ce, and the mass ratio of La to Ce is 1:1; The diameter of the composite fine wires is 0.5 - 1.5 mm; The oxygen content of the composite rare earth fine wires is less than 40 ppm.

5. The method for constructing the nano-phase hierarchy in the high-toughness ultra-high-strength steel according to claim 4, wherein, The diameter of the Al fine wires is 0.5 - 1.5 mm; The diameter of the Ti fine wires is 0.5 - 1.5 mm; The diameter of the composite rare earth fine wires is 0.5 - 1.5 mm.

6. The method for constructing a nano-phase hierarchy in a high-toughness ultra-high-strength steel according to claim 4 or 5, characterized in that, The feeding speed of the composite fine wires is 0.05 - 1.5 m / s; The mass of the fed Al fine wires is 0.015 - 0.5% of the total mass of the raw materials, the mass of the fed Ti fine wires is 0.015 - 0.45% of the total mass of the raw materials, and the mass of the fed composite rare earth fine wires is 0.000 - 0.035% of the total mass of the raw materials.

7. The method for constructing the hierarchical nanostructure in the high-toughness ultra-high-strength steel according to claim 6, wherein The power of the refining is 80 - 160 kW; The vacuum degree of the casting is 1 - 5 Pa, and the power of the casting is 60 - 100 kW.

8. The method for constructing the hierarchical nanostructure in the high toughness and ultra-high strength steel according to claim 7, wherein, In the three-heading and three-drawing forging process, the initial forging temperature is 1050 - 1100 °C, the final forging temperature ≥ 950 °C, and the forging ratio ≥ 6.

9. The method for constructing the nano-phase hierarchy in the high-toughness ultra-high-strength steel according to claim 8, wherein, The temperature of the quenching is 850 - 920 °C, and the time of the quenching is 1 - 2 h; The temperature of the cryogenic treatment is -80 - -70 °C, and the time of the cryogenic treatment is 0.5 - 2 h.

10. The method for constructing the hierarchical nanostructure in the high-toughness ultra-high strength steel according to claim 9, characterized in that, The temperature of the first medium-temperature tempering is 460 - 520 °C, and the time of the first medium-temperature tempering is 4 - 6 h; The temperature of the second low-temperature tempering is 220 - 250 °C, and the time of the second low-temperature tempering is 1 - 3 h.

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