An additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution
By optimizing the process parameters of 8Cr4Mo4V steel powder with bimodal particle size distribution and laser powder bed melting, the problems of insufficient density and surface quality of powder with unimodal particle size distribution were solved, and 8Cr4Mo4V steel components with high density and low roughness were realized, which are suitable for the manufacture of high-performance complex components for aero-engines.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2026-05-11
- Publication Date
- 2026-06-30
AI Technical Summary
In existing laser powder bed fusion forming processes, the unimodal particle size distribution of 8Cr4Mo4V steel powder results in insufficient density and surface quality of the formed components, making it difficult to meet the manufacturing requirements of high-performance complex components for aero-engines.
By using 8Cr4Mo4V steel powder with a bimodal particle size distribution, and adjusting the mass ratio of fine powder to coarse powder to 2:8~3:7, combined with the optimization of laser powder bed melting process parameters, the powder bed is tightly packed and the laser energy is absorbed efficiently, thus preparing 8Cr4Mo4V steel components with high density and low surface roughness.
It achieves high density (up to 98.94%) and low surface roughness (down to 2.031μm) for 8Cr4Mo4V steel components, broadens the forming process window, and meets the manufacturing requirements of aero-engines for high-performance complex components.
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Figure CN122299016A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metal material preparation technology, specifically relating to an additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size powder ratio. Background Technology
[0002] 8Cr4Mo4V steel is a high-temperature bearing steel specifically designed for aero-engines. It is widely used in bearing manufacturing under high-speed, high-temperature, and high-load conditions and is an irreplaceable core material for aero-engine main shaft bearings. However, traditional bearing forming methods suffer from problems such as low material utilization, long production cycles, and difficulty in forming complex structures, making it difficult to meet the forming and integration requirements of next-generation engines for reduced energy consumption, thin walls, irregular shapes, and integrated construction.
[0003] Laser Powder Bed Fusion (LPBF), a commonly used metal additive manufacturing technology, achieves rapid prototyping by melting metal powder layer by layer with a focused laser beam. It boasts a short preparation cycle, the advantage of integrated forming, and can significantly improve the integration and production efficiency of components. This provides a new technological approach for the manufacturing of complex and precision components made of 8Cr4Mo4V steel.
[0004] In laser powder bed melting (LBD) processes, powder bed packing density is a crucial factor affecting the density and surface quality of the formed components. Higher powder bed packing density reduces interlayer voids and improves molten pool stability, resulting in high-density components with low surface roughness. Current technologies typically employ unimodal metal powders for LBD, with a narrow particle size distribution, mostly ranging from 15 to 53 μm. Studies have shown that, compared to unimodal powders with a relatively uniform particle size distribution, bimodal powders allow smaller particles to effectively fill the gaps between larger particles, mitigating the lower packing density of unimodal powders and thus improving the quality and performance of the formed components. Currently, research on LBD process parameters mainly focuses on unimodal powders with a particle size distribution of 15–53 μm, while bimodal powder systems comprise two significantly different particle size groups, exhibiting significant differences in laser absorptivity and molten pool flowability. Therefore, there is an urgent need to develop an additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution powder ratio, and to match and optimize the laser powder bed melting process parameters suitable for powders with bimodal particle size distribution, so as to achieve precision forming of high-density, high-surface-quality 8Cr4Mo4V steel components to meet the manufacturing needs of high-performance complex components in the aerospace field. Summary of the Invention
[0005] The purpose of this invention is to address the problem that the density of products manufactured using laser powder bed melting forming process with metal powders having a single-peak distribution needs to be improved, and to provide an additive manufacturing method for 8Cr4Mo4V steel based on a bimodal particle size powder ratio.
[0006] The additive manufacturing method of 8Cr4Mo4V steel based on bimodal particle size powder ratio of the present invention is implemented according to the following steps:
[0007] 1. 8Cr4Mo4V bearing steel bars are heated and melted in a vacuum environment to obtain molten metal liquid. The molten metal liquid is then used to prepare metal powder by gas atomization powder preparation method. The metal powder is sieved to obtain fine powder with a particle size of 0.1~15μm and coarse powder with a particle size of 38~60μm. The fine powder and coarse powder are mixed evenly at a mass ratio of 2:8~3:7. After vacuum drying, 8Cr4Mo4V steel powder with a bimodal particle size distribution is obtained.
[0008] 2. Using 8Cr4Mo4V steel powder with a bimodal particle size distribution as raw material, a laser powder bed melting forming process is adopted. The laser power is controlled at 240~300W, the scanning speed is 600~1200mm / s, the substrate preheating temperature is 150~200℃, and the scanning strategy is strip scanning to form 8Cr4Mo4V steel components.
[0009] Compared with existing technologies, the additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size powder ratio of the present invention has the following advantages:
[0010] 1) This invention optimizes the design of the fine and coarse powder ratio to achieve close packing of the powder bed, reduce interlayer voids, and improve the stability of the molten pool. At the same time, it matches and optimizes process parameters to obtain a wider forming process window for 8Cr4Mo4V steel components.
[0011] 2) The present invention uses some fine powder with smaller particle size, which increases the specific surface area of the powder and has a high laser absorption rate. During the melting process, it can quickly form a continuous liquid film, reduce the surface tension of the molten pool, thereby reducing the tendency to spheroidize and improving the surface quality of the formed component.
[0012] 3) This invention optimizes the laser powder bed melting process parameters for 8Cr4Mo4V steel powder with a bimodal particle size distribution to obtain 8Cr4Mo4V steel components with dense structure and excellent performance.
[0013] In summary, this invention achieves the preparation of 8Cr4Mo4V steel components with a maximum density of 98.94% and a minimum roughness of 2.031μm by controlling the ratio of fine to coarse powders, constructing an optimal bimodal particle size distribution system, increasing the powder bed packing density, improving the laser energy absorption rate, and matching and optimizing the laser powder bed melting process parameters. Attached Figure Description
[0014] Figure 1 This is a particle size distribution diagram of 8Cr4Mo4V steel powder with a fine to coarse powder ratio of 3:7 and a bimodal particle size distribution prepared in Example 2.
[0015] Figure 2 The image shows the SEM morphology of 8Cr4Mo4V steel powder with a fine to coarse powder ratio of 3:7 and a bimodal particle size distribution prepared in Example 2. Detailed Implementation
[0016] Specific Implementation Method 1: This implementation method for additive manufacturing of 8Cr4Mo4V steel with bimodal particle size distribution is carried out according to the following steps:
[0017] 1. 8Cr4Mo4V bearing steel bars are heated and melted in a vacuum environment to obtain molten metal liquid. The molten metal liquid is then used to prepare metal powder by gas atomization powder preparation method. The metal powder is sieved to obtain fine powder with a particle size of 0.1~15μm and coarse powder with a particle size of 38~60μm. The fine powder and coarse powder are mixed evenly at a mass ratio of 2:8~3:7. After vacuum drying, 8Cr4Mo4V steel powder with a bimodal particle size distribution is obtained.
[0018] 2. Using 8Cr4Mo4V steel powder with a bimodal particle size distribution as raw material, a laser powder bed melting forming process is adopted. The laser power is controlled at 240~300W, the scanning speed is 600~1200mm / s, the substrate preheating temperature is 150~200℃, and the scanning strategy is strip scanning to form 8Cr4Mo4V steel components.
[0019] In step one of this embodiment, a laser particle size analyzer was used to test the particle size distribution of the powder. The test conditions were: vacuum drying at 80℃ for 2 hours, experimental temperature: 25℃, and experimental humidity <40%. The powder morphology was observed using a Zeiss SIGMA 300 scanning electron microscope. The loose pack density of the bimodal particle size distribution 8Cr4Mo4V steel powder was 4.40~4.68 g / cm³. 3 The tap density is 5.02~5.29 g / cm³. 3 The fluidity is 22~32s / 50g; the morphology is mostly spherical or near-spherical, with only a small number of irregular spheres or satellite spheres.
[0020] In step two of this embodiment, the quality of 8Cr4Mo4V steel forming components is compared under different process parameters such as laser power and scanning speed. The process parameter window that is suitable for 8Cr4Mo4V steel powder with bimodal particle size distribution is preferred, and 8Cr4Mo4V steel components with dense microstructure and high surface quality are formed.
[0021] The additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size powder ratio described in this embodiment constructs an optimal bimodal particle size distribution system by adjusting the ratio of fine and coarse powders, and combines the matching and optimization of laser powder bed melting process parameters to achieve precision forming of 8Cr4Mo4V steel components with high density and high surface quality.
[0022] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the process of obtaining metal powder by gas atomization in step one involves spraying the molten metal liquid into an atomization tower through a nozzle, and then spraying high-pressure argon gas through an annular nozzle to impact the molten metal droplets, which solidify to obtain metal powder.
[0023] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the D50 of the fine powder in step 1 is 12~14μm, and the D50 of the coarse powder is 45~47μm.
[0024] This implementation method ensures that the bimodal distribution characteristics are obvious and the overlap is low.
[0025] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that in step one, the fine powder and coarse powder are mixed evenly at a mass ratio of 3:7.
[0026] This embodiment optimizes the ratio of fine powder to coarse powder.
[0027] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that, in step 1, the fine powder and coarse powder are placed into a high-speed mixer at a mass ratio of 2:8 to 3:7. Under the protection of an argon inert atmosphere, the speed of the mixer is controlled at 1000 revolutions per minute, and the mixture is mixed for 5 to 15 minutes.
[0028] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the loose packing density of the bimodal particle size distribution 8Cr4Mo4V steel powder in step one is 4.40~4.68 g / cm³. 3 The tap density is 5.02~5.29 g / cm³. 3 .
[0029] This embodiment optimizes the density properties of bimodal particle size distribution 8Cr4Mo4V steel powder.
[0030] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the flowability of the bimodal particle size distribution 8Cr4Mo4V steel powder in step one is 22~32s / 50g.
[0031] Specific Implementation Method Eight: This implementation method differs from one of the specific implementation methods one to seven in that the preheating temperature of the substrate is controlled to be 150~200℃ during the laser powder bed melting and forming process in step two.
[0032] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that in step two, the strip spacing is controlled to be 3~4mm and the interlayer rotation is 60°~70° during the laser powder bed melting and forming process.
[0033] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that in step 2, the laser power is controlled to be 240W, the scanning speed is 800~1200mm / s, and the scanning interval is 100μm.
[0034] This embodiment optimizes the parameters of the laser powder bed fusion molding process.
[0035] Specific Implementation Method Eleven: This implementation method differs from Specific Implementation Methods One through Ten in that the density of the 8Cr4Mo4V steel component obtained in step two reaches over 97%.
[0036] Example 1: This example describes an additive manufacturing method for 8Cr4Mo4V steel with a bimodal particle size distribution, implemented according to the following steps:
[0037] I. Preparation of 8Cr4Mo4V bearing steel powder using vacuum induction atomization powder preparation method: 8Cr4Mo4V bearing steel bars are placed in a vacuum induction furnace, heated and melted under vacuum, and then refined and degassed. The molten metal flows through a nozzle into an atomization tower, where it is ejected by high-pressure argon gas through an annular nozzle, impacting and breaking it into fine droplets. The droplets spheroidize due to surface tension and rapidly solidify to obtain metal powder. After sieving, fine powder with a particle size of 0.1~15μm and coarse powder with a particle size of 38~60μm are obtained. A high-speed mixer is used under an argon inert atmosphere at a speed of 1000 rpm for 5 minutes, mixing the fine and coarse powders at a mass ratio of 2:8 until homogeneous. After vacuum drying at 110℃, a bimodal particle size distribution 8Cr4Mo4V steel powder is obtained, with a loose packing density of 4.40 g / cm³. 3 The tap density is 5.02 g / cm³. 3 Flowability 32s / 50g;
[0038] II. Using 8Cr4Mo4V steel powder with a bimodal particle size distribution as raw material, a laser powder bed melting forming process was adopted. The laser power was controlled at 240~300W, the scanning speed at 600~1200mm / s, the scanning spacing at 100μm, the powder layer thickness at 30μm, the substrate preheating temperature at 180℃, the scanning strategy at strip scanning with a strip spacing of 3mm and interlayer rotation of 67°, to form 8Cr4Mo4V steel components.
[0039] In this embodiment, the powder morphology was observed using a Zeiss SIGMA 300 scanning electron microscope.
[0040] This embodiment uses Archimedes' displacement method to test the density of 8Cr4Mo4V components. The specific formula is as follows:
[0041] ρ s = (1-1)
[0042] ρ= (1-2)
[0043] Where, ρ s ρ represents the true density of the sample. L Let ρ be the density of water, ρ be the packing density of the sample, ρ0 be the theoretical density of the sample, m1 be the mass of the sample in air, and m2 be the mass of the sample suspended in water. Each sample was measured three times to avoid errors. The highest calculated packing density of the obtained component was 98.94%. The surface roughness of the component samples was measured using a white light interferometer, with each sample measured three times to avoid errors. The lowest calculated surface roughness of the obtained component was 2.031 μm.
[0044] The density of the component was tested using the Archimedes drainage method, and the surface roughness of the component sample was measured using a white light interferometer. The corresponding process parameters and test results are shown in Table 1.
[0045] Table 1. Density and roughness of formed components under various process parameters in Example 1
[0046]
[0047] Analysis of the data in the table shows that the density of the formed components is relatively low under various process parameters, approximately 95% to 98%. This may be related to the excessively high proportion of coarse powder under the 2:8 mass ratio of fine to coarse powder in the example. Under this ratio, the fine powder is insufficient to fully fill the gaps between the coarse powder, resulting in low loose powder density and compacted density, and insufficient density of the powder bed, which restricts the improvement of the density of the formed components.
[0048] Although the density needs improvement, the surface quality of the formed components is generally good under various process parameters, with the lowest surface roughness reaching 3.389 μm. Under constant laser power, the surface roughness of the formed components tends to increase with increasing scanning speed.
[0049] Example 2: This example describes an additive manufacturing method for 8Cr4Mo4V steel with a bimodal particle size distribution, implemented according to the following steps:
[0050] 1. 8Cr4Mo4V bearing steel rods were powdered using a vacuum induction atomization powdering method. After sieving, fine powder with a particle size of 0.1–15 μm and coarse powder with a particle size of 38–60 μm were obtained. The fine and coarse powders were mixed evenly at a mass ratio of 3:7 and then vacuum dried at 110℃ to obtain 8Cr4Mo4V steel powder with a bimodal particle size distribution. The loose pack density of the bimodal particle size distribution 8Cr4Mo4V steel powder was 4.68 g / cm³. 3 The tap density is 5.29 g / cm³. 3 Flowability 22s / 50g;
[0051] II. Using 8Cr4Mo4V steel powder with a bimodal particle size distribution as raw material, a laser powder bed melting forming process was adopted. The laser power was controlled at 240~300W, the scanning speed at 600~1200mm / s, the scanning spacing at 100μm, the powder layer thickness at 30μm, the substrate preheating temperature at 180℃, the scanning strategy at strip scanning with a strip spacing of 3mm and interlayer rotation of 67°, to form 8Cr4Mo4V steel components.
[0052] Figure 1 The particle size distribution diagram is shown for the 8Cr4Mo4V steel powder with a fine to coarse powder ratio of 3:7 and a bimodal particle size distribution prepared in Example 2. Figure 2 The image shows the SEM morphology of 8Cr4Mo4V steel powder with a fine to coarse powder ratio of 3:7 and a bimodal particle size distribution prepared in the example. It can be seen that the powder has good sphericity and only a small amount of irregularly shaped powder exists.
[0053] The process parameters used in the forming process and the density and roughness results of the formed components are shown in Table 2. Component No. 1, formed under the conditions of laser power of 240W, scanning speed of 600mm / s, and scanning spacing of 100μm, has the lowest surface roughness of 2.031μm. In summary, under the laser power conditions shown in Table 2 (process parameters in Example 2), the density and roughness of the formed components are as follows.
[0054] Table 2. Density and roughness of formed components under various process parameters in Example 2
[0055]
[0056] Analysis of the data in the table shows that components formed by laser powder bed melting of fine and coarse powders in a 3:7 mass ratio with bimodal particle size distribution have a high density, reaching 97%~99%. Compared to a 2:8 ratio, this ratio increases the fine powder content to 30%, which can more fully fill the gaps between coarse powder particles, significantly improving the loose and tapped density of the powder, resulting in a more compact powder bed structure and more uniform laser energy absorption, thus effectively improving the density of the formed components. Among them, component No. 4, formed under the conditions of laser power of 240W, scanning speed of 1200mm / s, and scanning spacing of 100μm, has the highest density, at 98.94%.
[0057] While obtaining high-density molded components, the surface quality of the molded components was also good under various process parameters. Component No. 1, formed under the conditions of laser power of 240W, scanning speed of 600mm / s, and scanning spacing of 100μm, had the lowest surface roughness of 2.031μm. Under constant laser power, the surface roughness showed the same trend as the 2:8 mass ratio powder molded components, that is, the surface roughness increased with increasing scanning speed. This is because the higher laser energy input at lower scanning speeds increases the amount of powder melting, improves the wettability and spreadability of the molten metal, thereby suppressing the spheroidization phenomenon caused by excessive surface tension, which helps to form continuous melt channels and improve the surface quality of the molded parts.
[0058] In summary, the No. 2 component, formed under the process parameters of 240W laser power, 800mm / s scanning speed, and 100μm scanning spacing, exhibits both high density (98.84%) and low surface roughness (2.888μm), demonstrating excellent overall forming quality and achieving a good match between high density and low roughness.
[0059] Comparing the quality of laser powder bed fusion molded components made from bimodal particle size distribution powders in Examples 1 and 2, it was found that, compared to the 2:8 mass ratio of fine to coarse bimodal powder which only showed better surface quality, the components formed using the 3:7 mass ratio of bimodal powder had both good density (97%~99%) and surface quality (minimum 2.031μm), and maintained stable forming quality over a wide range of process parameters, exhibiting a wider forming process window.
[0060] This invention proposes an additive manufacturing method for 8Cr4Mo4V steel based on a bimodal particle size distribution. By adjusting the mass ratio of fine powder (0~15μm) to coarse powder (38~60μm) to 2:8~3:7, a powder system with a distinct bimodal particle size distribution is constructed, thereby improving the powder bed packing density. Furthermore, by matching and optimizing the laser powder bed melting process parameters, the forming process window is broadened, enabling the forming of 8Cr4Mo4V steel components with high density and high surface quality.
[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit it. Any modifications or substitutions made by those skilled in the art to the embodiments described above should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method of additive manufacturing of 8Cr4Mo4V steel based on the proportioning of bimodal particle size powders, characterized in that The additive manufacturing method is implemented according to the following steps:
1. 8Cr4Mo4V bearing steel bars are heated and melted in a vacuum environment to obtain molten metal liquid. The molten metal liquid is then used to prepare metal powder by gas atomization powder preparation method. The metal powder is sieved to obtain fine powder with a particle size of 0.1~15μm and coarse powder with a particle size of 38~60μm. The fine powder and coarse powder are mixed evenly at a mass ratio of 2:8~3:
7. After vacuum drying, 8Cr4Mo4V steel powder with a bimodal particle size distribution is obtained.
2. Using 8Cr4Mo4V steel powder with a bimodal particle size distribution as raw material, a laser powder bed melting forming process is adopted. The laser power is controlled at 240~300W, the scanning speed is 600~1200mm / s, the substrate preheating temperature is 150~200℃, and the scanning strategy is strip scanning to form 8Cr4Mo4V steel components.
2. The method for additive manufacturing of 8Cr4Mo4V steel based on the proportioning of bimodal particle size powders according to claim 1, characterized in that In step one, the process of producing metal powder from molten metal using the gas atomization powdering method involves spraying molten metal into an atomization tower through a nozzle, and then spraying high-pressure argon gas through an annular nozzle to impact the molten metal droplets, which solidify to obtain metal powder.
3. The additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution according to claim 1, characterized in that... In step one, the fine powder has a D50 of 12~14μm, and the coarse powder has a D50 of 45~47μm.
4. The additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution according to claim 1, characterized in that... In step one, the fine powder and coarse powder are mixed evenly at a mass ratio of 3:
7.
5. The additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution according to claim 1, characterized in that... The loose bulk density of the bimodal particle size distribution 8Cr4Mo4V steel powder in step one is 4.40-4.68 g / cm 3 , and the tap density is 5.02-5.29 g / cm 3 .
6. The additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution according to claim 5, characterized in that... In step one, the flowability of the bimodal particle size distribution 8Cr4Mo4V steel powder is 22~32s / 50g.
7. The additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution according to claim 1, characterized in that... In step two, the preheating temperature of the substrate is controlled at 150~200℃ during the laser powder bed melting and forming process.
8. The additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution according to claim 1, characterized in that... In step two, the strip spacing is controlled to be 3-4 mm and the interlayer rotation is 60°-70° during the laser powder bed melting process.
9. The additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution according to claim 1, characterized in that... In step two, the laser power is controlled at 240W, the scanning speed is 800~1200mm / s, and the scanning interval is 100μm.
10. The additive manufacturing method for 8Cr4Mo4V steel based on bimodal particle size distribution according to claim 1, characterized in that... The density of the 8Cr4Mo4V steel component obtained in step two reaches over 97%.