Aviation gear steel based on surface fine grain treatment and preparation method and application thereof

Abstract

The invention discloses aviation gear steel based on surface fine grain treatment and a preparation method and application thereof. The preparation method of the aviation gear steel based on surface fine grain treatment comprises the following steps: quenching and tempering the aviation gear steel to obtain a tempered sorbite matrix; the surface of the tempered sorbite matrix is subjected to ultrasonic shot blasting treatment, and a surface-modified sample is obtained; and performing gas nitriding treatment on the sample subjected to surface modification to obtain the aviation gear steel based on surface fine grain treatment. According to the method for improving precipitation of the spherical nitride of the aviation gear steel through surface fine grain pretreatment, generation of the nanoscale spherical nitride is efficiently promoted in the gas nitriding process, harm of brittleness of the nitride is avoided, the surface toughness of the aviation gear steel is improved, and the service life of the aviation gear steel is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of composite modification technology of severe plastic deformation and chemical heat treatment on the surface of metallic materials, and particularly relates to an aerospace gear steel based on surface fine grain treatment, its preparation method and application. Background Technology

[0002] Gas nitriding is a primary method of chemical wetting and diffusion on the surface of metallic materials, widely used in the surface strengthening of 18Cr2Ni4W high-strength alloy steel components such as gears and drive shafts for aero-engines. During nitriding, active nitrogen atoms penetrate the steel surface and diffuse inwards, combining with alloying elements such as chromium in the matrix to form nitrides, resulting in significant dispersion strengthening and solid solution strengthening effects. Compared to traditional carburizing or induction hardening processes, gas nitriding offers advantages such as lower processing temperature, less deformation, extremely high surface hardness, and excellent wear resistance and fatigue resistance. It has been proven that gas nitriding can significantly alter the surface microstructure of metals such as 18Cr2Ni4W steel, forming dispersed alloy nitrides. These nitrides modify the metal surface through second-phase particle strengthening and solid solution strengthening, significantly improving its surface strength and hardness. However, while its strength and hardness are improved, the tempered sorbite matrix of 18Cr2Ni4W steel contains a large amount of strong nitride-forming elements such as chromium. Nitrogen atoms are very likely to segregate and grow along the ferrite grain boundaries, forming coarse vein-like or network-like nitrides, resulting in the formation of "nitride brittleness" in the diffusion layer. The toughness of the metal surface is significantly reduced, which is not conducive to the long service life of aircraft gears and drive shafts under high-speed and heavy-load environments.

[0003] The introduction of intense surface plastic deformation (such as ultrasonic shot peening) can achieve significant refinement and nanostructuring of the surface microstructure. This fine-grained surface structure plays a crucial regulatory role in subsequent chemical heat treatment. The refined nano / submicron grains introduce a massive number of grain boundaries. These high-density grain boundaries not only provide rapid diffusion channels for nitrogen atoms but, more importantly, provide dispersed nucleation sites, greatly dispersing nitride precipitation and preventing its enrichment at coarse protoferrite grain boundaries. Simultaneously, the volume confinement effect of the fine-grained structure restricts the long-range directional growth of nitrides, forcing them to tend towards spherical precipitation to reduce surface energy. However, in practical engineering applications, how to transform this theoretical advantage of fine grains into actual nanoscale spherical nitride structures through specific process parameter matching, thereby completely solving the nitride brittleness problem while achieving high hardness, is a pressing technical challenge in the field of surface strengthening of aerospace gears and drive shafts. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the primary objective of this invention is to provide a method for preparing aerospace gear steel based on surface fine grain treatment.

[0005] Another object of the present invention is to provide an aerospace gear steel based on surface fine grain treatment, which is prepared by the above-mentioned method for preparing aerospace gear steel based on surface fine grain treatment.

[0006] Another object of the present invention is to provide the application of the above-mentioned aerospace gear steel based on surface fine grain treatment in the manufacture of aero-engine gears and drive shafts.

[0007] The objective of this invention is achieved through the following technical solution: A method for preparing aerospace gear steel based on surface fine grain treatment includes the following steps: S1. Tempering and heat treatment is performed on aerospace gear steel to obtain a tempered sorbite matrix; S2. The surface of the tempered sorbite matrix described in S1 is subjected to ultrasonic shot peening to obtain a surface-modified sample. The working parameters of the ultrasonic shot peening include: ultrasonic frequency of 15~20kHz, amplitude of 30~50μm, processing distance of 8.5~10mm, feed speed of 15~20m / s, and shot peening time of 2~10min. S3. Perform gas nitriding treatment on the surface-modified sample described in S2 to obtain aerospace gear steel based on surface fine grain treatment.

[0008] Preferably, the specific steps for quenching and tempering the aerospace gear steel in step S1 are as follows: the sample is heated to 850~870℃ and held for 150~180min, then oil-quenched, then heated to 505~525℃ and held for 180~210min for high-temperature tempering, and then air-cooled to obtain a uniform tempered sorbite matrix.

[0009] Preferably, the specific steps for quenching and tempering the aerospace gear steel in step S1 are as follows: the sample is heated to 860~870℃ and held for 150~180min, then oil-quenched, then heated to 515~525℃ and held for 180~210min for high-temperature tempering, and then air-cooled to obtain a uniform tempered sorbite matrix.

[0010] Preferably, the aerospace gear steel in step S1 is 18Cr2Ni4W alloy steel.

[0011] Preferably, the working parameters of the ultrasonic shot peening process in step S2 further include: using a cemented carbide ball with a diameter of 3~4mm as the shot peening medium.

[0012] Preferably, the shot peening time is 8-10 minutes.

[0013] Preferably, the specific steps for gas nitriding treatment of the surface-modified sample in step S3 are as follows: the sample is placed in a nitriding furnace and gas nitrided at a temperature of 480~540℃ for 15~70h, during which the ammonia decomposition rate is controlled at 20~50%.

[0014] Preferably, in the gas nitriding treatment, gas nitriding is carried out at a temperature of 480~490℃ for 40~70h.

[0015] Preferably, in the gas nitriding treatment, the ammonia decomposition rate is controlled to be 35-50%.

[0016] An aerospace gear steel based on surface fine grain treatment is prepared by the above-mentioned preparation method of aerospace gear steel based on surface fine grain treatment.

[0017] The above-mentioned aerospace gear steel based on surface fine grain treatment is used in the manufacture of aero-engine gears and drive shafts.

[0018] Compared with the prior art, the beneficial effects of the present invention include: Traditional gas nitriding processes for 18Cr2Ni4W aerospace gear steel often result in the precipitation of coarse vein-like or network-like nitrides along ferrite grain boundaries, leading to significant problems such as high brittleness and poor fatigue performance of the nitrided layer. This invention provides a method for improving the precipitation of spherical nitrides in aerospace gear steel through surface fine-grain pretreatment. This method efficiently promotes the formation of nanoscale spherical nitrides during gas nitriding, avoiding the harmful effects of nitride brittleness and improving surface toughness and service life. By utilizing the surface nano-sizing effect and high-density crystal defects introduced by ultrasonic shot peening, as well as the diffusion restriction effect of low-temperature nitriding, nitrogen atoms preferentially nucleate in a dispersed manner based on intragranular defects during nitriding, maintaining nanoscale spherical characteristics. Furthermore, through STEM and feedback from the microscopic precipitate morphology, the optimal pretreatment time parameters are selected to both induce a large amount of spherical nitride precipitation and ensure surface integrity, establishing a link between the macroscopic ultrasonic shot peening process and the microscopic precipitate state of the gear steel. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process for preparing aerospace gear steel based on surface fine grain treatment as described in Embodiment 1 of the present invention.

[0020] Figure 2 The surface microstructure of the aerospace gear steel prepared for Comparative Example 1: (a) SEM image, (b) N element distribution map, (c) Cr element distribution map, (d) Fe element distribution map.

[0021] Figure 3The surface microstructure of the aerospace gear steel prepared for Example 1 based on surface fine grain treatment: (a) SEM image, (b) N element distribution map, (c) Cr element distribution map, (d) Fe element distribution map.

[0022] Figure 4 shows the surface HAADF-STEM images of the aerospace gear steel prepared in Example 1 based on surface fine grain treatment: (a) HAADF image, (b) histogram of nitride grain size frequency distribution.

[0023] Figure 5 Surface element distribution diagrams of the aerospace gear steel prepared for Example 1 based on surface fine grain treatment: (a) N element distribution diagram, (b) Cr element distribution diagram, (c) Fe element distribution diagram. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] 18Cr2Ni4W high-strength alloy steel is widely used in the manufacture of key transmission components such as gears and drive shafts for aero-engines due to its excellent comprehensive mechanical properties. To cope with the harsh operating conditions of high speed, heavy load, and long service life, these components typically require surface strengthening treatment. Gas nitriding, as a mature chemical heat treatment process, has become one of the preferred solutions for surface strengthening of such components due to its low processing temperature, minimal workpiece deformation, extremely high surface hardness, and excellent wear resistance and fatigue resistance. During nitriding, active nitrogen atoms penetrate into the steel matrix and combine with alloying elements such as chromium to form dispersed alloy nitrides. Through second-phase particle strengthening and solid solution strengthening effects, the strength and hardness of the material surface layer are significantly improved.

[0026] However, traditional single-gas nitriding processes still face significant technical bottlenecks in practical applications. Because the tempered sorbite matrix of 18Cr2Ni4W steel contains a relatively high amount of strong nitride-forming elements such as chromium, under conventional nitriding conditions, nitrogen atoms readily segregate and grow along ferrite grain boundaries, resulting in the formation of coarse vein-like or network-like nitrides in the nitrided layer. This deterioration of the microstructure leads to severe "nitride embrittlement," significantly reducing the surface toughness of the metal. For aerospace gears and drive shafts subjected to complex alternating loads, increased surface brittleness easily induces early fatigue spalling or fracture, severely limiting the service life and reliability of components.

[0027] To address these issues, academia and engineering have begun exploring the introduction of drastic surface plastic deformation (such as ultrasonic shot peening) as a pretreatment method before nitriding. Theoretical studies have shown that drastic plastic deformation can achieve significant refinement, even nanoscale formation, of the surface microstructure. This fine-grained structure not only introduces high-density grain boundaries, providing rapid diffusion channels for nitrogen atoms, but more importantly, it provides a large number of diffusely distributed nucleation sites, which helps to disperse the precipitation of nitrides and prevent them from accumulating at the original coarse grain boundaries. At the same time, the volume confinement effect of the fine-grained structure can limit the long-range directional growth of nitrides, forcing them to tend towards spherical precipitation, thus theoretically possessing the potential to eliminate network nitrides and solve the brittleness problem.

[0028] Although the theoretical path is clear, in current practical engineering applications, how to truly transform this "fine-grain advantage" into actual, stable nanoscale spherical nitride structures by precisely matching the specific process parameters of ultrasonic shot peening and gas nitriding (such as shot peening intensity, coverage, nitriding temperature, time, and atmosphere control) remains a technical challenge that urgently needs to be solved.

[0029] Therefore, the purpose of this invention is to propose a method for improving the precipitation of spherical nitrides in aerospace gear steel through surface fine-grain pretreatment. By combining the high-density defects introduced by severe surface plastic deformation with low-temperature nitriding, the spherical precipitation of nitrides in 18Cr2Ni4W steel during nitriding is promoted, thereby improving the toughness and fatigue life of the nitrided layer and avoiding the formation of coarse network nitrides. By changing the pretreatment time of ultrasonic shot peening and the temperature and time parameters of gas nitriding, the size and distribution characteristics of spherical nitrides in the nitrided layer of gear steel are comprehensively controlled.

[0030] The objective of this invention is achieved through the following technical solution: A method for preparing aerospace gear steel based on surface fine grain treatment includes the following steps: S1. Tempering and heat treatment is performed on aerospace gear steel to obtain a tempered sorbite matrix; S2. The surface of the tempered sorbite matrix described in S1 is subjected to ultrasonic shot peening to obtain a surface-modified sample. The working parameters of the ultrasonic shot peening include: ultrasonic frequency of 15~20kHz, amplitude of 30~50μm, processing distance of 8.5~10mm, feed speed of 15~20m / s, and shot peening time of 2~10min. S3. Perform gas nitriding treatment on the surface-modified sample described in S2 to obtain aerospace gear steel based on surface fine grain treatment.

[0031] This invention introduces ultrasonic shot peening as a key pretreatment step. Nitrogen atoms no longer segregate along the original ferrite grain boundaries, but instead undergo dispersed nucleation based on intragranular defects such as high-density dislocations and nanograin boundaries introduced by ultrasonic shot peening. Due to the numerous and uniformly distributed nucleation sites, and the limitation of low-temperature diffusion, the nitrides exhibit a dispersed, nanoscale spherical structure. Comparison with the microstructure of conventional nitriding (without shot peening pretreatment) verifies the effectiveness of this method in inducing the precipitation of nanoscale spherical nitrides, thereby obtaining a nitrided layer with both high hardness and high toughness.

[0032] Preferably, the specific steps for quenching and tempering the aerospace gear steel in step S1 are as follows: the sample is heated to 850~870℃ and held for 150~180min, then oil-quenched, then heated to 505~525℃ and held for 180~210min for high-temperature tempering, and then air-cooled to obtain a uniform tempered sorbite matrix.

[0033] In some embodiments of the present invention, in the preparation step of the tempered sorbite matrix, it is necessary to first heat to 850~870℃ and hold for 150~180min before oil quenching, and then heat to 505~525℃ and hold for 180~210min for high-temperature tempering followed by air cooling; wherein, the holding time at 850~870℃ can be 150min, 160min, 170min, and 180min, or any value between the above two values. In this way, the sample can be pre-treated for tempering, providing an ideal matrix state for subsequent surface grain refinement and nitriding processes, thereby ensuring the uniformity and bonding strength of the nitrided layer.

[0034] Preferably, the specific steps for quenching and tempering the aerospace gear steel in step S1 are as follows: the sample is heated to 860~870℃ and held for 150~180min, then oil-quenched, then heated to 515~525℃ and held for 180~210min for high-temperature tempering, and then air-cooled to obtain a uniform tempered sorbite matrix.

[0035] Preferably, the aerospace gear steel in step S1 is 18Cr2Ni4W alloy steel.

[0036] In some embodiments of the present invention, the aerospace gear steel in step S1 is 18Cr2Ni4W alloy steel, because it is one of the highest performance-grade and most widely used heavy-duty carburizing gear steels in the aerospace industry.

[0037] Preferably, the working parameters of the ultrasonic shot peening process in step S2 further include: using a cemented carbide ball with a diameter of 3~4mm as the shot peening medium.

[0038] In some embodiments of the present invention, the working parameters of the ultrasonic shot peening process in step S2 further include: using cemented carbide balls with a diameter of 3-4 mm as the shot peening medium. The advantages of cemented carbide balls are: (1) utilizing the high density characteristics of cemented carbide, the shot is given extremely high kinetic energy under ultrasonic vibration, thereby inducing severe plastic deformation on the surface of 18Cr2Ni4W steel, realizing the nano-refinement of surface grains, and providing abundant channels for the rapid diffusion of nitrogen atoms; (2) the synergistic effect of large size (3-4 mm) and high density can build a residual compressive stress field with large depth and high peak value in the subsurface layer of the material, significantly improving the fatigue resistance of the gear; (3) the cemented carbide medium has extremely high hardness and wear resistance, avoiding medium breakage and surface contamination during the shot peening process, ensuring the cleanliness of the substrate surface, and facilitating the acquisition of a nanoscale dispersed nitriding layer with high bonding strength and uniform structure. The embodiment of the present invention uses YG6 cemented carbide balls with a diameter of 4 mm.

[0039] Preferably, the shot peening time is 8-10 minutes.

[0040] In some embodiments of the present invention, the shot peening time is controlled between 2 and 10 minutes. A treatment time of 2 minutes or more can introduce effective plastic deformation and dislocation multiplication into the surface layer; as the time increases, the density of nanocrystals and defects in the surface layer gradually increases, reaching saturation at around 8 minutes, providing the most sufficient dispersed nucleation sites for spherical nitrides; while controlling the time to within 10 minutes ensures sufficient grain refinement and avoids excessive deterioration of surface roughness or microcrack initiation due to prolonged over-peening.

[0041] Preferably, the specific steps for gas nitriding treatment of the surface-modified sample in step S3 are as follows: the sample is placed in a nitriding furnace and gas nitrided at a temperature of 480~540℃ for 15~70h, during which the ammonia decomposition rate is controlled at 20~50%.

[0042] In some embodiments of the present invention, the specific steps of the gas nitriding treatment are as follows: the sample is placed in a nitriding furnace and held at a temperature of 480~540℃ for 15~70h for gas nitriding, during which the ammonia decomposition rate is controlled at 20~50%; for example, the temperature can be 480℃, 490℃, 500℃, 510℃, 520℃, 530℃ and 540℃ and any two of the above values, and the temperature can be held at such a temperature for 15~70h, so that both diffusion depth and precipitation morphology can be taken into account.

[0043] Preferably, in the gas nitriding treatment, gas nitriding is carried out at a temperature of 480~490℃ for 40~70h.

[0044] In some embodiments of the present invention, gas nitriding is performed by holding at a temperature of 480~490°C for 40~70h; furthermore, a low-temperature long-time process of holding at 490°C for 40h is preferred, which aims to limit the excessive growth of nitrides.

[0045] Preferably, in the gas nitriding treatment, the ammonia decomposition rate is controlled to be 35-50%.

[0046] In gas nitriding, the ammonia decomposition rate is the most critical parameter for controlling the nitrogen potential in the furnace atmosphere. Maintaining the ammonia decomposition rate within the specific range of 35-50% offers the following key advantages: This decomposition rate range provides a suitable concentration of active nitrogen atoms, ensuring an effective nitrogen atom penetration rate under medium-temperature conditions of 480-540℃, meeting the requirements for deep nitriding; furthermore, the moderate nitrogen supply rate matches the nanocrystalline matrix formed by ultrasonic shot peening, promoting the uniform dispersion and precipitation of alloy nitrides in thermodynamically stable nanospheres within the crystal, significantly improving the toughness and bonding strength of the nitrided layer.

[0047] An aerospace gear steel based on surface fine grain treatment is prepared by the above-mentioned preparation method of aerospace gear steel based on surface fine grain treatment.

[0048] The above-mentioned aerospace gear steel based on surface fine grain treatment is used in the manufacture of aero-engine gears and drive shafts.

[0049] Example 1 A method for preparing aerospace gear steel based on surface fine grain treatment, the specific steps of which are as follows: S1. First, the 18Cr2Ni4W alloy steel is subjected to quenching and tempering treatment. The specific process is as follows: the sample is heated to 860℃ and held for 150 min, then oil quenched, then heated to 515℃ and held for 190 min for high-temperature tempering and air cooling to obtain a uniform tempered sorbite matrix.

[0050] S2. The surface of the tempered sorbite matrix described in S1 is subjected to ultrasonic shot peening (Per-USP) to obtain a surface-modified sample. The working parameters of the ultrasonic shot peening are as follows: ultrasonic frequency of 20kHz, amplitude of 50μm, processing distance of 8.5mm, feed speed of 15m / s, shot peening time of 8min, and YG6 cemented carbide ball with a diameter of 4mm as shot peening medium.

[0051] S3. Place the surface-modified sample described in S2 into a nitriding furnace and hold it at 490°C for 40 hours for gas nitriding. During this period, control the ammonia decomposition rate to 35%. After the gas nitriding treatment is completed, cool the sample with the furnace to 80°C and then remove it from the furnace for air cooling to obtain aerospace gear steel based on surface fine grain treatment.

[0052] Comparative Example 1 A method for preparing aerospace gear steel, the specific steps of which are as follows: S1. First, the 18Cr2Ni4W alloy steel is subjected to quenching and tempering treatment. The specific process is as follows: the sample is heated to 860℃ and held for 150 min, then oil quenched, then heated to 515℃ and held for 190 min for high-temperature tempering and air cooling to obtain a uniform tempered sorbite matrix.

[0053] S2. Place the tempered sorbite matrix described in S1 into a nitriding furnace and hold it at 490°C for 40 hours for gas nitriding. During this period, control the ammonia decomposition rate to 35%. After the gas nitriding treatment is completed, cool it to 80°C with the furnace and then remove it from the furnace for air cooling to obtain aerospace gear steel based on surface fine grain treatment.

[0054] The surface of the aerospace gear steel sample prepared in Comparative Example 1 was tested by SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive Spectroscopy). The ammonia decomposition rate was controlled at 35% during the nitriding process. After treatment, the depth of the nitrided layer was measured to be 0.426 mm, and the surface hardness was 826 HV. The test results are as follows: Figure 2 As shown. By Figure 2 SEM morphology combined with EDS energy dispersive spectroscopy analysis shows that, without fine grain pretreatment, the precipitates on the surface of the sample in Comparative Example 1 exhibit obvious continuous network and long needle-like characteristics. This is because elements such as Cr in 18Cr2Ni4W steel tend to segregate at the original ferrite grain boundaries, and the diffusion rate of nitrogen atoms along the grain boundaries at 490℃ is much greater than that within the grains, causing nitrides to preferentially grow along the grain boundaries and connect into a network. This coarse network of nitrides is the main reason for the increased brittleness of the diffusion layer, which seriously limits the service performance of gear steel.

[0055] The aerospace gear steel prepared in Example 1 was characterized at the micrometer level, and its surface hardness was measured to be 889 HV, with a penetration layer depth of 0.456 mm. The surface SEM and EDS test results are as follows: Figure 3 As shown, with Figure 2 contrast, Figure 3 The surface morphology of the sample in Example 1 showed a fundamental change. The coarse vein-like or network-like nitrides commonly seen in Comparative Example 1 completely disappeared. EDS surface scanning showed that the distribution of nitrogen and alloying elements was highly uniform, and no obvious grain boundary segregation was observed. This indicates that the 8-minute ultrasonic shot peening treatment effectively introduced intragranular defects, broke up the path of continuous nitride growth along the grain boundaries, and achieved macroscopic microstructure homogenization.

[0056] To further investigate the fine structure of the surface nitrides in the sample prepared in Example 1, HAADF-STEM observation and particle size analysis were performed (test results are shown in Figure 1). Figure 4 As shown), and combined with EDS elemental surface scan ( Figure 5 ) will be analyzed. Figure 4It can be seen that a large number of regular spherical second-phase particles were dispersed in the matrix, and their average particle size was approximately 10 nm and they were evenly distributed. Figure 5 The elemental distribution further confirmed that there was significant enrichment of N and Cr elements in these spherical particles, which were identified as dispersed precipitates of nanoscale alloy nitrides.

[0057] To further investigate the fine structure of nitrides on the surface of the sample from Example 1, HAADF-STEM observation and particle size analysis were performed (e.g., Figure 4 As shown), and combined with EDS element surface scan (such as... Figure 5 Analysis will be performed as shown. (From...) Figure 4 It can be seen that a large number of uniform spherical second phase particles were dispersed in the matrix, and their average particle size was approximately 10 nm and they were uniformly distributed. Figure 5 The elemental distribution further confirms that there is significant enrichment of N and Cr elements in the corresponding regions of these spherical particles, confirming that they are dispersed precipitated nanoscale alloy nitrides.

[0058] comprehensive Figures 2-4 As can be seen, Example 1, by introducing high-density dislocations and nanograin boundaries into the surface layer through ultrasonic shot peening, altered the nucleation kinetics of nitrides, successfully suppressing the intergranular network growth that occurred in Comparative Example 1, and inducing the nitrides to transform into nanoscale spherical dispersed precipitates. These spherical precipitates, while maintaining surface hardness, eliminate the disruptive effect of the network structure, thus verifying the significant effect of the method of this invention in improving the precipitation of spherical nitrides in aerospace gear steel.

[0059] Example 2 Example 2 provides a method for preparing aerospace gear steel based on surface fine grain treatment. Compared with Example 1, the only difference is that the working parameters of the ultrasonic shot peening treatment are: ultrasonic frequency of 20kHz, amplitude of 50μm, processing distance of 8.5mm, feed speed of 15m / s, shot peening time of 10min, and YG6 cemented carbide ball with a diameter of 4mm as shot peening medium.

[0060] Example 3 Example 3 provides a method for preparing aerospace gear steel based on surface fine grain treatment. Compared with Example 1, the only difference is that the working parameters of the ultrasonic shot peening treatment are: ultrasonic frequency of 20kHz, amplitude of 50μm, processing distance of 8.5mm, feed speed of 15m / s, shot peening time of 5min, and YG6 cemented carbide ball with a diameter of 4mm as shot peening medium.

[0061] The aerospace gear steels prepared in Examples 2 and 3 have a similar microstructure to those in Example 1, successfully suppressing the network precipitation of nitrides along grain boundaries and inducing their dispersion in nanoscale spherical morphology.

[0062] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing aerospace gear steel based on surface fine-grain treatment, characterized in that, Includes the following steps: S1. Tempering and heat treatment is performed on aerospace gear steel to obtain a tempered sorbite matrix; S2. The surface of the tempered sorbite matrix described in S1 is subjected to ultrasonic shot peening to obtain a surface-modified sample. The working parameters of the ultrasonic shot peening include: ultrasonic frequency of 15~20kHz, amplitude of 30~50μm, processing distance of 8.5~10mm, feed speed of 15~20m / s, and shot peening time of 2~10min. S3. Perform gas nitriding treatment on the surface-modified sample described in S2 to obtain aerospace gear steel based on surface fine grain treatment.

2. The method for preparing aerospace gear steel based on surface fine-grain treatment according to claim 1, characterized in that, The specific steps for quenching and tempering aerospace gear steel described in step S1 are as follows: the sample is heated to 850~870℃ and held for 150~180min, then oil-quenched, then heated to 505~525℃ and held for 180~210min for high-temperature tempering, and then air-cooled to obtain a uniform tempered sorbite matrix. and / or The aerospace gear steel mentioned in step S1 is 18Cr2Ni4W alloy steel.

3. The method for preparing aerospace gear steel based on surface fine-grain treatment according to claim 2, characterized in that, The specific steps for quenching and tempering the aerospace gear steel described in step S1 are as follows: the sample is heated to 860~870℃ and held for 150~180min, then oil-quenched, then heated to 515~525℃ and held for 180~210min for high-temperature tempering, and then air-cooled to obtain a uniform tempered sorbite matrix.

4. The method for preparing aerospace gear steel based on surface fine-grain treatment according to claim 1, characterized in that, The working parameters for ultrasonic shot peening in step S2 also include: using cemented carbide balls with a diameter of 3-4 mm as the shot peening medium.

5. The method for preparing aerospace gear steel based on surface fine-grain treatment according to claim 4, characterized in that, YG6 cemented carbide balls with a diameter of 4mm were used as the shot peening medium; and / or The shot peening time is 8-10 minutes.

6. The method for preparing aerospace gear steel based on surface fine-grain treatment according to claim 1, characterized in that, The specific steps for gas nitriding treatment of the surface-modified sample described in step S3 are as follows: the sample is placed in a nitriding furnace and kept at 480~540℃ for 15~70h for gas nitriding, during which the ammonia decomposition rate is controlled at 20~50%.

7. The method for preparing aerospace gear steel based on surface fine-grain treatment according to claim 6, characterized in that, In the gas nitriding process, gas nitriding is carried out by maintaining a temperature of 480~490℃ for 40~70h.

8. The method for preparing aerospace gear steel based on surface fine-grain treatment according to claim 6, characterized in that, In the gas nitriding treatment, the ammonia decomposition rate is controlled at 35-50%.

9. An aerospace gear steel based on surface fine-grain treatment, characterized in that, It is prepared by the method for preparing aerospace gear steel based on surface fine grain treatment as described in any one of claims 1 to 8.

10. The application of the aerospace gear steel based on surface fine grain treatment as described in claim 9 in the manufacture of aero-engine gears and drive shafts.

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