A hot working method for effectively improving strength and plasticity of high Co-Ni steel
By combining SPS in-situ forging and hot rolling technologies, the precipitation of nanotwins in high Co-Ni steel is controlled, solving the problem of insufficient strength and plasticity of high Co-Ni steel, and achieving simultaneous improvement of strength and plasticity of high Co-Ni steel, which is suitable for military equipment and other fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YANAN UNIV
- Filing Date
- 2024-01-12
- Publication Date
- 2026-05-19
AI Technical Summary
Existing high-Co-Ni steels have insufficient strength and ductility, making it difficult to further improve strength without reducing ductility, which limits their application in fields such as military equipment.
A high-density nanotwin structure is formed by combining SPS in-situ forging and hot rolling technologies to control the precipitation of nanotwins in high Co-Ni steel. This process includes steps such as high-temperature austenitization, quenching, cryogenic treatment, SPS compression deformation, SPS in-situ forging, high-temperature rolling, and low-temperature annealing.
It significantly improves the strength and plasticity of high Co-Ni steel, increasing tensile strength by approximately 10.4% and elongation after fracture by 10.8%, achieving simultaneous improvement in strength and plasticity. At the same time, it is simple to operate, has low energy consumption, and is suitable for large-scale industrial production.
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Figure CN117867241B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of hot working technology for steel materials, and specifically to a hot working method that effectively improves the strength and plasticity of high Co-Ni steel. Background Technology
[0002] High-Co-Ni steel is a class of metallic structural materials with broad research and application prospects. Due to its ultra-high strength, good plasticity, high fracture toughness, high fatigue strength, and excellent strength-toughness balance, it has been successfully used in key components of major equipment such as aircraft landing gear, high-strength bolts, and rocket and missile casings. Typical examples of high-Co-Ni steel include AerMet100 steel and Ferrium M54, developed by QuesTek in 2013. Based on AerMet100 steel, Ferrium M54 optimizes the alloy element configuration and adds a small amount of W, giving it excellent strength-toughness balance and outstanding resistance to stress corrosion. Furthermore, M54 steel reduces the content of the precious metal Co, resulting in a cost advantage. As a new type of high-Co-Ni steel, M54 shows great application potential and is expected to replace AerMet100 steel in key structural components of large military aircraft, ships, and other military equipment.
[0003] Currently, the preparation and performance optimization technology of high-Co-Ni steel has formed a relatively mature and stable process route. Among these, subsequent heat treatment has a significant effect on improving the steel's properties. High-temperature austenitization dissolves coarse cementite in the steel; quenching and cryogenic treatment are used to obtain a complete lath martensite structure; and aging treatment promotes the dispersed precipitation of fine M2C carbides in high-Co-Ni steel, providing a secondary hardening effect. In short, aging treatment is a very important step in the heat treatment process of high-Co-Ni steel, and a key link in obtaining ultra-high strength and good toughness. In short, the ultra-high strength of high-Co-Ni steel mainly comes from the fine lath martensite matrix and the precipitation strengthening of nano-sized M2C carbides within the matrix. After heat treatment, the tensile strength of M54 steel can reach 2 GPa. Although the main strengthening mechanism of high-Co-Ni steel is generally agreed upon, research on the strengthening and toughening mechanism and methods of high-Co-Ni steel remains a key focus and challenge in the research and design of secondary hardening ultra-high strength steels. With the development of military science and technology, especially the increasing demands on the performance of ultra-high strength steel in the more demanding service environment of high-end military equipment, it is necessary to develop new methods for strengthening and toughening high Co-Ni steel based on existing research, and strive to further improve its strength and broaden its application fields without reducing its plasticity. Summary of the Invention
[0004] The purpose of this invention is to address the problem of insufficient strength and plasticity in high-Co-Ni steel in existing technologies, and to provide an effective hot working method for improving the strength and plasticity of high-Co-Ni steel. This method utilizes a combination of SPS in-situ forging and hot rolling technologies to control the precipitation of nanotwins in high-Co-Ni steel. It is simple to operate, has low energy consumption, and can effectively improve the strength and plasticity of Co-Ni steel.
[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a hot working method for effectively improving the strength and plasticity of high Co-Ni steel, comprising the following steps:
[0006] S1. Heat treatment: The forged high Co-Ni steel is subjected to a heat treatment process of "high temperature austenitization - quenching - deep cryogenic treatment - aging treatment - air cooling" to obtain aged high Co-Ni steel specimens;
[0007] S2, SPS compression deformation: The aged high Co-Ni steel specimen is processed into a specimen with a diameter of Φ1 and a height of h1 by wire cutting. The specimen is cleaned with an ultrasonic cleaner, dried, and then placed in a high-strength carbon fiber mold with an inner diameter of Φ2. The specimen is then subjected to hot compression deformation in an SPS device.
[0008] S3, SPS in-situ forging: After hot compression deformation is completed, the heating rate is adjusted, the temperature is continued to rise to the in-situ forging temperature, the current is turned off, and pressure is continued to be applied to perform SPS in-situ forging treatment to obtain a high Co-Ni steel specimen with a diameter of Φ2.
[0009] S4. High-temperature rolling: The high Co-Ni steel specimen with a diameter of Φ2 is subjected to high-temperature rolling in a two-roll hot rolling mill;
[0010] S5. Low-temperature annealing: The high-Co-Ni steel specimens rolled at high temperature are placed in a vacuum muffle furnace for annealing. After annealing, the specimens are cooled to room temperature with the furnace to obtain high-Co-Ni steel specimens with nanotwin structure reinforcement.
[0011] Preferably, the SPS compression deformation in S2 is as follows: the temperature is increased at a rate of 100℃ / min until it reaches 850℃~950℃. The temperature is kept constant, and pressure is applied at a rate of 30KN / min~50KN / min. The axial pressure is 30MPa~40MPa. The pressure is kept constant, and the temperature and pressure are maintained for 1min~3min.
[0012] Preferably, the SPS in-situ forging in S3 is as follows: the temperature is increased at a rate of 50℃ / min until the in-situ forging temperature reaches 950℃~1000℃, the current is turned off, and the pressure is continued to be applied to 70MPa~80MPa at a rate of 50KN / min~70KN / min. The pressure is kept constant until the specimen cools to below 200℃, then it is removed from the mold to obtain a high Co-Ni steel specimen with a diameter of Φ2.
[0013] Preferably, in S4, the high-temperature rolling is as follows: the high Co-Ni steel specimen obtained in S3 is placed in a vacuum muffle furnace and heated to 1000°C and held for 30 minutes; then, the first rolling pass is performed, with the rolling deformation set at 10%, and so on, for a total of eight rolling passes, with a total rolling deformation of 80%.
[0014] Preferably, the annealing temperature in S5 is 500°C and the annealing time is 1 hour.
[0015] Preferably, 10≤h1≤20mm, 10≤Φ1≤20mm, and 10mm≤Φ2-Φ1≤20mm.
[0016] Preferably, Φ2-Φ1=10mm.
[0017] Further optimization revealed that the dies used for SPS compression deformation and SPS in-situ forging are both high-strength carbon fiber dies.
[0018] Further preferred, the microstructure of the high Co-Ni steel specimen reinforced with nanotwin structure is high dislocation density lath martensite, with high-density nanotwin structure distributed in the martensite matrix.
[0019] More preferably, the high Co-Ni steel specimen reinforced with the nanotwin structure has a tensile strength of 2175 MPa and an elongation after fracture of 13.3%.
[0020] The beneficial effects of this invention are as follows:
[0021] (1) The hot working method of this invention, through the relatively low deformation temperature and short holding time of SPS compression deformation in step S2, can both fully austenitize the steel and effectively control the austenite grain size; the preferred SPS compression deformation operation with an inner diameter difference of 10 mm can ensure the amount of material compression deformation and avoid cracking around the material due to excessive compression deformation, thus preventing the initiation of internal cracks in the specimen; the higher strain rate of SPS compression deformation promotes the formation of nanotwin structures inside the material. Then, through the SPS in-situ forging technology in step S3, the growth rate, density and aspect ratio of twins in the martensitic matrix of high Co-Ni steel are further improved. Therefore, the method in this invention, through the combination of five steps—pre-treatment, SPS high-temperature-high-strain-rate compression deformation, SPS in-situ forging, high-temperature rolling, and low-temperature annealing—can obtain a high-density nanotwin structure in the martensitic matrix of high Co-Ni steel. Furthermore, it can effectively control the generation density and size distribution of the nanotwin structure, thereby significantly improving the strength and plasticity of high Co-Ni steel and breaking through the strength-plasticity combination level of Co-Ni steel.
[0022] (2) The high-Co-Ni steel with high density nanotwin structure reinforced by the present invention has increased tensile strength by about 10.4% and elongation after fracture by 10.8% without reducing elongation. The martensitic matrix contains a high-density nanotwin structure. The nanotwins are arranged in parallel as slender strips in the martensitic matrix. The width of the martensitic strips is 100-300 nm, which realizes the simultaneous improvement of strength and plasticity of Co-Ni steel.
[0023] (3) The method in this invention is simple to operate, has low energy consumption and low production cost, and is suitable for large-scale industrial production applications. Attached Figure Description
[0024] Figure 1 (a) is an OM image of the microstructure of the high-Co-Ni steel specimen reinforced with high-density nanotwin structure prepared in Example 1; (b) is a TEM dark-field image of the high-Co-Ni steel specimen prepared in Example 1 with high-density nanotwin structure.
[0025] Figure 2 The microstructure of the high-Co-Ni steel reinforced with high-density nanotwin structure prepared in Example 1 is shown in the SEM image (a) and the TEM bright-field image of lath martensite (b).
[0026] Figure 3 The diagram shows the engineering stress-engineering strain curve of the high-Co-Ni steel reinforced with high-density nanostructure prepared in Example 1. Detailed Implementation
[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.
[0028] In the following embodiments: Ferrium M54 raw material is cast bar stock with a diameter of 170mm, provided by Beijing Iron and Steel Research Institute. Ferrium M54 is a high-Co-Ni secondary hardening ultra-high strength steel.
[0029] The SPS sintering system is model Dr.Sinter:Model SPS-3.20MK-IV.
[0030] The room temperature tensile mechanical property test was strictly carried out in accordance with the provisions of GB / T 228-2002 "Metallic Materials - Tensile Testing at Room Temperature" and was conducted on a universal testing machine (INSTRON 5985). The parallel section size of the specimen used for tensile testing was 12mm × 3mm × 2mm.
[0031] The carbon fiber mold was provided by Beijing Tianhai High Carbon Fiber Materials Technology Co., Ltd.
[0032] Microscopic tissue observation was performed using a metallurgical microscope, specifically an Olympus PME-3.
[0033] The field emission scanning electron microscope (SEM) model is Hitachi S-4800N.
[0034] Example 1
[0035] (1) Heat treatment: The Φ170 cast high Co-Ni steel bar was machined into Φ15*200 round bar specimens by wire cutting and then subjected to heat treatment. The specific heat treatment process is as follows:
[0036] The specific heat treatment process is as follows: The Φ15*200 round bar specimen is placed in a cylindrical box furnace, heated at a rate of 10℃ / min, heated to 1060℃, held for 1.5h, removed, and placed in a vacuum quenching furnace for oil quenching to room temperature; removed and immediately transferred to a -73℃ cryogenic treatment chamber for cryogenic treatment for 2h; removed and allowed to recover to room temperature in air; then heated to 515℃ in a cylindrical box furnace at a rate of 5℃ / min, held for 10h, removed and cooled to room temperature in air.
[0037] (2) SPS compression deformation: The specimen obtained in step (1) is processed into a cylindrical specimen with a diameter of Φ1=15mm and a height of h1=12mm by wire cutting. It is cleaned with an ultrasonic cleaner, dried with a hair dryer, and then placed in the center of a high-strength carbon fiber mold with an inner diameter of Φ2=25mm. SPS high temperature-high strain rate compression deformation is carried out in the SPS equipment.
[0038] The specific SPS compression deformation process is as follows: the temperature is increased at a rate of 100℃ / min until it reaches 900℃. The temperature is kept constant, and pressure is applied at a rate of 30KN / min with an axial pressure of 30MPa. The pressure is kept constant, and the temperature and pressure are maintained for 1 minute. At this point, the SPS hot compression deformation is complete.
[0039] (3) SPS in-situ forging: After step (2) is completed, adjust the heating rate, heat up to the in-situ forging temperature, turn off the current, continue to apply pressure, and perform SPS in-situ forging.
[0040] The specific SPS in-situ forging process is as follows: After step (2), adjust the heating rate to 50℃ / min, raise the temperature to the in-situ forging temperature of 1000℃, turn off the sintering current, continue to apply pressure to 70MPa at a pressure loading rate of 50KN / min, keep the pressure constant, and wait for the specimen to cool to below 200℃ before unloading the pressure. The SPS in-situ forging is then completed. Remove the specimen from the mold to obtain a high Co-Ni steel cylindrical specimen with a diameter of Φ2=25mm and a height of h2=4.32mm obtained by SPS forging.
[0041] (4) High-temperature rolling: After step (3) is completed, the specimen with a diameter of Φ2=25mm and a height of h2=4.32mm is hot rolled in a two-roll hot rolling mill.
[0042] The specific rolling process parameters are as follows: First, the specimen is placed in a vacuum muffle furnace and heated to 1000℃, held for 30 minutes, and then the first rolling pass is performed with a rolling amount of 10%; this process is repeated for a total of eight rolling passes, with a total rolling deformation of 80%, and the thickness of the specimen after rolling is d = 1.12 mm.
[0043] (5) Low-temperature annealing: The high Co-Ni steel specimen with a thickness of d = 1.12 mm obtained in step (4) is subjected to annealing treatment.
[0044] The specific annealing process parameters are as follows: annealing temperature is 500℃, annealing time is 1h, and after annealing, the specimen is cooled to room temperature in the furnace to obtain a high-Co-Ni steel specimen with high-density twin structure reinforcement.
[0045] The high-Co-Ni steel specimen reinforced with a high-density nanotwin structure prepared in Example 1 was subjected to microstructure observation and mechanical property testing. The test results are as follows:
[0046] 1. The high-density nanotwinned high-Co-Ni steel prepared in Example 1 exhibits a high-density nanotwinned structure dispersed in martensitic laths. The nanotwins are arranged in parallel within the martensitic matrix. The results are shown in [Figure 1]. Figure 1 .
[0047] 2. The high-Co-Ni steel reinforced with a high-density nanotwin structure prepared in Example 1 has a microstructure of fine lath martensite with high dislocation density, and the laths are small in size, with a lath width of approximately 100–200 nm; the results are shown in […]. Figure 2 Therefore, it can be seen that the microstructure of high Co-Ni steel after SPS high temperature-high strain rate compression deformation, SPS in-situ forging, high temperature rolling and low temperature annealing is high dislocation density lath martensite with no grain growth tendency and high density nanotwin structure arranged in parallel on the martensite matrix.
[0048] 3. The high-Co-Ni steel reinforced with a high-density nanotwin structure obtained in Example 1 was subjected to room-temperature tensile mechanical property tests using a universal testing machine (INSTRON 5985). The test results showed that its tensile strength was 2175 MPa and its elongation after fracture was 13.3%. The test results were plotted as stress-strain curves, see [see figure]. Figure 3 The test results show that the high-cobalt-cobalt steel with high-density nanotwin structure reinforced by Example 1 has a tensile strength that is about 10.4% higher than that before the process of this invention; at the same time, its elongation is increased by 10.8%, achieving a synergistic improvement in the strength and plasticity of high-cobalt-cobalt steel.
[0049] Example 2
[0050] (1) Same as Example 1.
[0051] (2) SPS high temperature-high strain rate compression deformation: The specimen obtained in step (1) is processed into a cylindrical specimen with a diameter of Φ1=15mm and a height of h1=12mm by wire cutting. It is cleaned with an ultrasonic cleaner, dried with a hair dryer, and then placed in the center of a high-strength carbon fiber mold with an inner diameter of Φ2=25mm. It is then subjected to hot compression deformation in an SPS device.
[0052] The specific SPS compression deformation process is as follows: the temperature is increased at a rate of 100℃ / min until it reaches 950℃. The temperature is kept constant, and pressure is applied at a rate of 40KN / min with an axial pressure of 40MPa. The pressure is kept constant, and the temperature and pressure are maintained for 3 minutes. At this point, the SPS compression deformation is complete.
[0053] (3) SPS in-situ forging: After step (2) is completed, adjust the heating rate, heat up to the in-situ forging temperature, turn off the current, continue to apply pressure, and keep the pressure unchanged to carry out SPS in-situ forging.
[0054] The specific SPS in-situ forging process is as follows: After step (2), adjust the heating rate to 50℃ / min, and heat to the in-situ forging temperature of 1000℃. Turn off the sintering current and continue to apply pressure to 80MPa at a rate of 70KN / min. Keep the pressure constant until the specimen cools to below 200℃, then unload the pressure. The SPS in-situ forging is complete. Remove the specimen from the mold and obtain a high-density nanotwinned structure reinforced high-Co-Ni steel specimen with a diameter of Φ2=25mm and a height of h2=4.32mm obtained by SPS forging.
[0055] (4) Same as Example 1.
[0056] (5) In the same manner as in Example 1, a high-density nanotwin structure reinforced high-Co-Ni steel specimen was prepared.
[0057] The high-density nanotwinned structure reinforced high-Co-Ni steel specimen prepared in Example 2 was subjected to room temperature mechanical property testing using a universal testing machine. The test results are as follows:
[0058] The high-Co-Ni steel specimen reinforced with a high-density nanotwin structure prepared in Example 2 was subjected to room temperature tensile mechanical property tests using a universal testing machine (INSTRON 5985). The test results showed that its tensile strength was 2168 MPa and its elongation after fracture was 12.5%. The test results indicate that the high-Co-Ni steel reinforced with a high-density nanotwin structure prepared in Example 2 exhibited an increase in tensile strength of approximately 10.1% and an increase in elongation of 4.2%, achieving a simultaneous improvement in both strength and plasticity of the high-Co-Ni steel.
[0059] The specification and drawings of this invention are intended to be illustrative rather than restrictive. Based on this invention, those skilled in the art can make substitutions and modifications to some of the technical features without creative effort, and all such modifications are within the scope of protection of this invention.
Claims
1. A hot working method for effectively improving the strength and plasticity of high Co-Ni steel, characterized in that, Includes the following steps: S1. Heat treatment: The forged high Co-Ni steel is subjected to a heat treatment process of "high temperature austenitization - quenching - deep cryogenic treatment - aging treatment - air cooling" to obtain aged high Co-Ni steel specimens; S2, SPS compression deformation: The aged high Co-Ni steel specimen was machined into a specimen with a diameter of Φ1 and a height of h1 by wire cutting. The specimen was cleaned with an ultrasonic cleaner, dried, and then placed in a high-strength carbon fiber mold with an inner diameter of Φ2. The specimen was subjected to high temperature-high strain rate compression deformation in the SPS equipment. S3, SPS in-situ forging: After SPS compression deformation is completed, the heating rate is adjusted, the temperature is continued to rise to the in-situ forging temperature, the current is turned off, and pressure is continued to be applied to perform SPS in-situ forging treatment to obtain a high Co-Ni steel specimen with a diameter of Φ2. S4. High-temperature rolling: The high-Co-Ni steel specimen with a diameter of Φ2 obtained in S3 was placed in a vacuum muffle furnace and heated to 1000℃, and held for 30 min; then, it was rolled in a two-roll hot rolling mill in the first high-temperature pass, with a rolling deformation of 10%, and so on, for a total of eight passes, with a total rolling deformation of 80%; S5. Low-temperature annealing: The high-Co-Ni steel specimens rolled at high temperature were placed in a vacuum muffle furnace for annealing. The annealing temperature for low-temperature annealing was 500℃ and the annealing time was 1h. After annealing, the specimens were cooled to room temperature with the furnace to obtain high-Co-Ni steel specimens with nanotwin structure reinforcement.
2. The method according to claim 1, characterized in that, The SPS compression deformation in S2 is as follows: the temperature is increased at a rate of 100℃ / min until it reaches 850℃~950℃. The temperature is kept constant, and pressure is applied at a rate of 30KN / min~50KN / min. The axial pressure is 30MPa~40MPa. The pressure is kept constant, and the temperature and pressure are maintained for 1min~3min.
3. The method according to claim 1, characterized in that, The SPS in-situ forging in S3 is as follows: the temperature is increased at a rate of 50℃ / min until the in-situ forging temperature reaches 950℃~1000℃. The current is then turned off, and the pressure is continued to be applied to 70MPa~80MPa at a rate of 50KN / min~70KN / min. The pressure is kept constant until the specimen cools to below 200℃. The specimen is then removed from the mold to obtain a high Co-Ni steel specimen with a diameter of Φ2.
4. The method according to claim 1, characterized in that, 10≤h1≤20mm, 10≤Φ1≤20mm, 10mm≤Φ2-Φ1≤20mm.
5. The method according to claim 4, characterized in that, Φ2-Φ1=10mm.
6. The method according to claim 1, characterized in that, The dies used for SPS compression deformation and SPS in-situ forging are all high-strength carbon fiber dies.
7. The method according to claim 1, characterized in that, The microstructure of the high Co-Ni steel specimen reinforced with nanotwin structure is high dislocation density lath martensite, with high-density nanotwin structure distributed in the martensite matrix.
8. The method according to claim 1, characterized in that, The high-Co-Ni steel specimen reinforced with the nanotwin structure has a tensile strength of 2175 MPa and an elongation after fracture of 13.3%.