A method for preparing a selective laser melting Cr4Mo4V series steel structural part

Abstract

The application discloses a preparation method of a selective laser melting Cr4Mo4V series steel structural part, and aims at the problems of large carbide size of the existing bearing steel and machining difficulty of a complex structural part. The preparation method of the selective laser melting Cr4Mo4V series steel structural part comprises the following steps: firstly, preparing a steel powder from a Cr4Mo4V series steel rod through a gas atomization method; secondly, adopting the steel powder to perform selective laser melting forming; under an inert protective atmosphere, the laser power is controlled to be 210-330 W, the scanning speed is controlled to be 500-1700 mm / s, the scanning interval is controlled to be 60-120 µm, the layer thickness is controlled to be 30-50 µm, the energy density is controlled to be 50-85 J / mm 3 , and the substrate temperature is controlled to be 150-250 ℃, so that the Cr4Mo4V series steel structural part is obtained through laser melting forming. The powder is prepared through the gas atomization process, the defect density and thermal cracks are reduced by optimizing the selective laser melting parameters, and therefore the forming capacity of the component is improved.

Description

Technical Field

[0001] This invention belongs to the field of metal material preparation technology, specifically relating to a method for preparing Cr4Mo4V series steel structural parts by selective laser melting. Background Technology

[0002] High-carbon, high-alloy, high-temperature bearing steels, represented by 8Cr4Mo4V, are typical materials for main shaft bearings in aero-engines. With increasing bearing integration, bearing structures are becoming increasingly complex, posing a significant challenge to conventional machining methods. Furthermore, the inherent uneven distribution and tendency to aggregate large-sized primary carbides in 8Cr4Mo4V steel can lead to fatigue cracking in bearing components, thus affecting bearing life. Therefore, 3D printing technology offers a new approach to solving these problems.

[0003] Selective Laser Melting (SLM) is an additive manufacturing method that achieves rapid prototyping by melting powder layer by layer. Compared with traditional forming methods, SLM printing of complex bearing rings has advantages such as strong structural design, ease of forming, and reduced carbide size. At the same time, the introduction of powder preparation technology can eliminate the hidden dangers caused by large carbide size, which has significant advantages in the forming of complex components.

[0004] However, selective laser melting (SLM) is characterized by rapid thermal cycling, which easily leads to large temperature gradients and residual stresses within the material. This is especially true for high-alloy steels such as 8Cr4Mo4V, where the defect density and risk of hot cracking in components increase dramatically. Based on this consideration, there are few reports on the preparation process of Cr4Mo4V series high-carbon high-alloy steels using selective laser melting (SLM). Therefore, there is an urgent need to conduct related technical research to obtain an SLM forming process that can significantly reduce the risk of cracking and improve the formability of high-carbon high-alloy components. Summary of the Invention

[0005] This invention addresses the technical problems of large carbide size and difficult machining of complex structural parts in existing bearing steels by providing a method for preparing Cr4Mo4V steel structural parts by selective laser melting.

[0006] The method for preparing Cr4Mo4V steel structural components by selective laser melting of the present invention is implemented according to the following steps:

[0007] 1. Cr4Mo4V steel rods are prepared into steel powder with a particle size of 15~53µm by gas atomization.

[0008] II. Selective laser melting and forming are performed using the steel powder obtained in step I. Under an inert protective atmosphere, the laser power is controlled at 210~330W, the spot diameter at 65µm, the scanning speed at 500~1700mm / s, the scanning spacing at 60~120µm, the layer thickness at 30~50µm, and the energy density at 50~85J / mm². 3 The substrate temperature is 150~250℃, the scanning strategy is an interlayer scanning direction interval of 60°~70°, and the Cr4Mo4V steel structure is obtained by laser melting.

[0009] The powder produced by this invention via gas atomization exhibits high sphericity, uniform particle size distribution, and no obvious hollow or irregularly shaped powder. The use of a preheated substrate reduces the risk of thermal cracking in high-carbon steel materials.

[0010] Compared with existing technologies, the selective laser melting method for preparing Cr4Mo4V steel structural components of this invention has the following advantages:

[0011] 1) This invention prepares 8Cr4Mo4V steel powder by gas atomization. The powder has high sphericity, uniform particle size distribution, and no obvious hollow powder or irregular powder, which effectively improves the quality of the formed parts.

[0012] 2) The selective laser melting (SLM) method for preparing Cr4Mo4V series steel described in this invention involves preparing powder through gas atomization and then shaping the steel powder through selective laser melting. By optimizing the selective laser melting parameters, the defect density and hot cracks are reduced, and the forming capability of the components is improved. This fills the research gap in SLM forming technology for high-carbon and high-alloy steels such as Cr4Mo4V series, and provides research ideas for further improving the forming of complex components of 8Cr4Mo4V steel by selective laser melting.

[0013] 3) The preparation method provided by the present invention produces a finer and more uniform microstructure, which is beneficial to the mechanical properties of the molded part.

[0014] In summary, the powder preparation technology of 8Cr4Mo4V steel of this invention is reasonable, optimizes the selective laser melting parameters, has good forming ability, high density, fine and uniform microstructure, and the density can reach 99%, thereby improving the forming ability and mechanical properties of selective laser melting for 8Cr4Mo4V steel. Attached Figure Description

[0015] Figure 1 The image shown is a SEM image of the 8Cr4Mo4V steel powder prepared in the example.

[0016] Figure 2 The images show the metallographic structures of 8Cr4Mo4V steel obtained by selective laser melting at different energy densities in the examples, where (a) E = 30.88 J / mm 3(P=210W, v=1700mm / s), (b) E=53.57J / mm 3 (P=300W, v=1400mm / s), (c) E=61.36J / mm 3 (P=270W, v=1100mm / s), (d) E=68.18J / mm 3 (P=300W, v=1100mm / s), (e) E=105J / mm 3 (P=210W, v=500mm / s);

[0017] Figure 3 The image shows the metallographic structure of 8Cr4Mo4V steel obtained by selective laser melting in the example when P=270W, v=1100mm / s, and h=100µm.

[0018] Figure 4 The image shown is a SEM image of selective laser melting of 8Cr4Mo4V steel at P=270W, v=1100mm / s, and h=100µm in the example. Detailed Implementation

[0019] Specific Implementation Method 1: The method for preparing Cr4Mo4V steel structural components using selective laser melting in this implementation method is carried out according to the following steps:

[0020] 1. Cr4Mo4V steel rods are prepared into steel powder with a particle size of 15~53µm by gas atomization.

[0021] II. Selective laser melting and forming are performed using the steel powder obtained in step I. Under an inert protective atmosphere, the laser power is controlled at 210~330W, the spot diameter at 65µm, the scanning speed at 500~1700mm / s, the scanning spacing at 60~120µm, the layer thickness at 30~50µm, and the energy density E is controlled at 50~85J / mm². 3 The substrate temperature is 150~250℃, the scanning strategy is an interlayer scanning direction interval of 60°~70°, and the Cr4Mo4V steel structure is obtained by laser melting.

[0022] This implementation requires controlling the energy density of the selective laser melting process. When the energy density is less than approximately 50 J / mm², 3 At that time, the formed part contains porous defects; when the energy density is approximately 50~85 J / mm² 3 At that time, the formed part contains a small number of holes and small cracks; when the energy density is greater than about 85 J / mm², the part will have a small number of defects. 3 At that time, the formed parts often contained cracks and defects.

[0023] This embodiment reduces the defect density and cracking risk of the formed parts by adjusting parameters such as laser power, scanning speed, and scanning spacing, thereby improving the forming ability of selective laser melting for 8Cr4Mo4V steel and obtaining 8Cr4Mo4V steel structural parts with high density and fine and uniform microstructure.

[0024] Specific Implementation Method Two: The difference between this implementation method and Specific Implementation Method One is that the Cr4Mo4V series steel bar mentioned in step one is an 8Cr4Mo4V steel bar.

[0025] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the gas atomization method described in step 1 involves heating a Cr4Mo4V steel bar until it melts to form a liquid metal. The liquid metal is then broken up by high-speed argon gas impact and (rapidly) cooled to obtain steel powder.

[0026] The gas atomization method in this embodiment prepares powder under an argon protective atmosphere, which reduces the oxidation rate and improves the purity of the powder; the atomization process involves rapid cooling, resulting in uniform element distribution and no obvious element enrichment or depletion.

[0027] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the steel powder is dried at a temperature of 80°C in step one.

[0028] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that the inert protective atmosphere described in step 2 is an argon protective atmosphere.

[0029] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the gas pressure is controlled at 0.4~0.6MPa during the selective laser melting and forming process in step two.

[0030] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that the energy density is controlled to be 55~70 J / mm² during the selective laser melting and forming process in step two. 3 The formula for calculating energy density E is:

[0031]

[0032] In the formula, P is the laser power (W); v is the scanning speed (mm / s); h is the scanning spacing (μm); and H is the layer thickness (μm).

[0033] Specific Implementation Method Eight: This implementation method differs from one of the specific implementation methods one to seven in that the substrate temperature is controlled at 200°C in step two.

[0034] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that in step two, the laser power is controlled to be 250~300W, the spot diameter is 65µm, the scanning speed is 1000~1300mm / s, the scanning spacing is 90~120µm, and the layer thickness is 35~45µm.

[0035] Specific Implementation Method 10: This implementation method differs from Specific Implementation Method 9 in that in step two, the laser power is controlled at 270W, the spot diameter is 65µm, the scanning speed is 1100mm / s, the scanning interval is 100µm, the layer thickness is 40µm, and the scanning strategy is an interlayer scanning direction interval of 67°.

[0036] Example 1: The method for preparing Cr4Mo4V steel structural components by selective laser melting in this example is implemented according to the following steps:

[0037] 1. Steel powder with a particle size of 15~53µm was prepared from 8Cr4Mo4V steel rod by gas atomization. The 8Cr4Mo4V steel powder was pretreated at 80℃ and dried for 9h.

[0038] 2. Selective laser melting and forming were performed using the steel powder obtained in step 1. The back vacuum was 4 mbar, and the forming was carried out under an argon protective atmosphere (argon pressure of about 0.5 MPa). The laser power was controlled at 210~330W, the spot diameter was 65µm, the scanning speed was 500~1700mm / s, the scanning interval was 100µm, the layer thickness was 40µm, the substrate temperature was 200℃, and the scanning strategy was an interlayer scanning direction interval of 67°. The resulting 8Cr4Mo4V steel structural parts were formed.

[0039] This embodiment is provided by Figure 1 It can be seen that steel powder is prepared by gas atomization using 8Cr4Mo4V steel rod as raw material. The steel powder has a particle size of 15~53µm, good sphericity, uniform particle size distribution, and no obvious hollow powder or irregular powder.

[0040] See Figure 2 The metallographic structure of the 8Cr4Mo4V steel prepared in this embodiment was observed, and the defect types and density varied with different parameter combinations. Energy density has a significant impact on the density of the formed parts. For selective laser melting of 8Cr4Mo4V steel under different parameter combinations, when the energy density is less than approximately 50 J / mm², the density of the formed parts is significantly affected. 3 At that time, the formed parts often exhibit porous defects (e.g., energy density E=30.88 J / mm). 3 (P=210W, v=1700mm / s); when the energy density is approximately 50~85J / mm 3 At this time, the formed parts often exhibit a small number of holes (e.g., E=53.57J / mm). 3(P=300W, v=1400mm / s) and small crack defects (e.g., E=68.18J / mm) 3 (P=300W, v=1100mm / s), while when E=61.36J / mm 3 When P=270W, v=1100mm / s, the metallographic cross-section shows no obvious defects; when the energy density is greater than approximately 85J / mm², the cross-section shows no obvious defects. 3 At this time, the formed parts often exhibit crack defects (e.g., E=105J / mm). 3 (P=210W, v=500mm / s). The formula for calculating energy density is:

[0041]

[0042] In the formula, P is the laser power (W); v is the scanning speed (mm / s); h is the scanning spacing (μm); and H is the layer thickness (μm).

[0043] The density of the molded part prepared in this embodiment was tested using the Archimedes drainage method, and it was approximately 92% to 99%.

[0044] Example 2: The method for preparing Cr4Mo4V steel structural components by selective laser melting in this example is implemented according to the following steps:

[0045] 1. Steel powder with a particle size of 15~53µm was prepared from 8Cr4Mo4V steel rod by gas atomization. The 8Cr4Mo4V steel powder was pretreated at 80℃ and dried for 9h.

[0046] 2. Selective laser melting was performed using the steel powder obtained in step 1. Based on Example 1, the influence of scanning distance was further investigated, and the selective laser melting parameters were optimized. The molding was carried out under an argon protective atmosphere. The laser power was controlled at 270W, the spot diameter at 65µm, the scanning speed at 1100mm / s, and the scanning distances at 60µm, 80µm, 100µm, and 120µm, respectively. The layer thickness was 40µm, the substrate temperature was 200℃, and the scanning strategy was a 67° interval between the scanning directions of the layers. The resulting 8Cr4Mo4V steel structural component was formed.

[0047] The density of the molded parts prepared in this embodiment was tested using the Archimedes drainage method, and the density was approximately 98.5% to 99%. The highest density was achieved when the scanning interval was 100 µm.

[0048] Please see Figure 3 When P=270W, v=1100mm / s, h=100µm, the metallographic structure of selective laser melting of 8Cr4Mo4V steel was observed. The molten pools overlapped well and the powder was fully fused.

[0049] Please see Figure 4 When P=270W, v=1100mm / s, and h=100µm, the SEM image of selective laser melting of 8Cr4Mo4V steel shows a fine and uniform microstructure, which is beneficial to eliminating microstructure anisotropy and improving the mechanical properties of the material.

[0050] This invention discloses a method for preparing Cr4Mo4V series steel structural components using selective laser melting (SLM). Using 8Cr4Mo4V steel bars as the raw material, the powder is prepared by gas atomization, and then shaped using selective laser melting (SLM). By optimizing the SLM parameters, 8Cr4Mo4V steel with good formability is obtained. The powder preparation technology of this invention for 8Cr4Mo4V steel is reasonable, the SLM parameters are appropriate, resulting in good formability, high density, and fine and uniform microstructure, thus improving the formability and mechanical properties of 8Cr4Mo4V steel using SLM.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing Cr4Mo4V steel structural components by selective laser melting, characterized in that... The method for preparing the selected area laser melting Cr4Mo4V steel structural component is implemented according to the following steps:

1. Cr4Mo4V steel rods are prepared into steel powder with a particle size of 15~53µm by gas atomization. II. Selective laser melting and forming were performed using the steel powder obtained in step one. Under an inert protective atmosphere, the laser power was controlled at 270W, the spot diameter at 65µm, the scanning speed at 1100mm / s, the scanning spacing at 100µm, the layer thickness at 40µm, and the energy density E at 61.36J / mm². 3 The substrate temperature is 150~250℃, the scanning strategy is an interlayer scanning direction interval of 67°, and the Cr4Mo4V steel structure is obtained by laser melting forming. The gas atomization method described in step one involves heating a Cr4Mo4V steel bar until it melts to form a liquid metal. The liquid metal is then broken up by high-speed argon gas impact and cooled to obtain steel powder. In step two, the gas pressure is controlled to be 0.4~0.6MPa during the selective laser melting process.

2. The method for preparing Cr4Mo4V steel structural components by selective laser melting according to claim 1, characterized in that... The Cr4Mo4V series steel bar mentioned in step one is an 8Cr4Mo4V steel bar.

3. The method for preparing Cr4Mo4V steel structural components by selective laser melting according to claim 1, characterized in that... In step one, the steel powder is dried at a temperature of 80°C.

4. The method for preparing Cr4Mo4V steel structural components by selective laser melting according to claim 1, characterized in that... The inert protective atmosphere mentioned in step two is an argon protective atmosphere.

5. The method for preparing Cr4Mo4V steel structural components by selective laser melting according to claim 1, characterized in that... In step two, the substrate temperature is controlled at 200℃.

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