1900mpa grade super high strength and toughness stainless gear steel and preparation method thereof

Abstract

This invention relates to a 1900MPa grade ultra-high strength and toughness stainless gear steel and its preparation method. The chemical composition of the 1900MPa grade ultra-high strength and toughness stainless gear steel, by mass percentage, is: C 0.08-0.11%, Cr 10-12%, Ni 2-4%, Mo 2-5%, Co 10-13%, V 0.2-0.6%, Nb 0.02-0.05%, Al 0.5-1.0%, with the balance being Fe and unavoidable impurities. Its composition design must meet the following requirements: Chromium equivalent Cr... eq It is 17~18, with a nickel equivalent (Ni). eq The martensitic transformation point is 14-15. s The temperature range is 240~280℃. Its beneficial effects are: strengthening through the composite precipitation of intermetallic compounds NiAl and M₂C carbides, combined with Cr... eq Ni eq M s A synergistic design incorporating 5%–10% metastable austenite achieves an excellent balance between strength and toughness. The resulting steel exhibits tensile strength ≥1900 MPa, yield strength ≥1550 MPa, elongation ≥13%, fracture toughness ≥80 MPa·m¹ / ², and bending fatigue limit reaching 920 MPa. It is particularly suitable for manufacturing critical structural components requiring high load-bearing capacity and high reliability, such as aircraft engines, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, and in particular to a 1900MPa grade ultra-high strength and toughness stainless gear steel and its preparation method. Background Technology

[0002] As the aerospace industry moves towards high speed, heavy load, and lightweight design, extremely stringent performance requirements are being placed on its core transmission components, such as gears and bearings. Materials not only need to possess extremely high tensile strength to withstand extreme loads, but also sufficiently high yield strength and fatigue limit to ensure the reliability and lifespan of the components, while simultaneously exhibiting good fracture toughness and corrosion resistance.

[0003] To meet these requirements, a series of high-performance stainless gear steels have been developed both domestically and internationally. Among them, CSS-42L steel developed by Latrobe Special Steels in the United States is a typical representative of surface-hardened stainless gear steel and has been applied in aerospace transmission systems. However, its strength level (tensile strength of approximately 1714 MPa and yield strength of approximately 1350 MPa) is no longer sufficient to meet the higher requirements of the next generation of equipment for material load-bearing capacity.

[0004] Researchers have conducted extensive research on stainless gear steels with higher strength. Early patents, such as US5288347A and JP5247593A, disclosed steel grades with tensile strengths generally below 1800 MPa. Subsequent studies, through optimized heat treatment processes, such as cryogenic treatment, have increased tensile strength to 1800–1810 MPa, yield strength to 1400–1450 MPa, and fracture toughness to at least 110 MPa·m¹ / ². However, further breakthroughs beyond these strengths face the common challenge of balancing strength and toughness: simply increasing the content of carbon or strong carbide-forming elements, while improving strength, significantly reduces the martensitic transformation endpoint (Mg). f This results in excessively high residual austenite content and uncontrolled morphology, which in turn impairs yield strength and fatigue performance.

[0005] Recently, a technique for composite precipitation strengthening using NiAl intermetallic compounds and M2C carbides has been proposed (e.g., CN116397174B), providing a new direction for overcoming strength bottlenecks. This patent obtains NiAl and M2C dual nano-precipitates in steel by adding elements such as Al and Co, reporting tensile strengths exceeding 1900 MPa. However, this technique primarily focuses on the qualitative acquisition of the dual precipitates, with a wide range of compositional designs (e.g., C: 0.12-0.40%, Ni: 7.0-17.0%), and does not propose a clear quantitative control method for key factors affecting microstructure stability and yield strength, such as the content and morphology of metastable austenite. Furthermore, the patent does not disclose specific yield strength data, while yield strength is a core indicator for load-bearing design and safety assessment of engineering components. This poses a potential risk of difficulty in ensuring microstructure uniformity and large performance fluctuations when pursuing stable yield strengths above 1550 MPa and excellent fatigue resistance.

[0006] Therefore, existing technologies lack a composition design method for stainless gear steel that is based on CSS-42L, incorporates the concept of dual-phase precipitation strengthening, and can quantitatively control metastable austenite to stably achieve a yield strength of over 1550 MPa at a tensile strength of 1900 MPa. Based on this, this invention, through element matching design and process optimization, proposes a composition design and preparation method for 1900 MPa-grade ultra-high strength and toughness stainless gear steel, building upon the CSS-42L alloy system. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a compositional design scheme for low-carbon aluminum composite precipitation strengthening and multi-element equivalent synergistic microstructure control. This scheme introduces a specific amount of aluminum element, and on the basis of traditional M2C carbide strengthening, synergistically introduces a high-density nanoscale NiAl intermetallic compound phase to construct a unique biphase nanoprecipitation strengthening system; simultaneously, it precisely designs the chromium equivalent (Cr... eq ), nickel equivalent (Ni eq ) and martensitic transformation point (M s The matching model enables quantitative control of the content and morphology of metastable austenite, thereby achieving an excellent match of high tensile strength, high yield strength and high toughness at ultra-high strength levels.

[0008] The core of this invention lies in achieving a performance breakthrough through the synergistic design of the following three levels: First, a two-phase precipitation strengthening design using low-carbon aluminum. The carbon content is strictly controlled within a low range of 0.07–0.11%, providing necessary carbide reinforcement while avoiding the decrease in toughness and excessive reduction in martensitic transformation temperature caused by excessive carbon content. Simultaneously, 0.5–1.0% aluminum is added to form a high-density nanoscale NiAl intermetallic compound, which, together with the inherent M2C carbides in the matrix, constitutes a composite precipitation strengthening system. The synergistic effect of these two components not only achieves a superposition of strengthening effects but also provides heterogeneous nucleation sites for M2C through the NiAl phase, inhibiting M2C coarsening along dislocations, significantly increasing its number density and refining its size, laying the microstructure foundation for obtaining a high yield strength exceeding 1550 MPa.

[0009] Second, a multi-element equivalent synergistic organizational control model. This involves optimizing the proportions of key elements such as chromium, nickel, aluminum, molybdenum, and cobalt, and introducing the chromium equivalent (Cr). eq ), nickel equivalent (Ni eq ) and martensitic transformation point (M s A matching model is used to achieve precise control over the content and morphology of metastable austenite. This model aims to balance the strength and toughness of materials, especially ensuring the stable achievement of high yield strength. Its specific parameter design and mechanism of action will be detailed later.

[0010] Third, the design for grain refinement and stabilization using trace elements. Adding trace amounts of vanadium (0.2–0.6%) and niobium (0.02–0.05%) utilizes the pinning effect of their carbonitrides during heat treatment to further refine the grains and enhance the toughening effect.

[0011] Based on the above collaborative design, the chemical composition (mass percentage) of the steel of this invention is as follows: C: 0.08–0.11%, Cr: 10–12%, Ni: 2–4%, Mo: 2–5%, Co: 10–13%, V: 0.2–0.6%, Nb: 0.02–0.05%, Al: 0.5–1.0%, with the balance being Fe and other unavoidable impurity elements. The above composition design must simultaneously satisfy the chromium equivalent Cr defined by the following relationship. eq Nickel equivalent Ni eq and martensitic transformation point M s Within a specific range: 17 < Cr eq <18, 14 < Ni eq <15, 240℃ <M s <280℃, of which: Cr eq =[Cr]+[Mo]+0.75[W]+2.8[V]+2.5[Al] (1) Ni eq=[Ni]+30[C]+0.7[Co] (2) M s =520-423w C -12.1w Cr -17.7w Ni -7.5w Mo (3) Where [ ] represents the mass percentage of the element enclosed in curly braces, w represents the mass percentage of the element under the subscript, and the value of elements not included in the curly braces is zero.

[0012] This invention employs a secondary hardening mechanism in its composition design. Through the synergistic regulation of the aforementioned multi-parameter matching model, it achieves a lath martensite microstructure of over 90% after quenching. Following aging at 500–540℃, it yields high-density NiAl and M2C dual-phase nanoprecipitates and a thin-film reverse-transformed austenite, resulting in steel possessing both ultra-high strength of 1900 MPa and excellent strength-toughness balance. The roles and matching criteria of each element in this invention are as follows: C: A core element for solid solution strengthening, it synergistically forms MC / M2C type carbides with carbide-forming elements (Cr / V / Nb). Too low a content results in insufficient secondary hardening, while too high a content (>0.12%) impairs the toughness of the matrix and produces excessive retained austenite. Therefore, the carbon content should be controlled between 0.08-0.11%.

[0013] Cr: A key element for improving corrosion resistance, resistance to tempering softening, and hardenability. Too low a chromium content results in insufficient corrosion resistance; too high a content leads to an increase in chromium equivalent (Cr). eq Excessive Cr content can easily lead to the formation of harmful δ-ferrite and also compress the design space for elements such as Mo and Al. Therefore, the Cr content in this invention is controlled at 10-12%.

[0014] Mo: A core element for high-temperature strengthening, it precipitates M2C carbides, significantly improving secondary hardening ability, strength, and resistance to softening. Too low a molybdenum content results in insufficient secondary hardening ability; too high a content easily leads to enrichment of brittle phases, while simultaneously reducing the chromium equivalent (Cr). eq Excessive levels of Mo increase the tendency for brittleness. Therefore, the Mo content in this invention is controlled at 2–5%.

[0015] Ni: Expands the γ phase region, improves toughness and hardenability, and is the nickel equivalent (Ni eq Nickel content is a key variable and also a necessary element for the formation of NiAl precipitates. To balance toughness and retained austenite, the nickel content in this invention is controlled at 2-4%.

[0016] Al: A ferrite-forming element, it forms a high-density NiAl intermetallic compound with Ni, significantly enhancing precipitation strengthening capabilities. Excessive aluminum content leads to a decrease in chromium equivalent (Cr). eqExcessive Al content can easily lead to the formation of δ-ferrite, which impairs the toughness of the matrix. Therefore, the Al content in this invention is controlled at 0.5% to 1.0%.

[0017] Co: Promotes secondary hardening reaction, causing finer and more dispersed M2C and NiAl phases to precipitate in the steel, thus increasing strength; it can also enhance M... s To balance the tendency of austenite overstabilization caused by high Ni content, the Co content in this invention is controlled at 10-13%.

[0018] V+Nb: Strong carbide-forming elements, forming high-hardness nanoscale (Nb,V)C carbides, pinning grain boundaries and hindering dislocation movement. The addition of Nb can significantly improve the thermal stability of carbides and enhance grain refinement; however, excessive content can easily lead to carbide coarsening. Therefore, in this invention, the V content is controlled at 0.2–0.6%, and the Nb content is controlled at 0.02–0.05%.

[0019] Chromium equivalent (Cr) eq The model aims to integrate the effects of all ferrite-forming elements, precisely suppressing the precipitation of harmful δ-ferrite while ensuring corrosion resistance, thus guaranteeing a pure martensitic matrix. This invention controls the chromium equivalent to 17–18.

[0020] Nickel equivalent (Ni eq The model is used to precisely control the content of retained austenite and reverse-transformed austenite (target 5-10 vol%), distributing them in a thin film morphology of ≤100 nm at the martensite lath boundaries, thereby significantly improving the fracture toughness of the material without excessively sacrificing yield strength. This invention controls the nickel equivalent at 14-15%.

[0021] Martensitic transformation point (M s The design temperature is 240–280℃. Higher M s This ensures that a high proportion (>90%) of martensite is obtained after quenching, while minimizing blocky retained austenite (<5%) that does not contribute to strength. This is crucial for achieving high yield strength (Rp). 0.2 Key organizational support (≥1550MPa).

[0022] The preparation method of the steel used in this invention: (1) Melting and casting ingots: Vacuum induction melting is adopted and the ingots are cast into steel ingots; Vacuum induction (VIM) and vacuum arc remelting (VAR) dual vacuum smelting can be selected; (2) Homogenization treatment: The steel ingot is subjected to diffusion annealing at 1200-1250℃ for 20-30 hours; (3) Forging: Heat the ingot to 1200~1250℃, the initial forging temperature is ≤1180℃, the final forging temperature is ≥900℃, and the cumulative forging ratio is 8~10.

[0023] (4) Annealing: After forging, keep it at 850-1000℃, slowly cool it to 630-670℃ and keep it at that temperature for 25 hours, then furnace cool it to below 200℃ and air cool it.

[0024] The pre-hardening heat treatment process for stainless gear steel is as follows: Quenching treatment: Hold at 1060℃~1080℃ for 1~2 hours, then oil quench to room temperature; Cryogenic treatment: Keep warm at a temperature below -73℃ for 4–8 hours, then air cool to room temperature; Aging intensification treatment: Keep at 500-540℃ for 4-10 hours, then air cool to room temperature.

[0025] The implementation of this invention has the following technical effects: Compared with existing technologies, this invention breaks through the limitations of existing ultra-high strength stainless gear steels that mainly rely on the precipitation strengthening of single M2C carbides, and proposes a "low carbon medium aluminum" combined with Cr eq / Ni eq / M s The systematic design method of the multi-parameter quantitative model achieves a significant improvement over single-phase precipitation (single M2C) in two-phase precipitation (NiAl+M2C), and enables precise control over the toughening phase (thin-film austenite). Specifically: First, a mutually reinforcing mechanism for NiAl and M2C biphase nanoprecipitations was constructed, with a significantly better strengthening effect than the single M2C system. This invention, by introducing 0.5–1.0% aluminum, induces the preferential precipitation of high-density nanoscale NiAl intermetallic compounds on the basis of traditional M2C carbide reinforcement, providing a large number of heterogeneous nucleation sites for M2C. Unlike single M2C precipitation, which tends to coarsen along dislocations, the number density and size of M2C in this invention are significantly improved, achieving a comprehensive advantage of biphase precipitation in terms of quantity, size, and distribution over single-phase precipitation. Under this synergistic strengthening effect, this invention lays the microstructural foundation for obtaining a high yield strength of over 1550 MPa.

[0026] Second, quantitative control of the content and morphology of metastable austenite was achieved. This was accomplished through chromium equivalent (Cr... eq =17~18), nickel equivalent (Ni eq =14~15) and martensitic transformation point (M s The present invention uses a matching model (240~280℃) to precisely control the content (5~10%) and distribution morphology (≤100 nm thin film distribution at the martensite lath boundary) of residual austenite after quenching and during the aging process. While ensuring high yield strength, it significantly improves the fracture toughness and fatigue resistance of the material.

[0027] Based on the aforementioned synergistic strengthening and organizational regulation mechanism, this invention not only achieves ultra-high strength of ≥1900 MPa tensile strength, but also sets a high target value of ≥1550 MPa yield strength, while taking into account excellent performance of fracture toughness >80 MPa·m¹ / ² and bending fatigue limit ≥900 MPa. For the first time, it has achieved a synergistic breakthrough of high yield strength, high toughness and high fatigue limit at the 1900 MPa strength level. The overall performance is significantly better than that of existing materials, and it has important application value in aerospace, high-end equipment and other fields. Attached Figure Description

[0028] Figure 1 The metallographic structure of the 1900MPa grade ultra-high strength and toughness stainless gear steel in Embodiment 1 of the present invention is shown.

[0029] Figure 2 These are NiAl+M2C precipitates in the 1900MPa grade ultra-high strength and toughness stainless gear steel of Example 1 of this invention.

[0030] Figure 3 This is a phase distribution diagram of the EBSD phase in the 1900MPa grade ultra-high strength and toughness stainless gear steel of Embodiment 1 of the present invention.

[0031] Figure 4 The microstructure of the 1900MPa grade ultra-high strength and toughness stainless gear steel is the interlamellar reverse transformation austenite microstructure. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the embodiments and accompanying drawings. It should be noted that the described embodiments are only intended to facilitate the understanding of the present invention and do not constitute any limitation thereof. Example 1

[0033] The present embodiment of a method for preparing 1900MPa grade ultra-high strength and toughness stainless gear steel includes the following steps: (1) Smelting and casting ingots: According to the chemical composition range designed according to the present invention, the No. 1 steel of this embodiment is smelted in a 25kg vacuum induction furnace and cast into steel ingots. The specific chemical composition is shown in Table 1. (2) Homogenization treatment: The steel ingot is subjected to diffusion annealing at 1200℃ and held for 30h; (3) Forging: Heat the ingot to 1200℃, the initial forging temperature is ≤1180℃, the final forging temperature is ≥900℃, and the cumulative forging ratio is 8~10.

[0034] (4) Annealing: After forging, keep it at 850℃, slowly cool it to 670℃ and keep it at that temperature for 25 hours, then furnace cool it to below 200℃ and air cool it.

[0035] The pre-hardening heat treatment process is as follows: Quenching treatment: Hold at 1060℃ for 1 hour, then oil quench to room temperature; Cryogenic treatment: Hold at -73℃ for 8 hours, then air cool to room temperature; Aging intensification treatment: Keep at 500℃ for 8 hours, then air cool to room temperature.

[0036] Figures 1 to 4 The metallographic structure of the gear steel in this embodiment, NiAl+M2C precipitates, EBSD phase distribution diagram, and interlamellar reverse transformation austenite are shown. Example 2

[0037] The present embodiment of a method for preparing 1900MPa grade ultra-high strength and toughness stainless gear steel includes the following steps: (1) Smelting and casting ingots: According to the chemical composition range designed according to the present invention, the No. 2 steel of this embodiment is smelted in a 25kg vacuum induction furnace and cast into steel ingots. The specific chemical composition is shown in Table 1. (2) Homogenization treatment: The steel ingot is subjected to diffusion annealing at 1230℃ for 25 hours; (3) Forging: Heat the ingot to 1230℃, start forging temperature ≤1180℃, end forging temperature ≥900℃, and the cumulative forging ratio is 8~10.

[0038] (4) Annealing: After forging, keep it at 930℃, slowly cool it to 650℃ and keep it at 650℃ for 25 hours, then furnace cool it to below 200℃ and air cool it.

[0039] The pre-hardening heat treatment process is as follows: Quenching treatment: Hold at 1060℃ for 1 hour, then oil quench to room temperature; Cryogenic treatment: Hold at -73℃ for 8 hours, then air cool to room temperature; Aging intensification treatment: Keep at 500℃ for 8 hours, then air cool to room temperature.

[0040] The metallographic structure, NiAl+M2C precipitates, EBSD phase distribution, and interlamellar reverse transformation austenite of the gear steel in this embodiment are similar to those in Example 1, and will not be described again. Example 3

[0041] The present embodiment of a method for preparing 1900MPa grade ultra-high strength and toughness stainless gear steel includes the following steps: (1) Smelting and casting ingots: According to the chemical composition range designed according to the present invention, the No. 3 steel of this embodiment is smelted in a 25kg vacuum induction furnace and cast into steel ingots. The specific chemical composition is shown in Table 1. (2) Homogenization treatment: The steel ingot is subjected to diffusion annealing at 1250℃ for 20h; (3) Forging: Heat the ingot to 1250℃, the initial forging temperature is ≤1180℃, the final forging temperature is ≥900℃, and the cumulative forging ratio is 8~10.

[0042] (4) Annealing: After forging, keep it at 1000℃, slowly cool it to 630℃ and keep it at that temperature for 25 hours, then furnace cool it to below 200℃ and air cool it.

[0043] The pre-hardening heat treatment process is as follows: Quenching treatment: Hold at 1060℃ for 1 hour, then oil quench to room temperature; Cryogenic treatment: Hold at -73℃ for 8 hours, then air cool to room temperature; Aging intensification treatment: Keep at 500℃ for 8 hours, then air cool to room temperature.

[0044] The metallographic structure, NiAl+M2C precipitates, EBSD phase distribution, and interlamellar reverse transformation austenite of the gear steel in this embodiment are similar to those in Example 1, and will not be described again. Example 4

[0045] The present embodiment of a method for preparing 1900MPa grade ultra-high strength and toughness stainless gear steel includes the following steps: (1) Smelting and casting ingots: According to the chemical composition range designed according to the present invention, the No. 4 steel of this embodiment is smelted in a 25kg vacuum induction furnace and cast into steel ingots. The specific chemical composition is shown in Table 1. (2) Homogenization treatment: The steel ingot is subjected to diffusion annealing at 1210℃ for 28 hours; (3) Forging: Heat the ingot to 1200℃, the initial forging temperature is ≤1180℃, the final forging temperature is ≥900℃, and the cumulative forging ratio is 8~10.

[0046] (4) Annealing: After forging, keep it at 850℃, slowly cool it to 670℃ and keep it at that temperature for 25 hours, then furnace cool it to below 200℃ and air cool it.

[0047] The pre-hardening heat treatment process is as follows: Quenching treatment: Hold at 1070℃ for 2 hours, then oil quench to room temperature; Cryogenic treatment: Hold at -73℃ for 6 hours, then air cool to room temperature; Aging intensification treatment: Keep at 520℃ for 10 hours, then air cool to room temperature.

[0048] The metallographic structure, NiAl+M2C precipitates, EBSD phase distribution, and interlamellar reverse transformation austenite of the gear steel in this embodiment are similar to those in Example 1, and will not be described again. Example 5

[0049] The present embodiment of a method for preparing 1900MPa grade ultra-high strength and toughness stainless gear steel includes the following steps: (1) Smelting and casting ingots: According to the chemical composition range designed according to the present invention, the No. 5 steel of this embodiment is smelted in a 25kg vacuum induction furnace and cast into steel ingots. The specific chemical composition is shown in Table 1. (2) Homogenization treatment: The steel ingot is subjected to diffusion annealing at 1200℃ for 28 hours; (3) Forging: Heat the ingot to 1200℃, the initial forging temperature is ≤1180℃, the final forging temperature is ≥900℃, and the cumulative forging ratio is 8~10.

[0050] (4) Annealing: After forging, keep it at 850℃, slowly cool it to 670℃ and keep it at that temperature for 25 hours, then furnace cool it to below 200℃ and air cool it.

[0051] The pre-hardening heat treatment process is as follows: Quenching treatment: Hold at 1080℃ for 1.5h, then oil quench to room temperature; Cryogenic treatment: Hold at -73℃ for 4 hours, then air cool to room temperature; Aging intensification treatment: Keep at 540℃ for 4 hours, then air cool to room temperature.

[0052] The metallographic structure, NiAl+M2C precipitates, EBSD phase distribution, and interlamellar reverse transformation austenite of the gear steel in this embodiment are similar to those in Example 1, and will not be described again.

[0053] The room temperature mechanical properties and fatigue properties of Examples 1-5 are shown in Table 2. Not only did they achieve ultra-high strength with tensile strength ≥1900 MPa, but they also set a high target value of yield strength ≥1550 MPa. Furthermore, they took into account excellent properties such as fracture toughness >80 MPa·m¹ / ² and bending fatigue limit ≥900 MPa. For the first time, they achieved a synergistic breakthrough of high yield strength, high toughness and high fatigue limit at the 1900 MPa strength level. The overall performance is significantly better than that of existing materials, and it has important application value in aerospace, high-end equipment and other fields.

[0054]

[0055]

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A 1900MPa grade ultra-high strength and toughness stainless gear steel, characterized in that, The chemical composition in terms of mass percentage is: C: 0.08-0.11%, Cr: 10-12%, Ni: 2-4%, Mo: 2-5%, Co: 10-13%, V: 0.2-0.6%, Nb: 0.02-0.05%, Al: 0.5-1.0%, and the balance of Fe and inevitable impurities; and the chemical composition of the steel satisfies the chromium equivalent Cr eq of 17-18, the nickel equivalent Ni eq of 14-15, the martensite transformation point M s of 240-280°C: Cr eq =[Cr]+[Mo]+0.75[W]+2.8[V]+2.5[Al] (1) Ni eq =[Ni]+30[C]+0.7[Co] (2) M s =520-423w C -12.1w Cr -17.7w Ni -7.5w Mo (3) Where [ ] represents the mass percentage of the element enclosed in curly braces, w represents the mass percentage of the element under the subscript, and the value of elements not included in the curly braces is zero.

2. A method for preparing the 1900MPa grade ultra-high strength and toughness stainless gear steel according to claim 1, characterized in that, Includes the following steps: (1) Melting and casting ingots: Vacuum induction melting is used to cast steel ingots; (2) Homogenization treatment: The steel ingot is subjected to diffusion annealing at 1200-1250℃ for 20-30 hours; (3) Forging: Heat the ingot to 1200-1250℃, start forging temperature ≤1180℃, end forging temperature ≥900℃, and the cumulative forging ratio is 8-10; (4) Annealing: After forging, keep it at 850~1000℃, then cool it to 630~670℃ and keep it at 25h. Then, furnace cool it to below 200℃ and air cool it.

3. A method for preparing 1900MPa grade ultra-high strength and toughness stainless gear steel according to claim 2, characterized in that: The pre-hardening heat treatment process is as follows: Quenching treatment: Hold at 1060~1080℃ for 1~2h, then oil quench to room temperature; Cryogenic treatment: Keep warm at a temperature below -73℃ for 4–8 hours, then air cool to room temperature; Aging intensification treatment: Keep at 500-540℃ for 4-10 hours, then air cool to room temperature.

4. A method for preparing 1900MPa grade ultra-high strength and toughness stainless gear steel according to claim 2, characterized in that: The pre-hardened heat-treated gear steel has a tensile strength ≥1900MPa, a yield strength ≥1550MPa, a hardness ≥55 HRC, and a fracture toughness ≥80MPa·m. 1 / 2 The bending fatigue limit reaches 920 MPa.

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