Martensitic age-hardened steel with synergistic optimization of high strength and high toughness and method of manufacturing the same

Abstract

This invention relates to the field of steel materials technology, and discloses a high-strength and high-toughness synergistically optimized martensitic aging steel and its preparation method. The martensitic aging steel comprises, by mass percentage: Co: 15.5~17.0%, Ni: 17.0~19.0%, Mo: 6.0~8.0%, Ti: 1.0~2.0%, Al: 0.5~1.0%, Mn: 0.1~0.5%, Zr: 0.01~0.05%, with the balance being Fe and unavoidable impurities. This invention can synergistically improve the strength and toughness of martensitic aging steel while reducing the difficulty of its preparation.

Description

Technical Field

[0001] This invention relates to the field of steel materials technology, specifically to a high-strength-high-toughness synergistically optimized martensitic aging steel and its preparation method. Background Technology

[0002] Martensitic aging steel, possessing both ultra-high strength and good plasticity, is widely used in high-end manufacturing fields such as aerospace and communications. With the increasing demands for lightweight structures and performance limits in these fields, steel, as a relatively high-density structural material, is facing increasingly stringent comprehensive performance challenges. Therefore, developing martensitic aging steel with both ultra-high strength and high plasticity is of significant engineering and application value for promoting the performance upgrade of my country's aerospace and communication equipment. The external dimensions of materials (such as bars, wires, and plates) have a significant impact on their microstructure evolution and mechanical properties, and different application scenarios have significantly different requirements for material dimensions and forming methods. Therefore, developing martensitic aging steel that can adapt to various external dimension conditions and simultaneously meet the requirements of ultra-high strength (Rm≥2650MPa, Rp0.2≥2400MPa) and high plasticity (elongation>6.0%) has become a critical issue that urgently needs to be addressed.

[0003] Patent CN109112425A discloses an ultra-high strength and high toughness martensitic aging steel, its preparation method, and its application. The chemical composition of the martensitic aging steel, by mass content, is as follows: Ni: 18.0-20.0%, Co: 15.0-18.0%, Mo: 7.0-8.0%, Ti: 1.5-2.5%, Cu: 4.0-6.0%, C < 0.005%, O < 0.001%, N < 0.002%, P < 0.001%, S < 0.001%, with the balance being Fe; the total content of C, O, N, P, and S is < 0.01%. The martensitic aging steel forms a copper-rich phase and a Ni3Ti core-shell structure, exhibiting a tensile strength > 3000 MPa, a yield strength > 2700 MPa, and an elongation > 10%. However, the addition of a high Cu content to this martensitic aging steel makes it prone to segregation at grain boundaries, leading to hot brittleness and increasing the difficulty of smelting and hot working. The high Ti content increases the risk of generating brittle TiN particles, thus reducing the difficulty of preparation.

[0004] Patent CN105568151A discloses an aluminum-reinforced martensitic aging steel and its preparation method. The composition of this aluminum-reinforced martensitic steel, by weight percentage, is: C: 0.01-0.2%, Ni: 6-24%, Mo: ≤6%, Mn: 0-4%, Al: 0.5-6%, Cr: 0-12%, Nb: 0-1.5%, Cu: 0-4%, W: 0-3%, B: 0.0005-0.05%, with the balance being Fe and unavoidable impurities. According to the feeding and smelting process, followed by forging, solution treatment, and cold rolling heat treatment, a martensitic aging steel with uniform microstructure and high density, primarily reinforced by B2-NiAl intermetallic compounds, and reinforced by trace amounts of carbides and nanoclusters, is prepared. It exhibits excellent mechanical properties, with a tensile strength reaching 2.2 GPa. However, this martensitic aging steel contains a high content of C and Nb, which easily forms NbC carbides. There is a risk that the plasticity and toughness of the steel may be compromised due to poor control of carbide size. Moreover, its tensile strength is 2.2 GPa, which is difficult to meet the requirements for higher strength (≥2650 MPa).

[0005] Patent CN115558853A discloses a high-strength and high-toughness martensitic aging steel and its preparation method. The composition of this high-strength and high-toughness martensitic aging steel, by mass percentage, includes: C≤0.02%, Si≤0.5%, Mn≤0.5%, P≤0.020%, S≤0.005%, Cr: 11.0~13.0%, Ni: 8.0~10.0%, Mo: 3.0~5.0%, Cu: 1.0~3.0%, Ti: 0.5~1.5%, Al: 0.1~0.8%, Ce: 0.001~0.010%, Nb: 0.10~0.30%, with the balance being Fe and unavoidable impurities. However, this martensitic aging steel belongs to the martensitic aging stainless steel system, and its strength depends on the amount of cold working deformation. It is difficult to stably achieve high strength without cold rolling, and the cold rolling process increases the risk of cracking and the difficulty of preparation.

[0006] Therefore, existing technologies still need improvement. Summary of the Invention

[0007] The main objective of this invention is to provide a high-strength and high-toughness synergistically optimized martensitic aging steel and its preparation method, in order to solve the technical problem of how to synergistically improve the strength and toughness of martensitic aging steel and reduce its preparation difficulty.

[0008] According to one aspect of the present invention, a high-strength and high-toughness synergistically optimized martensitic aging steel is proposed, comprising, by mass percentage: Co: 15.5~17.0%, Ni: 17.0~19.0%, Mo: 6.0~8.0%, Ti: 1.0~2.0%, Al: 0.5~1.0%, Mn: 0.1~0.5%, Zr: 0.01~0.05%, with the balance being Fe and unavoidable impurities.

[0009] According to one embodiment of the present invention, the martensitic aging steel has a grain size ≥ 8.0, a tensile strength ≥ 2650 MPa, a yield strength ≥ 2400 MPa, and an elongation > 6%.

[0010] According to one embodiment of the present invention, the impurity element content in the martensitic aging steel is as follows, by mass percentage: C≤0.008%, Si≤0.1%, P≤0.005%, S≤0.005%, N≤0.0015%, O≤0.0015%.

[0011] According to another aspect of the present invention, a method for preparing martensitic aging steel as described above is provided, comprising: sequentially performing smelting, homogenization treatment, forging, hot deformation, and heat treatment to obtain martensitic aging steel.

[0012] According to one embodiment of the present invention, the smelting process includes: using a combination of vacuum induction and vacuum consumable processes to obtain a martensitic aging steel ingot.

[0013] According to one embodiment of the present invention, the homogenization process includes: holding at a temperature of 1250~1260°C for 36~60 hours.

[0014] According to one embodiment of the present invention, the forging process includes: performing multiple upsetting and drawing operations; wherein the initial forging temperature is 1180~1200℃, and the final forging temperature is ≥1000℃; the reduction amount of each upsetting operation is ≥50%, and the drawing rate of each drawing operation is ≥200%; when the temperature is below 1050℃, the furnace is returned to the furnace and heated at 1100~1200℃ for 1~3 hours before continuing upsetting; when the temperature is below 1000℃, the furnace is returned to the furnace and heated at 1050~1150℃ for 1~3 hours before continuing drawing.

[0015] According to one embodiment of the present invention, hot deformation includes: reheating the forged material after forging to 1100~1200℃ and holding it at that temperature for 1~3h, and then precision forging or rolling it to the target size; wherein the single-pass reduction of precision forging or rolling is ≤35%, and the final forging or final rolling temperature is ≥950℃.

[0016] According to one embodiment of the present invention, the heat treatment includes: holding at 850~860°C for 1~2 hours, then oil cooling to room temperature; holding at 820~830°C for 1~1.5 hours, then oil cooling to room temperature, repeating this process at least once; cooling in a cryogenic device at -70~-80°C for 1~2 hours, then naturally warming in air; and aging the material after it has warmed to room temperature at an aging temperature of 480~500°C for 5~8 hours.

[0017] According to one embodiment of the present invention, the material cooled to room temperature by oil is placed in a cryogenic device for cooling within 4 hours; the material warmed back to room temperature is subjected to aging treatment within 8 hours.

[0018] In the technical solution of this invention, by designing the chemical composition of martensitic aging steel, the formation and enrichment of Ni3(Mo,Ti) precipitates can be promoted during the aging process. This enables the steel to achieve a tensile strength Rm≥2650MPa, a yield strength Rp0.2≥2400MPa, and an elongation A>6% with a grain size ≥8.0. This achieves a synergistic improvement in strength and toughness, and avoids problems such as Cu segregation, carbide damage, and cold rolling cracking, thereby reducing the difficulty of preparation. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A flowchart illustrating a method for preparing a high-strength-high-toughness synergistically optimized martensitic aging steel according to an embodiment of the present invention is shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0022] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0023] This invention proposes a high-strength and high-toughness synergistically optimized martensitic aging steel, comprising, by mass percentage: Co: 15.5~17.0%, Ni: 17.0~19.0%, Mo: 6.0~8.0%, Ti: 1.0~2.0%, Al: 0.5~1.0%, Mn: 0.1~0.5%, Zr: 0.01~0.05%, with the balance being Fe and unavoidable impurities. In some embodiments, the impurity element content in the martensitic aging steel, by mass percentage, is: C≤0.008%, Si≤0.1%, P≤0.005%, S≤0.005%, N≤0.0015%, O≤0.0015%.

[0024] This invention is based on machine learning and thermodynamic calculations to study the influence of elemental doping on precipitates in martensitic aging steel. Guided by increasing the Ni3(Mo,Ti) precipitate content during aging treatment, the chemical composition of martensitic aging steel is designed to rationally increase the content of alloying elements such as Mn, Mo, and Co, while avoiding the use of elements such as Cu and Nb. This achieves synergistic optimization of microstructure and properties, promoting the formation and enrichment of Ni3(Mo,Ti) precipitates during aging treatment. This allows the steel to achieve a tensile strength Rm ≥ 2650 MPa, a yield strength Rp0.2 ≥ 2400 MPa, and an elongation A > 6% with a grain size ≥ 8.0, thus achieving a synergistic improvement in strength and toughness. Furthermore, it avoids problems such as Cu segregation, carbide damage, and cold rolling cracking, thereby reducing the difficulty of preparation. The material proposed in this invention can be widely applied in fields such as aerospace and 3C electronics, which have stringent requirements for high-strength and high-toughness materials.

[0025] Compared with patent CN109112425A, this application removes Cu, reduces Ti, and adds Al to enhance precipitation strengthening, while adding a small amount of Mn to strengthen the steel matrix. The removal of Cu avoids the risk of Cu enrichment at grain boundaries, reducing preparation difficulty; the moderate reduction of Ti reduces the risk of Ti reacting with N to form brittle TiN particles, further reducing preparation difficulty; the addition of Al facilitates the formation of Ni3(Mo,Ti) composite precipitates, providing precipitation strengthening, while the addition of a small amount of Mn strengthens the steel matrix.

[0026] Compared with patent CN105568151A, this application adopts an ultra-low carbon design, avoiding the adverse effects of carbon content on processing performance, and can also greatly improve the plasticity and toughness of steel; this application does not add alloying element Nb, but uses trace Zr element to refine the as-cast structure, reducing the risk that NbC carbide will harm the plasticity and toughness of steel due to poor size control; this application does not use Cr and W elements, but adds Co and Ti, and increases the content of Mo to promote the formation of nanoscale Ni3(Mo,Ti) composite precipitates, while the composite precipitates can also alleviate the brittleness of Ni3Mo.

[0027] Compared with patent CN115558853A, this application has a higher content of Mo and Ti elements to increase the number of precipitates, and adds 15.5~17.0% of Co elements to promote the precipitation of Mo elements in the form of precipitates during the aging process, thereby improving the precipitation strengthening effect; and this application improves the ductility and toughness of steel by increasing the Ni element content.

[0028] In the martensitic aging steel of the present invention, the content of Co element, by mass percentage, can be 15.5%, 15.7%, 16.0%, 16.2%, 16.5%, 16.7%, or 17.0%; the content of Ni element can be 17.0%, 17.2%, 17.5%, 17.7%, 18.0%, 18.2%, 18.5%, 18.7%, or 19.0%; and the content of Mo element can be 6.0%, 6.2%, 6.5%, 6.7%, or 7.0%. The contents of elements are 7.2%, 7.5%, 7.7%, and 8.0%; the contents of elements with Ti can be 1.0%, 1.2%, 1.5%, 1.7%, and 2.0%; the contents of elements with Al can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1.0%; the contents of elements with Mn can be 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%; and the contents of elements with Zr can be 0.01%, 0.02%, 0.03%, 0.04%, and 0.05%.

[0029] refer to Figure 1 The present invention also proposes a method for preparing martensitic aging steel as described above, comprising: sequentially performing smelting, homogenization treatment, forging, hot deformation, and heat treatment to obtain martensitic aging steel.

[0030] In some embodiments, the smelting process includes: smelting a maraging steel ingot using a dual process of vacuum induction and vacuum consumables, followed by a peeling process on the maraging steel ingot. The dual process of vacuum induction and vacuum consumables can effectively remove gases and harmful impurities, precisely control the alloy composition, reduce the content of non-metallic inclusions, and decrease element segregation, thereby obtaining a maraging steel ingot with a dense structure, uniform composition, and high purity.

[0031] In some embodiments, the homogenization treatment includes: holding at a temperature of 1250~1260°C for 36~60 hours, and then removing from the furnace and cooling to the forging temperature for forging. The homogenization treatment effectively promotes the full and uniform diffusion of alloying elements, while dissolving coarse non-equilibrium phases, creating conditions for obtaining a uniform and fine microstructure during subsequent forging and heat treatment.

[0032] In some embodiments, the forging process includes: multiple upsetting and drawing operations; wherein the initial forging temperature is 1180~1200℃, and the final forging temperature is ≥1000℃; the reduction in each upsetting operation is ≥50%, and the elongation rate in each drawing operation is ≥200%; when the temperature is below 1050℃, the steel is reheated at 1100~1200℃ for 1~3 hours before continuing upsetting; when the temperature is below 1000℃, the steel is reheated at 1050~1150℃ for 1~3 hours before continuing drawing. This invention fully breaks down the as-cast structure and welds internal pores through large plastic deformation, combined with a high-temperature forging process of 1180~1200℃ and a reheating process, ensuring that the steel material always deforms within a good plastic range, avoiding cracking due to temperature drop, thereby obtaining a uniform and dense forging material.

[0033] In some embodiments, hot deformation includes: reheating the forged material after forging to 1100~1200°C and holding it at that temperature for 1~3 hours to homogenize its microstructure and restore its good thermoplasticity; then precision forging or rolling it to the target size, wherein the single-pass reduction of precision forging or rolling is ≤35%, and the final forging or rolling temperature is ≥950°C, which can avoid the risk of cracking caused by excessive single-pass deformation or low final temperature, and at the same time refine the grains through dynamic recrystallization to obtain a product with accurate dimensions and uniform microstructure.

[0034] In some embodiments, the heat treatment includes: holding at 850~860℃ for 1~2 hours, then oil cooling to room temperature; holding at 820~830℃ for 1~1.5 hours, then oil cooling to room temperature, repeating this process at least once; cooling in a cryogenic apparatus at -70~-80℃ for 1~2 hours, then removing it from the cryogenic apparatus and allowing it to warm naturally in air; and aging the material after it has warmed to room temperature at an aging temperature of 480~500℃ for 5~8 hours. This heat treatment process fully homogenizes the microstructure and refines the grains through two-stage solution treatment (high temperature + medium temperature), followed by cryogenic treatment to promote the transformation of retained austenite to martensite, and finally aging treatment to cause nanoscale Ni3(Mo,Ti) precipitates to disperse in the martensitic matrix, resulting in a strong precipitation strengthening effect.

[0035] In some embodiments, the material cooled to room temperature by oil is placed in a cryogenic device for cooling within 4 hours to prevent the austenite from becoming stable due to excessive residence time, making it difficult to transform into martensite in subsequent cryogenic treatment; the material warmed to room temperature is subjected to aging treatment within 8 hours to prevent excessive residence at room temperature from causing natural aging, and to ensure that the nanoscale precipitates can be uniformly dispersed and precipitated during the aging process.

[0036] The following description is based on specific embodiments and comparative examples.

[0037] Example 1 This embodiment provides a method for preparing martensitic aging ultra-high strength steel, the specific steps of which are as follows: Step 1: Vacuum smelting Martensitic aging steel ingots were smelted using a dual process of vacuum induction and vacuum arc remelting; the ingots were then subjected to a peeling treatment. The alloying element composition of the martensitic aging steel ingot was: Co: 15.5%, Ni: 17.7%, Mo: 7.12%, Ti: 1.45%, Al: 0.5%, Mn: 0.5%, Zr: 0.02%, with the balance being Fe and unavoidable impurities. The contents of key impurity elements were: C: 0.003%, Si: 0.01%, P: 0.0018%, S: 0.0010%, N: 0.0010%, O: 0.0012%.

[0038] Step 2: High-temperature homogenization After the peeling process, the martensitic aging steel ingot is placed in a furnace at a temperature of 1000℃ for high-temperature homogenization. The homogenization conditions include: a holding temperature of 1250℃ and a holding time of 60 hours. After the holding time, the ingot is removed from the furnace and cooled to a forging temperature of 1200℃ before forging.

[0039] Step 3: Forging and blanking The forging process employs a "three-upsetting and three-drawing" method. The initial forging temperature is 1200℃. The first upsetting reduces the material by 55% and draws it out by 250%. The second upsetting reduces the material by 55% and draws it out by 250%. The third upsetting reduces the material by 50% and draws it out by 200%. The resulting billet is a round bar with a diameter of φ300mm.

[0040] Step 4: Thermal Deformation The round bar forgings obtained after the above-mentioned "three upsetting and three drawing" process are reheated in the furnace to 1150℃ and held for 2 hours. Then, they are precision forged. The first pass of precision forging has a reduction of 30%, and the subsequent passes have a reduction of 10%, finally obtaining a round bar with a diameter of φ50mm. The final forging temperature is 960℃.

[0041] Step 5: Heat Treatment The heat treatment process is as follows: hold at 860℃ for 1 hour, then immediately oil cool to room temperature; hold at 820℃ for 1 hour, then immediately oil cool to room temperature, repeat twice; place in a -73℃ cryogenic device for 1.5 hours within 4 hours, then remove from the cryogenic device and allow to warm up naturally in the air; aging the material after it has warmed up to room temperature for 8 hours, with an aging temperature of 485℃ and a time of 5 hours.

[0042] Example 2 This embodiment provides a method for preparing martensitic aging ultra-high strength steel, the specific steps of which are as follows: Step 1: Vacuum smelting Martensitic aging steel ingots were smelted using a dual process of vacuum induction and vacuum arc remelting, followed by a peeling process. The alloy composition of the martensitic aging steel ingot is as follows: Co: 16.0%, Ni: 18.0%, Mo: 7.80%, Ti: 1.10%, Al: 0.7%, Mn: 0.2%, Zr: 0.01%, with the balance being Fe and unavoidable impurities. The contents of key impurity elements are: C: 0.002%, Si: 0.02%, P: 0.0015%, S: 0.0012%, N: 0.0007%, O: 0.0010%.

[0043] Step 2: High-temperature homogenization The martensitic aging steel ingots that have undergone peeling are placed in a furnace at a temperature of 1000℃ for high-temperature homogenization. The homogenization conditions include: a holding temperature of 1280℃ and a holding time of 36 hours. After the holding time, the ingots are removed from the furnace and cooled to a forging temperature of 1200℃ before forging.

[0044] Step 3: Forging and blanking The forging process employs a "three-upset, three-drawing" method. The initial forging temperature is 1200℃. The first upset has a reduction of 60% and a drawout rate of 300%. The second upset has a reduction of 55% and a drawout rate of 250%. The third upset has a reduction of 50% and a drawout rate of 200%. The resulting billet is a slab with a length, width, and height of 3000, 1000, and 500 mm, respectively.

[0045] Step 4: Thermal Deformation The slab forgings obtained after the above-mentioned "three upsetting and three drawing" process are reheated in the furnace to 1150℃ and held for 2 hours. Then, they are rolled out of the furnace with a reduction of 20% in the first rolling pass and 10% in subsequent rolling passes, finally obtaining a 20mm thick plate at a final rolling temperature of 950℃.

[0046] Step 5: Heat Treatment The heat treatment process is as follows: hold at 850℃ for 2 hours, then immediately oil cool to room temperature; hold at 820℃ for 1 hour, then immediately oil cool to room temperature, repeat twice; place in a -73℃ cryogenic device for 2 hours within 4 hours, then remove from the cryogenic device and allow to warm up naturally in the air; aging the material after it has warmed up to room temperature within 8 hours, with an aging temperature of 480℃ and a time of 7 hours.

[0047] Comparative Example 1 This comparative example provides a method for preparing martensitic aging ultra-high strength steel, the specific steps of which are as follows: Step 1: Vacuum smelting Martensitic aging steel ingots were smelted using a dual process of vacuum induction and vacuum consumables, followed by a peeling process. The alloy composition of the martensitic aging steel ingot is as follows: Co: 12.0%, Ni: 18.2%, Mo: 4.53%, Ti: 1.43%, Al: 0.12%, with the balance being Fe and unavoidable impurities. The contents of key impurity elements are: C: 0.0011%, Si: 0.009%, Mn: 0.01%, P: 0.0013%, S: 0.0016%, N: 0.0011%, O: 0.0008%.

[0048] Step 2: High-temperature homogenization The martensitic aging steel ingots that have undergone peeling are placed in a furnace at a temperature of 1000℃ for high-temperature homogenization. The homogenization conditions include: a holding temperature of 1250℃ and a holding time of 48 hours. After the holding time, the ingots are removed from the furnace and cooled to a forging temperature of 1200℃ before forging.

[0049] Step 3: Forging and blanking The forging process employs a "three-upsetting and three-drawing" method. The initial forging temperature is 1200℃. The first upsetting reduces the material by 55% and draws it out by 250%. The second upsetting reduces the material by 55% and draws it out by 250%. The third upsetting reduces the material by 50% and draws it out by 200%. The resulting billet is a round bar with a diameter of φ300mm.

[0050] Step 4: Thermal Deformation The round bar forgings obtained after the above-mentioned "three upsetting and three drawing" process are reheated in the furnace to 1150℃ and held for 2 hours. Then, they are precision forged. The first pass of precision forging has a reduction of 30%, and the subsequent passes have a reduction of 10%, finally obtaining a round bar with a diameter of φ50mm. The final forging temperature is 960℃.

[0051] Step 5: Heat Treatment The heat treatment process is as follows: hold at 860℃ for 1 hour, then immediately oil cool to room temperature; hold at 820℃ for 1 hour, then immediately oil cool to room temperature, repeat twice; place in a -73℃ cryogenic device for 1.5 hours within 4 hours, then remove from the cryogenic device and allow to warm up naturally in the air; aging the material after it has warmed up to room temperature for 8 hours, with an aging temperature of 485℃ and a time of 5 hours.

[0052] Comparative Example 2 This comparative example provides a method for preparing martensitic aging ultra-high strength steel, the specific steps of which are as follows: Step 1: Vacuum smelting Martensitic aging steel ingots were smelted using a dual process of vacuum induction and vacuum consumables, followed by a peeling process. The alloy composition of the martensitic aging steel ingot is as follows: Co: 11.96%, Ni: 18.18%, Mo: 4.46%, Ti: 1.39%, Al: 0.14%, with the balance being Fe and unavoidable impurities. The contents of key impurity elements are: C: 0.0027%, Si: 0.014%, Mn: 0.012%, P: 0.0013%, S: 0.0016%, N: 0.0005%, O: 0.0006%.

[0053] Step 2: High-temperature homogenization The martensitic aging steel ingots that have undergone peeling are placed in a furnace at a temperature of 1000℃ for high-temperature homogenization. The homogenization conditions include: a holding temperature of 1280℃ and a holding time of 36 hours. After the holding time, the ingots are removed from the furnace and cooled to a forging temperature of 1200℃ before forging.

[0054] Step 3: Forging and blanking The forging process employs a "three-upset, three-drawing" method. The initial forging temperature is 1200℃. The first upset has a reduction of 60% and a drawout rate of 300%. The second upset has a reduction of 55% and a drawout rate of 250%. The third upset has a reduction of 50% and a drawout rate of 200%. The resulting billet is a slab with a length, width, and height of 3000, 1000, and 500 mm, respectively.

[0055] Step 4: Thermal Deformation The slab forgings obtained after the above-mentioned "three upsetting and three drawing" process are reheated in the furnace to 1150℃ and held for 2 hours. Then, they are rolled out of the furnace with a reduction of 20% in the first rolling pass and 10% in subsequent rolling passes, finally obtaining a 20mm thick plate at a final rolling temperature of 950℃.

[0056] Step 5: Heat Treatment The heat treatment process is as follows: hold at 850℃ for 2 hours, then immediately oil cool to room temperature; hold at 820℃ for 1 hour, then immediately oil cool to room temperature, repeat twice; place in a -73℃ cryogenic device for 2 hours within 4 hours, then remove from the cryogenic device and allow to warm up naturally in the air; aging the material after it has warmed up to room temperature within 8 hours, with an aging temperature of 510℃ and a time of 3 hours.

[0057] The mechanical properties of the martensitic aged steels obtained in Examples 1-2 and Comparative Examples 1-2 after aging were tested, and the test results are shown in Table 1.

[0058] Table 1. Mechanical properties of the martensitic aging steels obtained in Examples 1-2 and Comparative Examples 1-2

[0059] Comparative Examples 1 and 2 lack the core alloy design of this application (the contents of Co, Mo, Al, and Mn are all lower than those of this application, and there is no Zr), resulting in insufficient precipitation strengthening effect, tensile strength below 2650 MPa, and yield strength below 2400 MPa.

[0060] In summary, the maraging ultra-high strength steel and its preparation method provided by this invention can yield a novel maraging ultra-high strength steel with a strength Rm≥2650MPa, Rp0.2≥2400MPa, and elongation A>6.0%. Furthermore, the preparation process is relatively simple, eliminating the need for the cold rolling process required by existing technologies, which greatly improves the stability of industrial production (high-alloy ultra-high strength steel is difficult to process at room temperature; eliminating the cold rolling process significantly reduces the risk of cold rolling cracking and facilitates industrial production), thus increasing the product yield. Simultaneously, this invention does not impose strict limitations on the final shape and dimensions of the maraging steel product, allowing its use in a wide range of fields and service scenarios.

[0061] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A high-strength-high-toughness synergistically optimized martensitic aging steel, characterized in that, By mass percentage, it includes: Co: 15.5~17.0%, Ni: 17.0~19.0%, Mo: 6.0~8.0%, Ti: 1.0~2.0%, Al: 0.5~1.0%, Mn: 0.1~0.5%, Zr: 0.01~0.05%, with the balance being Fe and unavoidable impurities.

2. The martensitic aging steel according to claim 1, characterized in that, The martensitic aging steel has a grain size ≥ 8.0, tensile strength ≥ 2650 MPa, yield strength ≥ 2400 MPa, and elongation > 6%.

3. The martensitic aging steel according to claim 1, characterized in that, The impurity element content in the martensitic aging steel, by mass percentage, is: C≤0.008%, Si≤0.1%, P≤0.005%, S≤0.005%, N≤0.0015%, O≤0.0015%.

4. A method for preparing martensitic aging steel as described in any one of claims 1-3, characterized in that, include: The process involves smelting, homogenization, forging, hot deformation, and heat treatment to obtain the martensitic aging steel.

5. The preparation method according to claim 4, characterized in that, The smelting process includes: using a combination of vacuum induction and vacuum self-consumption processes to smelt martensitic aging steel ingots.

6. The preparation method according to claim 4, characterized in that, The homogenization process includes: maintaining a temperature of 1250~1260℃ for 36~60 hours.

7. The preparation method according to claim 4, characterized in that, The forging process includes: multiple upsetting and drawing operations; wherein the initial forging temperature is 1180~1200℃, and the final forging temperature is ≥1000℃; the reduction in each upsetting operation is ≥50%, and the drawing rate in each drawing operation is ≥200%; when the temperature is below 1050℃, the furnace is returned to the furnace and heated at 1100~1200℃ for 1~3 hours before continuing upsetting; when the temperature is below 1000℃, the furnace is returned to the furnace and heated at 1050~1150℃ for 1~3 hours before continuing drawing.

8. The preparation method according to claim 4, characterized in that, The hot deformation includes: reheating the forged material after forging to 1100~1200℃ and holding it at that temperature for 1~3 hours, and then precision forging or rolling it to the target size; wherein the single-pass reduction of precision forging or rolling is ≤35%, and the final forging or final rolling temperature is ≥950℃.

9. The preparation method according to claim 4, characterized in that, The heat treatment includes: Hold at 850~860℃ for 1~2 hours, then cool to room temperature with oil; Hold at 820~830℃ for 1~1.5 hours, then cool to room temperature, and repeat at least once; Place it in a cryogenic device at -70~-80℃ for 1~2 hours to cool, and then allow it to warm up naturally in the air; Materials that have been brought back to room temperature are subjected to aging treatment at a temperature of 480-500℃ for 5-8 hours.

10. The preparation method according to claim 9, characterized in that, The material cooled to room temperature by oil is placed in the cryogenic device for cooling within 4 hours; the material warmed back to room temperature is then subjected to the aging treatment within 8 hours.

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