A laser selective melting technology forming method and a d406a ultra-high strength steel used

Abstract

The application discloses a laser selective melting forming method in the technical field of additive manufacturing, and uses D406A ultra-high strength steel with low Mn content as a raw material, adopts a plasma rotating electrode atomization method to prepare metal powder, and then forms through a laser selective melting technology, so that D406A ultra-high strength steel printed parts with strength and impact performance equivalent to forged parts can be obtained through performance heat treatment. The D406A ultra-high strength steel formed through the laser selective melting has the advantages that the printed parts and the substrate can be separated through wire cutting without annealing, performance heat treatment can be directly carried out, and hot isostatic pressing treatment is not needed to reduce defects such as pores, so that the post-processing process is simplified, the production cycle is shortened, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, specifically to a laser selective melting forming method and the D406A ultra-high strength steel used therein. Background Technology

[0002] The rapid development of modern aerospace technology has presented new challenges to the extreme service performance of critical aircraft components, while the aerospace manufacturing industry has also placed higher demands on the comprehensive performance of major load-bearing components. Ultra-high strength steel, developed from structural steel, was created to meet these needs. It possesses extremely high room temperature tensile strength, along with excellent plasticity and toughness, fatigue resistance, fracture toughness, stress corrosion resistance, and good processability. It is widely used in cutting-edge fields such as aerospace and weaponry, including bulletproof steel plates, aircraft landing gear, and rocket engine casings.

[0003] 30Si2MnCrMoVE (D406A for short) is a low-alloy ultra-high-strength steel independently developed in my country. It possesses good plasticity and excellent impact resistance, among other mechanical properties. However, D406A ultra-high-strength steel is difficult to machine and has poor weldability, easily resulting in serious defects such as cracks, porosity, solid inclusions, and lack of fusion after welding. Furthermore, the scrap rate is high when machining complex D406A parts, and they cannot be integrally formed, requiring welding and riveting. Riveting methods often fail to achieve adequate sealing. Therefore, how to integrally form complex D406A parts while minimizing welding and riveting processes is one of the current challenges in the application of D406A ultra-high-strength steel.

[0004] Additive manufacturing technology integrates computer-aided design, materials processing and forming techniques, and uses digital model files as a basis to create physical objects by layering specialized materials through software and CNC machining. Compared to traditional subtractive manufacturing and forming manufacturing technologies, additive manufacturing simplifies the production process and avoids the disadvantages of long production cycles, high costs, and difficulty in producing complex parts. Metal additive manufacturing technology, as the most cutting-edge and promising technology in the entire additive manufacturing system, is an important development direction for advanced manufacturing technology and has been widely applied in aerospace, shipbuilding, petrochemical, and biomedical fields, promoting the development of the manufacturing industry. In recent years, China has acquired the capability to produce high-end products using additive manufacturing technology; however, the raw materials are limited, the alloy grades are few, and the processes are not yet fully developed.

[0005] To address the problem of poor weldability of D406A ultra-high strength steel, which leads to poor sealing of complex structural components, laser selective melting technology can be developed to form D406A ultra-high strength steel, along with its methods and processes. This will enable the one-piece forming of complex structural components, shorten the R&D cycle, reduce processing difficulty, and save costs. Summary of the Invention

[0006] This invention aims to provide a laser selective melting (LSM) forming method and the D406A ultra-high strength steel used in it. Addressing the problems of existing D406A ultra-high strength steel, such as easy formation of defects like porosity and cracks during welding, poor sealing of complex structural parts, and difficulty in integral forming, this invention provides a method and process for forming D406A ultra-high strength steel using LSM. The new D406A ultra-high strength steel has a lower Mn content and is more suitable for additive manufacturing. The D406A ultra-high strength steel formed by LSM achieves a density of over 99.7%, and its hardness after heat treatment can reach 590 HV. Its strength and impact resistance are comparable to forgings.

[0007] To address the above problems, the present invention provides the following technical solution:

[0008] A laser selective melting technology is used to form D406A ultra-high strength steel, the elemental composition of which is calculated by mass percentage as follows: C: 0.25-0.32%, Mn: 0.5-0.80%, Si: 1.5-1.66%, Cr: 1.1-1.2%, Ni: 0.23-0.26%, Mo: 0.48-0.52%, V: 0.10-0.15%, S≤0.001%, P≤0.004%, Cu≤0.05%, Al≤0.015%, Sn≤0.005%, Pb≤0.003%, Sb≤0.003%, Bi≤0.003%, with the remainder being Fe.

[0009] A laser selective melting forming method uses D406A ultra-high strength steel with low Mn content as raw material, prepares metal powder by plasma rotating electrode atomization, forms it by laser selective melting technology, and finally performs performance heat treatment.

[0010] Further, the process includes the following steps: S1: Powder preparation: The above-mentioned D406A ultra-high strength steel material is processed into electrode rod blanks, and then metal powder is prepared by plasma rotating electrode atomization method; S2: Powder sieving: The powder is sieved by vibration sieving in an argon-protected environment to select powder with a particle size of 15-53μm for later use; S3: Printing sample: The sample is printed using laser selective melting equipment. Before printing, argon gas is introduced into the forming chamber. Printing can begin when the oxygen content in the forming chamber is lower than 300ppm. The printed sample is obtained when the temperature is lower than 40℃; S4: Performance heat treatment: The printed sample is subjected to "normalizing + high-temperature tempering" heat treatment, followed by "quenching + low-temperature tempering" heat treatment.

[0011] Furthermore, S1, the rod size is Φ50mm×200~260mm, and the preparation conditions are: arc initiation at a rotation speed of 20000~30000r / min, electrode rod rotation speed of 20000~30000r / min, feed speed of 0.1~4mm / s, current of 500-2000mA, and argon gas is used as the atomizing medium and protective atmosphere in the powder preparation process.

[0012] Furthermore, the powder screened by S3 is placed into a powder storage bottle and filled with argon gas for protection.

[0013] Furthermore, the forming process parameters adopted by S4 are as follows: printing layer thickness 20-40μm, scanning spacing 0.05-0.2mm, scanning power 250-350W, scanning speed 500-1000mm / s, laser diameter 0.05-0.2mm, initial rotation angle 30°, and rotation increment 67°.

[0014] Furthermore, after printing, the printed parts can be directly separated by wire cutting without prior annealing.

[0015] A D406A ultra-high strength steel used in laser selective melting technology has the following elemental composition by mass percentage: C: 0.25–0.32%, Mn: 0.5–0.80%, Si: 1.5–1.66%, Cr: 1.1–1.2%, Ni: 0.23–0.26%, Mo: 0.48–0.52%, V: 0.10–0.15%, S≤0.001%, P≤0.004%, Cu≤0.05%, Al≤0.015%, Sn≤0.005%, Pb≤0.003%, Sb≤0.003%, Bi≤0.003%, with the remainder being Fe.

[0016] The working principle and beneficial effects of this invention:

[0017] (1) Using D406A ultra-high strength steel with low Mn content, a laser selective melting forming process suitable for D406A ultra-high strength steel was developed, which increased the types of alloys that can be used for laser selective melting forming and improved the metal additive manufacturing technology system.

[0018] (2) In this invention, D406A ultra-high strength steel powder is prepared by plasma rotating electrode atomization method. The powder has high sphericity and low oxygen content. The yield of powder with 15-53μm is greater than 50%, which significantly reduces the material cost of forming D406A ultra-high strength steel by laser selective melting technology.

[0019] (3) This invention uses laser selective melting forming technology to optimize key parameters such as scanning power and scanning speed, and successfully prepares printed sample parts without printing defects such as pores, inclusions, and cracks, and with a density greater than 99.7%. After heat treatment, the hardness can reach 590HV, and the strength and impact performance are comparable to forgings. No additional support is needed during the printing process to prevent cracking.

[0020] (4) The D406A ultra-high strength steel formed by laser selective melting can be separated from the substrate by wire cutting without annealing; it can be directly subjected to performance heat treatment without hot isostatic pressing to reduce defects such as pores, which simplifies the post-processing process, shortens the production cycle, and reduces the production cost. Attached Figure Description

[0021] Figure 1 The image shows the macroscopic morphology of the D406A ultra-high strength steel printed part in the embodiment;

[0022] Figure 2 The metallographic structure of the D406A ultra-high strength steel printed part before corrosion (without printing defects) in the example;

[0023] Figure 3 The metallographic structure of D406A ultra-high strength steel after printing corrosion in the example;

[0024] Figure 4 The metallographic structure of the D406A ultra-high strength steel printed part after heat treatment corrosion in the example is shown. Detailed Implementation

[0025] Example 1: This example uses a 15×15×80mm block sample as an example. The specific implementation steps are as follows:

[0026] The ultra-high strength steel used has the following elemental composition by mass percentage: C: 0.30%, Mn: 0.77%, Si: 1.60%, Cr: 1.2%, Ni: 0.26%, Mo: 0.50%, V: 0.13%, S: 0.001%, P: 0.003%, Cu: 0.03%, Al: 0.010%, Sn: 0.002%, Pb: 0.001%, Sb: 0.001%, Bi: 0.001%, with the remainder being Fe.

[0027] A laser selective melting technology forming method and the D406A ultra-high strength steel used therein, comprising the following steps:

[0028] Step 1, Powder Preparation: The above-mentioned D406A ultra-high strength steel material is processed into electrode rod blanks, which are then used to prepare metal powder using a plasma rotating electrode atomization method. The rod size is Φ50mm×220mm. The process involves arc initiation at 23000r / min, electrode rod rotation speed of 23000r / min, feed rate of 2mm / s, and current of 1300mA. Argon gas is used as the atomization medium and protective atmosphere during the powder preparation process.

[0029] Step 2, powder sieving: The powder is sieved by vibration sieving in an argon-protected environment to screen out powder with a particle size of 15-53μm for later use. The powder is then placed in a powder storage bottle and filled with argon for protection.

[0030] Step 3, Sample Printing: The sample is printed using a laser selective melting (SLM) system. The following process parameters were used: layer thickness 40 μm, scanning spacing 0.1 mm, scanning power 295 W, scanning speed 1000 mm / s, laser diameter 0.1 mm, initial rotation angle 30°, and rotation increment 67°. Argon gas was introduced into the forming chamber before printing began, and printing commenced when the oxygen content in the chamber was below 300 ppm. After printing, the sample was removed from the furnace when the temperature in the forming chamber was below 40°C.

[0031] Step 4, Performance Heat Treatment: The printed parts undergo "normalizing + high-temperature tempering" heat treatment, followed by "quenching + low-temperature tempering" heat treatment. The normalizing process involves holding at 920℃ for 3 hours and then air-cooling to room temperature; the high-temperature tempering process involves holding at 730℃ for 3 hours, furnace-cooling to below 600℃, and then air-cooling to room temperature; the quenching process involves holding at 920℃ for 3 hours and then oil-quenching to room temperature; the low-temperature tempering process involves holding at 330℃ for 5 hours and then air-cooling to room temperature.

[0032] Example 2: This example uses a block sample of 15×15×80mm as an example. The specific implementation steps are as follows:

[0033] The ultra-high strength steel used has the following elemental composition by mass percentage: C: 0.30%, Mn: 0.77%, Si: 1.60%, Cr: 1.2%, Ni: 0.26%, Mo: 0.50%, V: 0.13%, S: 0.001%, P: 0.003%, Cu: 0.03%, Al: 0.010%, Sn: 0.002%, Pb: 0.001%, Sb: 0.001%, Bi: 0.001%, with the remainder being Fe.

[0034] A laser selective melting technology forming method and the D406A ultra-high strength steel used therein, comprising the following steps:

[0035] Step 1, Powder Preparation: The above-mentioned D406A ultra-high strength steel material is processed into electrode rod blanks, which are then used to prepare metal powder using a plasma rotating electrode atomization method. The rod size is Φ50mm×220mm. The process involves arc initiation at 23000r / min, electrode rod rotation speed of 23000r / min, feed rate of 2mm / s, and current of 1300mA. Argon gas is used as the atomization medium and protective atmosphere during the powder preparation process.

[0036] Step 2, powder sieving: The powder is sieved by vibration sieving in an argon-protected environment to screen out powder with a particle size of 15-53μm for later use. The powder is then placed in a powder storage bottle and filled with argon for protection.

[0037] Step 3, Sample Printing: The sample is printed using a laser selective melting (SLM) system. The following process parameters are used: layer thickness 20 μm, scanning spacing 0.1 mm, scanning power 250 W, scanning speed 500 mm / s, laser diameter 0.1 mm, initial rotation angle 30°, and rotation increment 67°. Argon gas is introduced into the forming chamber before printing begins, and printing can commence when the oxygen content in the forming chamber is below 300 ppm. After printing, the sample is removed from the furnace when the forming chamber temperature is below 40°C.

[0038] Step 4, Performance Heat Treatment: The printed parts undergo "normalizing + high-temperature tempering" heat treatment, followed by "quenching + low-temperature tempering" heat treatment. The normalizing process involves holding at 950℃ for 3 hours and then air-cooling to room temperature; the high-temperature tempering process involves holding at 760℃ for 3 hours, furnace cooling to below 600℃, and then air-cooling to room temperature; the quenching process involves holding at 950℃ for 3 hours and then oil-quenching to room temperature; the low-temperature tempering process involves holding at 350℃ for 5 hours and then air-cooling to room temperature.

[0039] Example 3: This example uses a 15×15×80mm block sample as an example. The specific implementation steps are as follows:

[0040] The ultra-high strength steel used has the following elemental composition by mass percentage: C: 0.30%, Mn: 0.77%, Si: 1.60%, Cr: 1.2%, Ni: 0.26%, Mo: 0.50%, V: 0.13%, S: 0.001%, P: 0.003%, Cu: 0.03%, Al: 0.010%, Sn: 0.002%, Pb: 0.001%, Sb: 0.001%, Bi: 0.001%, with the remainder being Fe.

[0041] A laser selective melting technology forming method and the D406A ultra-high strength steel used therein, comprising the following steps:

[0042] Step 1, Powder Preparation: The above-mentioned D406A ultra-high strength steel material is processed into electrode rod blanks, which are then used to prepare metal powder using a plasma rotating electrode atomization method. The rod size is Φ50mm×220mm. The process involves arc initiation at 23000r / min, electrode rod rotation speed of 23000r / min, feed rate of 2mm / s, and current of 1300mA. Argon gas is used as the atomization medium and protective atmosphere during the powder preparation process.

[0043] Step 2, powder sieving: The powder is sieved by vibration sieving in an argon-protected environment to screen out powder with a particle size of 15-53μm for later use. The powder is then placed in a powder storage bottle and filled with argon for protection.

[0044] Step 3, Sample Printing: The sample is printed using a laser selective melting (SLM) system. The following process parameters were used: layer thickness 30 μm, scanning spacing 0.1 mm, scanning power 295 W, scanning speed 800 mm / s, laser diameter 0.1 mm, initial rotation angle 30°, and rotation increment 67°. Argon gas was introduced into the forming chamber before printing began, and printing commenced when the oxygen content in the chamber was below 300 ppm. After printing, the sample was removed from the furnace when the temperature in the forming chamber was below 40°C.

[0045] Step 4, Performance Heat Treatment: The printed parts undergo "normalizing + high-temperature tempering" heat treatment, followed by "quenching + low-temperature tempering" heat treatment. The normalizing process involves holding at 900℃ for 3 hours and then air-cooling to room temperature; the high-temperature tempering process involves holding at 700℃ for 3 hours, furnace cooling to below 600℃, and then air-cooling to room temperature; the quenching process involves holding at 900℃ for 3 hours and then oil-quenching to room temperature; the low-temperature tempering process involves holding at 300℃ for 5 hours and then air-cooling to room temperature.

[0046] Chemical composition analysis, tensile and AKU impact tests were performed on the printed D406A ultra-high strength steel, and the metallographic structure before and after heat treatment was observed. The following data were obtained:

[0047] Table 1. Chemical composition (wt.%) of D406A ultra-high strength steel printed parts

[0048]

[0049] Table 2 Properties of D406A Ultra-High Strength Steel Printed and Forged Parts

[0050]

[0051] The results are as follows Figure 3 , Figure 4 As shown in Tables 1 and 2, analysis of Table 1 reveals that the chemical composition of the printed parts conforms to the range of ultra-high strength steel. Analysis of Table 2 shows that the printer's strength and impact performance are comparable to forgings, while its yield strength is stronger. From... Figure 2 It can be seen that the metallographic structure of the printed part before etching has no printing defects. From Figure 3 and Figure 4 It can be seen that no overheated structure or obvious delamination was found in the microstructure after heat treatment.

[0052] The embodiments of the present invention have been described above. Various modifications and improvements can be made without departing from the inventive concept, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A laser selective melting technology forming method, characterized in that, Using low-Mn-content D406A ultra-high-strength steel as raw material, metal powder is prepared by plasma rotating electrode atomization, then shaped by laser selective melting technology, and finally subjected to performance heat treatment. The process includes the following steps: S1: Powder preparation: The above-mentioned D406A ultra-high strength steel material is processed into electrode rod blanks, and then metal powder is prepared by plasma rotating electrode atomization method. S2: Powder sieving: The powder is sieved by vibration sieving under argon protection to select powder with a particle size of 15-53μm for later use. S3: Printed Sample: The sample is formed by laser selective melting equipment. Argon gas is introduced into the forming chamber before printing begins. Printing begins when the oxygen content in the forming chamber is below 300ppm. The sample is removed from the furnace when the temperature is below 40℃. S4: Performance heat treatment: The printed parts are subjected to "normalizing + high temperature tempering" heat treatment, followed by "quenching + low temperature tempering" heat treatment. S1. The rod size is Φ50mm×200~260mm. Preparation conditions: arc initiation at a rotation speed of 20000~30000r / min, electrode rod rotation speed of 20000~30000r / min, feed speed of 0.1~4mm / s, current of 500-2000mA, and argon gas is used as the atomizing medium and protective atmosphere in the powder preparation process. D406A ultra-high strength steel powder is prepared by plasma rotating electrode atomization method, with a powder yield of 15~53 μm >50%. The forming process parameters used in S4 are as follows: printing layer thickness 20–40 μm, scanning spacing 0.05–0.2 mm, scanning power 250–350 W, scanning speed 500–1000 mm / s, laser diameter 0.05–0.2 mm, initial rotation angle 30°, and rotation increment 67°; the S4 normalizing process is 900–950℃, held for 1–3 hours, and air-cooled to room temperature; the high-temperature tempering process is 700–760℃, held for 1–3 hours, furnace-cooled to below 600℃, and then air-cooled to room temperature; the quenching process is 900–950℃, held for 1–3 hours, and oil-quenched to room temperature; the low-temperature tempering process is 300–350℃, held for 2–7 hours, and then air-cooled to room temperature. Cool to room temperature; after printing, the printed parts are directly separated by wire cutting without prior annealing; the elemental composition is calculated as a percentage by mass: C: 0.25~0.32%, Mn: 0.5~0.80%, Si: 1.5~1.66%, Cr: 1.1~1.2%, Ni: 0.23~0.26%, Mo: 0.48~0.52%, V: 0.10~0.15%, S≤0.001%, P≤0.004%, Cu≤0.05%, Al≤0.015%, Sn≤0.005%, Pb≤0.003%, Sb≤0.003%, Bi≤0.003%, with the remainder being Fe.

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