A method for producing 24crni mo alloy steel

Abstract

The application discloses a method for preparing 24CrNiMo alloy steel, comprising the following steps: S1, preparation of 24CrNiMo alloy steel powder and pretreatment before printing; S2, construction of a three-dimensional model of electron beam selective melting forming 24CrNiMo forming steel; S3, electron beam selective melting printing of 24CrNiMo alloy steel; the application is based on the additive manufacturing method for preparing 24CrNiMo alloy steel by electron selective melting, and in-situ heat treatment is realized under high vacuum degree, high preheating temperature and high electron beam rapid scanning on a powder bed. The 24CrNiMo alloy steel prepared by the application has the characteristics of uniform forming structure, few defects, high density, high strength and hardness.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of additive manufacturing of low alloy steel, in particular to a method for preparing 24CrNiMo alloy steel. BACKGROUND

[0002] 24CrNiMo steel is a high-strength low-alloy steel, which has high ultimate tensile strength, good fracture toughness and thermal stability, and is widely used as a raw material for brake discs. Currently, the brake discs of high-speed trains are mainly formed by casting and forging.

[0003] Electron beam selective melting (SEBM) is a kind of electron beam additive manufacturing technology, which can manufacture three-dimensional metal parts by scanning and melting powder materials layer by layer. The energy density is high, the material application range is wide, the manufacturing process is in a vacuum environment, the scanning speed is 4-5 times faster than that of laser, the preheating temperature can reach 1100℃, and the formed parts have the characteristics of small residual stress, which has been successfully applied in the fields of aerospace, biological medicine and the like.

[0004] Currently, electron beam selective melting technology has realized the forming of difficult-to-form metal materials such as lightweight metal materials, medium-entropy alloys, Ti-Al high-temperature alloys and refractory and difficult-to-weld metal materials. SEBM has a high preheating temperature, and long-time construction can produce stress relief annealing. Compared with SLM, the formed parts have lower residual stress. Using appropriate process parameters, the density of metal and alloy can reach nearly 100%. Through microstructure analysis of H13 tool steel produced by SEBM, there is almost no porosity, and the structure is martensite with high hardness. The Ti-6Al-4V titanium-based alloy manufactured by SEBM has strength and elongation comparable to the best titanium forged products under suitable process parameters. Therefore, compared with traditional casting and forging brake discs, the electron beam selective melting method can be used as a new manufacturing method to form 24CrNiMo alloy steel for manufacturing brake discs. SUMMARY

[0005] To solve the above technical problems, the present application provides a method for preparing 24CrNiMo alloy steel.

[0006] The technical scheme of the present application is: a method for preparing 24CrNiMo alloy steel, comprising the following steps:

[0007] S1, preparation of 24CrNiMo alloy steel powder and pretreatment before printing:

[0008] The 24CrNiMo alloy steel powder with a particle size of 50-120μm is prepared by using the gas atomization method, and the raw materials of the 24CrNiMo alloy steel powder are as follows in percentage by mass: C: 0.20-0.25%, Cr: 0.95-1.2%, Ni: 0.95-1.25%, Si: 0.2-0.4%, Mo: 0.4-0.8%, Mn: 0.6-1.2%, and the balance is Fe element;

[0009] The 24CrNiMo alloy steel powder is dried again;

[0010] S2, constructing an electron beam selective melting, shaping a three-dimensional model of the 24CrNiMo alloy steel:

[0011] A three-dimensional machining platform and a machining part are constructed in sequence, the machining part has a size of x=15mm, y=15mm, and z=10mm, the machining part is subjected to a slice processing of the three-dimensional model to obtain data, the data is subjected to path planning to form an STL format file, and the STL format file is imported into an electron beam selective melting device;

[0012] S3, printing the 24CrNiMo alloy steel by using the electron beam selective melting:

[0013] The printing process parameters of the electron beam selective melting device are set according to the STL format file, the forming bin in the electron beam selective melting device is subjected to substrate leveling and powder filling, the powder bed chamber of the electron beam selective melting device is subjected to vacuumizing treatment, when the vacuum degree reaches 7.5×10 -1 The vacuum degree is maintained for 2-3min, then the high-voltage power supply is turned on to 60KV, and the electron beam is centered after the high voltage is stabilized;

[0014] Then the substrate preheating is started, and the current and the scanning speed are adjusted, after the substrate preheating is completed, the powder bed preheating is started, and the powder bed preheating is completed to start the printing, and the 24CrNiMo alloy steel is obtained.

[0015] Further, in the step S1, the 24CrNiMo alloy steel powder is prepared by using the gas atomization method, and the steps are as follows:

[0016] S1-1: The raw materials of the 24CrNiMo alloy steel are added into an electromagnetic induction furnace according to the proportion to be melted, the melting temperature is 1600-1650℃, the melting time is 55-65min, argon protection is adopted, and the molten metal is obtained after the melting is completed;

[0017] S1-2: The molten metal is connected to the atomizing nozzle to flow out at a speed of 7-9kg / min, and meets the high-speed airflow at the atomizing nozzle, the air pressure of the high-speed airflow is 3.5-4.5MPa, and the alloy powder is obtained;

[0018] S1-3: Screen the alloy powder to obtain 24CrNiMo alloy steel powder, and place it in a drying box at 115-125°C for drying.

[0019] Description: The powder prepared by the gas atomization powder preparation technology has the advantages of high sphericity, good flowability, low O, N, and H content, and large adjustable range of powder particle size distribution.

[0020] Further, in step S1, the drying treatment is continuous drying, and the temperature of the continuous drying is 60-80°C, and the time is 20-40 min.

[0021] Description: The higher the drying temperature, the more likely it is to cause the surface of the object to be too dry while the inside is still moist, resulting in uneven drying. In this case, it will lead to an increase in drying time. If the drying temperature is too low, it will cause the material to have too much moisture, which will affect the subsequent forming effect.

[0022] Further, in step S3, the printing process parameters are: power current 6-16 mA, scanning speed 3.5-6.5 m / s, powder taking amount 0.09-0.12 mm, pre-powder thickness 50 μm, beam spot defocusing amount -0.500 V, and beam spot size 0.100 mm.

[0023] Description: The forming precision of the part is adjusted by adjusting the above printing process parameters.

[0024] Further, in step S3, during the vacuum pumping process, the rotation speed of the vacuum pump is 60,000 r / min, and the rotation speed of the electron gun molecular pump is 72,000 r / min.

[0025] Description: When the rotation speed of the vacuum pump is too high, it may cause wear and tear and premature failure of the parts. High-speed rotation may cause mechanical damage or overheating, resulting in a shortened life of the pump. When the rotation speed of the vacuum pump is too low, it may not be able to achieve the required vacuum degree or flow rate. This may result in reduced work efficiency or failure to complete the task.

[0026] Further, in step S3, the substrate preheating is divided into three stages: the first stage is preheated to 100°C with a current of 5 mA, then changed to a current of 10 mA to preheat to 240-260°C and keep for 5-10 min; the second stage is preheated to 590-610°C with a current of 15 mA and kept for 5-10 min; the third stage is preheated to 840-860°C with a current of 20 mA and kept for 5-10 min.

[0027] Description: The staged preheating of the substrate is an important process in electron beam selective melting, which can reduce thermal stress, volatilize volatile components, and protect the surface coating of the substrate, ensuring the quality and stability of the melting process.

[0028] Further, in step S3, the maximum current of the powder bed preheating is 48.0 mA, the average current of the powder bed preheating is 12.00-16.00 mA, the minimum time of the powder bed preheating is 8.00-18.00 s, the maximum time of the powder bed preheating is 16.00-25.00 s, and the total preheating time of the powder bed preheating is ≥ the minimum time of the preheating + the maximum time of the preheating.

[0029] Description: The powder bed preheating is to avoid powder blowing caused by too fast temperature drop, and to consolidate the powder bed surface for printing 24CrNiMo steel.

[0030] Further, in step S1, the drying treatment is:

[0031] First, the 24CrNiMo alloy steel powder is subjected to a dehumidification treatment at 110-120℃ for 15-20 min, and a hydrogen gas flow is sprayed to the 24CrNiMo alloy steel powder for dispersion treatment during the dehumidification process, and the spraying rate of the gas flow is 15-25 mL / min.

[0032] Then, the 24CrNiMo alloy steel powder after the dehumidification treatment is subjected to a variable-temperature microwave drying to obtain the 24CrNiMo alloy steel powder after the drying treatment.

[0033] Description: First, the dehumidification treatment at low temperature can help to remove moisture from the powder, reducing the moisture on the surface or inside of the powder to a lower level before high-temperature drying, and reducing its impact on the drying process; and the hydrogen gas flow is sprayed during the dehumidification at low temperature to disperse the powder, which can reduce the oxidation of the powder surface, improve the purity of the powder, and improve the flowability of the powder, reduce the chance of powder caking, and prevent powder adhesion.

[0034] Then, the variable-temperature microwave drying after the dehumidification treatment can rapidly propagate the microwave energy inside the powder, making the powder heat evenly and dry more evenly; and through variable-temperature treatment, the drying temperature and microwave power can be flexibly adjusted to avoid energy waste and prolong the drying time; and the chemical changes in the powder and the loss of heat-sensitive substances can be reduced, better maintaining the composition and properties of the powder, thereby improving the quality of the dried powder.

[0035] Further, the variable-temperature microwave drying is: first, microwave drying at 140-150℃ for 3-5 min, the microwave frequency is 650-680 W; then, microwave drying at 125-135℃ for 5-10 min, the microwave frequency is 450-500 W; finally, microwave drying at 140-150℃ for 3-5 min, the microwave frequency is 650-680 W.

[0036] Explanation: First, short-time microwave drying is carried out at high temperature and high power, which can rapidly evaporate the moisture on the surface of the powder, so that the initial drying speed is faster, thereby reducing the humidity of the powder in a shorter time; then, long-time microwave drying is carried out at medium temperature and medium power, which can further more gently control the humidity and temperature change of the powder, continuously evaporate the moisture of the powder, improve the overall drying uniformity, and avoid causing excessive drying or quality damage; finally, short-time drying at high temperature and high power can speed up the overall drying process of the powder, ensure that the humidity of the powder is further reduced, and reach the required drying level.

[0037] The beneficial effects of the present application are:

[0038] (1) The present application prints 24CrNiMo alloy steel by electron beam selective melting, which belongs to a new 24CrNiMo alloy steel forming process, and the 24CrNiMo alloy steel is formed by high-energy electron beam selective melting under vacuum conditions, which can effectively prevent oxidation behavior due to excessively high temperature, and the formed 24CrNiMo alloy steel has good surface quality, refined structure and uniform composition.

[0039] (2) Compared with the traditional process, the method of the present application can overcome various casting defects, low yield and the problem that the forming structure is limited in the forging process; electron beam selective melting forming can realize in-situ stress relief annealing, and the formed 24CrNiMo alloy steel has good forming quality, high density and excellent performance of high toughness and high strength.

[0040] (3) Compared with the alloy steel prepared by laser additive manufacturing, the present application prints the sample at a higher preheating temperature, which can effectively reduce residual stress and prevent cracking and other defects, has a vacuum condition, can prevent high-temperature oxidation, and obtain uniform bainite alloy steel under suitable process parameters and fast cooling speed. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is 24CrNiMo alloy steel prepared by electron beam selective melting of the present application;

[0042] Figure 2 is the SEM surface morphology diagram of 24CrNiMo powder prepared by the gas atomization method of the present application;

[0043] Figure 3 is the SEM bainite structure in example 1 in the present application;

[0044] Figure 4 is the SEM bainite structure in example 2 in the present application. DETAILED DESCRIPTION

[0045] The application will be described in further detail below with reference to the specific embodiments, so as to better reflect the advantages of the application.

[0046] Embodiment 1

[0047] A method for preparing 24CrNiMo alloy steel, comprising the following steps:

[0048] S1, preparation of 24CrNiMo alloy steel powder and pretreatment before printing:

[0049] The 24CrNiMo alloy steel powder with a particle size of 60-100 μm is prepared by using gas atomization method, and the raw materials of the 24CrNiMo alloy steel powder are as follows in terms of mass percentage: C: 0.23%, Cr: 1.05%, Ni: 1.1%, Si: 0.3%, Mo: 0.6%, Mn: 0.9%, and the balance is Fe element;

[0050] The steps for preparing the 24CrNiMo alloy steel powder by using gas atomization method are as follows:

[0051] S1-1: The raw materials of the 24CrNiMo alloy steel are added into an electromagnetic induction furnace according to the proportion for smelting, the smelting temperature is 1625℃, the smelting time is 60 min, argon protection is adopted, and the molten metal is obtained after smelting;

[0052] S1-2: The molten metal is connected to the atomizing nozzle, and flows out at a speed of 8 kg / min, and meets the high-speed airflow at the atomizing nozzle, the air pressure of the high-speed airflow is 4.0 MPa, and the alloy powder is obtained;

[0053] S1-3: The alloy powder is sieved to obtain the 24CrNiMo alloy steel powder, which is placed in a drying box at 120℃ for drying;

[0054] The 24CrNiMo alloy steel powder is further dried, and the drying treatment is continuous drying, the temperature of the continuous drying is 70℃, and the time is 30 min;

[0055] S2, constructing electron beam selective melting, and shaping a three-dimensional model of the 24CrNiMo alloy steel:

[0056] The Materialise Magics software is used to sequentially construct a three-dimensional machining platform and a machining part, the size of the machining part is x=15 mm, y=15 mm, and z=10 mm, the SL-EBM BuildPrepare software is used for slice processing of the three-dimensional model of the machining part to obtain data, the data is subjected to path planning to form an STL format file, and the STL format file is imported into an electron beam selective melting device;

[0057] S3, electron beam selective melting printing 24CrNiMo alloy steel:

[0058] The printing process parameters of the electron beam selective melting equipment are set, and the substrate leveling and powder filling of the forming bin in the electron beam selective melting equipment are performed; the printing process parameters are: power current is 10 mA, scanning speed is 5 m / s, powder taking amount is 0.10 mm, pre-powder thickness is 50 μm, beam spot defocusing amount is-0.500 V, and beam spot size is 0.100 mm;

[0059] The powder bed chamber of the electron beam selective melting equipment is subjected to vacuumizing treatment, the rotation speed of the vacuum pump is 60000 r / min, the rotation speed of the electron gun molecular pump is 72000 r / min, and when the vacuum degree reaches 7.5×10 -1 The protection gas is filled, filled for 2-3 min, and then the high-voltage power supply is turned on to 60 KV, and after the high voltage is stable, the electron beam is centered;

[0060] The substrate preheating is turned on again, and the substrate preheating is divided into three stages: the first stage is preheated to 100℃ with a current of 5 mA, then preheated to 250℃ with a current of 10 mA and kept for 8 min; the second stage is preheated to 600℃ with a current of 15 mA and kept for 8 min; the third stage is preheated to 850℃ with a current of 20 mA and kept for 8 min;

[0061] The current and scanning speed are adjusted, after the substrate preheating is completed, the powder bed preheating is performed, the maximum current of the powder bed preheating is 48.0 mA, the average current of the powder bed preheating is 14.00 mA, the minimum time of the powder bed preheating is 13.00 s, the maximum time of the powder bed preheating is 20.00 s, and the total preheating time of the powder bed preheating is 33.00 s;

[0062] After the powder bed preheating is completed, the printing is started, and the 24CrNiMo alloy steel is obtained.

[0063] Example 2

[0064] The difference between this embodiment and example 1 is that in step S1, the raw material of the 24CrNiMo alloy steel powder is: C: 0.20%, Cr: 0.95%, Ni: 0.95%, Si: 0.2%, Mo: 0.4%, Mn: 0.6%, and the balance is Fe element.

[0065] Example 3

[0066] The difference between this embodiment and example 1 is that in step S1, the raw material of the 24CrNiMo alloy steel powder is: C: 0.25%, Cr: 1.2%, Ni: 1.25%, Si: 0.4%, Mo: 0.8%, Mn: 1.2%, and the balance is Fe element.

[0067] Example 4

[0068] The difference between this example and Example 1 is that in step S1-1: the melting temperature is 1600℃, and the melting time is 55 min.

[0069] Example 5

[0070] The difference between this example and Example 1 is that in step S1-1: the melting temperature is 1650℃, and the melting time is 65 min.

[0071] Example 6

[0072] The difference between this example and Example 1 is that in step S1-2: the molten metal is connected to the atomizing nozzle and flows out at a speed of 7 kg / min, and meets the high-speed airflow at the atomizing nozzle, and the air pressure of the high-speed airflow is 3.5 MPa, to obtain the alloy powder.

[0073] Example 7

[0074] The difference between this example and Example 1 is that in step S1-2: the molten metal is connected to the atomizing nozzle and flows out at a speed of 9 kg / min, and meets the high-speed airflow at the atomizing nozzle, and the air pressure of the high-speed airflow is 4.5 MPa, to obtain the alloy powder.

[0075] Example 8

[0076] The difference between this example and Example 1 is that in step S1-3: the 24CrNiMo alloy steel powder is placed in a drying box at 115℃ for drying.

[0077] Example 9

[0078] The difference between this example and Example 1 is that in step S1-3: the 24CrNiMo alloy steel powder is placed in a drying box at 125℃ for drying.

[0079] Example 10

[0080] The difference between this example and Example 1 is that in step S1, the drying treatment temperature is 60℃, and the time is 20 min.

[0081] Example 11

[0082] The difference between this example and Example 1 is that in step S1, the drying treatment temperature is 80℃, and the time is 40 min.

[0083] Example 12

[0084] The difference between this embodiment and embodiment 1 is that in step S3, the printing process parameters are: power current is 6 mA, scanning speed is 3.5 m / s, powder taking amount is 0.09 mm, pre-powder thickness is 50 μm, beam spot defocusing amount is -0.500 V, and beam spot size is 0.100 mm.

[0085] Embodiment 13

[0086] The difference between this embodiment and embodiment 1 is that in step S3, the printing process parameters are: power current is 16 mA, scanning speed is 6.5 m / s, powder taking amount is 0.12 mm, pre-powder thickness is 50 μm, beam spot defocusing amount is -0.500 V, and beam spot size is 0.100 mm.

[0087] Embodiment 14

[0088] The difference between this embodiment and embodiment 1 is that in step S3, the substrate preheating is divided into three stages: after preheating to 100℃ at 5 mA, the current is changed to 10 mA to preheat to 240℃ and keep for 5 min; in the second stage, the current is changed to 15 mA to preheat to 590℃ and keep for 5 min; in the third stage, the current is changed to 20 mA to preheat to 840℃ and keep for 5 min.

[0089] Embodiment 15

[0090] The difference between this embodiment and embodiment 1 is that in step S3, the substrate preheating is divided into three stages: after preheating to 100℃ at 5 mA, the current is changed to 10 mA to preheat to 260℃ and keep for 10 min; in the second stage, the current is changed to 15 mA to preheat to 610℃ and keep for 10 min; in the third stage, the current is changed to 20 mA to preheat to 860℃ and keep for 10 min.

[0091] Embodiment 16

[0092] The difference between this embodiment and embodiment 1 is that the maximum current of the powder bed preheating is 48.0 mA, the average current of the powder bed preheating is 12.00 mA, the minimum time of the powder bed preheating is 8.00 s, the maximum time of the powder bed preheating is 16.00 s, and the total preheating time of the powder bed preheating is 24.00 s.

[0093] Embodiment 17

[0094] The difference between this embodiment and embodiment 1 is that the maximum current of the powder bed preheating is 48.0 mA, the average current of the powder bed preheating is 16.00 mA, the minimum time of the powder bed preheating is 18.00 s, the maximum time of the powder bed preheating is 25.00 s, and the total preheating time of the powder bed preheating is 43.00 s.

[0095] Embodiment 18

[0096] The difference between the embodiment and the embodiment 1 is that, in the step S1, the drying treatment is:

[0097] The 24CrNiMo alloy steel powder is first dehumidified at 110-120℃ for 18min, and a gas stream is sprayed to the 24CrNiMo alloy steel powder for dispersion treatment during the dehumidification process, the gas stream is hydrogen stream, and the spraying rate of the gas stream is 20mL / min;

[0098] The dehumidified 24CrNiMo alloy steel powder is then subjected to temperature-variable microwave drying to obtain the 24CrNiMo alloy steel powder after the drying treatment is completed.

[0099] The temperature-variable microwave drying is: first microwave drying at 145℃ for 4min, the microwave frequency is 665W; then microwave drying at 130℃ for 8min, the microwave frequency is 475W; finally microwave drying at 145℃ for 4min, the microwave frequency is 665W.

[0100] Embodiment 19

[0101] The difference between the embodiment and the embodiment 18 is that the 24CrNiMo alloy steel powder is first dehumidified at 110℃ for 15min.

[0102] Embodiment 20

[0103] The difference between the embodiment and the embodiment 18 is that the 24CrNiMo alloy steel powder is first dehumidified at 120℃ for 20min.

[0104] Embodiment 21

[0105] The difference between the embodiment and the embodiment 18 is that the spraying rate of the gas stream is 15mL / min.

[0106] Embodiment 22

[0107] The difference between the embodiment and the embodiment 18 is that the spraying rate of the gas stream is 25mL / min.

[0108] Embodiment 23

[0109] The difference between the embodiment and the embodiment 18 is that the temperature-variable microwave drying is: first microwave drying at 140℃ for 3min, the microwave frequency is 650W; then microwave drying at 135℃ for 5min, the microwave frequency is 500W; finally microwave drying at 140℃ for 3min, the microwave frequency is 650W.

[0110] Embodiment 24

[0111] The difference between the embodiment and the embodiment 18 is that the temperature-variable microwave drying is: first microwave drying at 150 DEG C for 5 min, the microwave frequency is 680 W; then microwave drying at 125 DEG C for 10 min, the microwave frequency is 500 W; finally microwave drying at 150 DEG C for 5 min, the microwave frequency is 680 W.

[0112] Experimental example

[0113] From Figure 1 It can be seen that the surface quality and forming quality of the 24CrNiMo alloy steel prepared by the method are excellent. Figure 2 It can be seen that the 24CrNiMo powder is relatively flat and the particle size is relatively uniform. Figure 3 And Figure 4 It can be seen that the microstructure of the 24CrNiMo alloy steel is mainly composed of GB granular bainite and BM partial bainite, the bainite has good strength and toughness, and the two kinds of bainite structures are uniformly distributed.

[0114] For the 24CrNiMo alloy steel prepared in each embodiment, 5 sample pieces of each embodiment are taken to test the performance of the 24CrNiMo alloy steel, and the average value of the score measurement results of the 5 sample pieces of each embodiment is taken as the score measurement result of the embodiment.

[0115] 1. The effect of the raw material ratio of the 24CrNiMo alloy steel on the hardness and density of the 24CrNiMo alloy steel.

[0116] Table 1 hardness (HV) and density (%) of 24CrNiMo alloy steel in examples 1-3

[0117] Group Example 1 Example 2 Example 3 Hardness 458 408 404 Density 98.0 94.7 94.2

[0118] From the results in Table 1, it can be seen that the hardness and density of the 24CrNiMo alloy steel will be reduced when the proportion of Fe element is too small or too large, and the raw material ratio in example 1 is relatively optimal.

[0119] 2. The effect of each step parameter of preparing 24CrNiMo alloy steel powder on the hardness and density of 24CrNiMo alloy steel.

[0120] Table 2 hardness (HV) and density (%) of 24CrNiMo alloy steel in examples 4-11

[0121]

[0122] As can be seen from Table 2, when preparing the 24CrNiMo alloy steel powder, the smelting temperature is too low or too high, the gas atomization parameters are too small or too large, the vacuum drying temperature is too low or too high, and the drying treatment parameters are too small or too large, which will reduce the hardness and density of the 24CrNiMo alloy steel, so by comparing Table 1 and Table 2, the parameters of Example 1 are relatively more optimal.

[0123] Table 3 Hardness (HV) and density (%) of 24CrNiMo alloy steel in Examples 18-24

[0124]

[0125] As can be seen from Table 3, the powder is dispersed at low temperature and dehumidified, and then subjected to variable temperature microwave drying, which slightly improves the hardness and density of the 24CrNiMo alloy steel, and also makes the hardness and density more stable under different parameter conditions, thereby improving the preparation efficiency;

[0126] As can be seen from Table 3, the powder is dispersed at low temperature and dehumidified, and then subjected to variable temperature microwave drying, which slightly improves the hardness and density of the 24CrNiMo alloy steel, and also makes the hardness and density more stable under different parameter conditions, thereby improving the preparation efficiency;

[0127] 3. The effect of each step parameter of printing 24CrNiMo alloy steel on the hardness and density of 24CrNiMo alloy steel.

[0128] Table 4 Hardness (HV) and density (%) of 24CrNiMo alloy steel in Examples 12-17

[0129]

[0130] As can be seen from Table 4, the printing process parameters are too small or too large, the substrate preheating parameters are too small or too large, and the powder bed preheating parameters are too small or too large, which will reduce the hardness and density of the 24CrNiMo alloy steel, so by comparing Table 1 and Table 2, the effect of Example 1 is relatively more optimal.

Claims

1. A method of producing a 24CrNiMo alloy steel, characterized in that, The method comprises the following steps: S1, preparation of 24CrNiMo alloy steel powder and pretreatment before printing: The 24CrNiMo alloy steel powder with a particle size of 50-120 μm is prepared by using a gas atomization method, and the raw material of the 24CrNiMo alloy steel powder comprises, by mass percentage, C: 0.20-0.25%, Cr: 0.95-1.2%, Ni: 0.95-1.25%, Si: 0.2-0.4%, Mo: 0.4-0.8%, Mn: 0.6-1.2%, and the balance of Fe; Then, the 24CrNiMo alloy steel powder is dried; the drying treatment is as follows: First, the 24CrNiMo alloy steel powder is dehumidified at 110-120°C for 15-20 min, and a gas stream is sprayed on the 24CrNiMo alloy steel powder for dispersion treatment during the dehumidification process, the gas stream is a hydrogen stream, and the spraying rate of the gas stream is 15-25 mL / min; Then, the 24CrNiMo alloy steel powder after the dehumidification treatment is subjected to microwave drying at variable temperatures to obtain the 24CrNiMo alloy steel powder after the drying treatment; The microwave drying at variable temperatures is as follows: first, microwave drying at 140-150°C for 3-5 min, microwave frequency is 650-680 W; then, microwave drying at 125-135°C for 5-10 min, microwave frequency is 450-500 W; finally, microwave drying at 140-150°C for 3-5 min, microwave frequency is 650-680 W; S2, construction of electron beam selective melting, and forming of a three-dimensional model of the 24CrNiMo alloy steel: A three-dimensional machining platform and a machining part are sequentially constructed, the machining part has a size of x=15 mm, y=15 mm, and z=10 mm, the machining part is subjected to slice processing of the three-dimensional model to obtain data, the data is subjected to path planning to form an STL format file, and the STL format file is imported into an electron beam selective melting device; S3, electron beam selective melting printing of the 24CrNiMo alloy steel: According to the STL format file, printing process parameters of the electron beam selective melting equipment are set, and substrate leveling and powder filling are performed on the forming bin in the electron beam selective melting equipment; the powder bed chamber of the electron beam selective melting equipment is subjected to vacuumizing treatment, when the vacuum degree reaches 7.5×10 -1 After the protection gas is filled, 2-3 min is filled, and the high-voltage power supply is started to 60kV, and the electron beam is centered after the high-voltage is stable; Then, the substrate preheating is started, and the current and the scanning speed are adjusted, after the substrate preheating is completed, the powder bed preheating is started, after the powder bed preheating is completed, the printing is started, and the 24CrNiMo alloy steel is obtained.

2. The method of producing 24CrNiMo alloy steel according to claim 1, characterized by, In step S1, the 24CrNiMo alloy steel powder is prepared by using a gas atomization method as follows: S1-1: The raw material of the 24CrNiMo alloy steel is added into an electromagnetic induction furnace according to a proportioning ratio for smelting, the smelting temperature is 1600-1650°C, the smelting time is 55-65 min, argon gas is used for protection, and a metal liquid is obtained after the smelting is completed; S1-2: The metal liquid is connected to an atomization nozzle, and flows out at a speed of 7-9 kg / min, and meets a high-speed gas stream at the atomization nozzle, the gas pressure of the high-speed gas stream is 3.5-4.5 MPa, and an alloy powder is obtained; S1-3: The alloy powder is sieved to obtain the 24CrNiMo alloy steel powder, and is placed in a drying box at 115-125°C for drying.

3. The method of claim 1, wherein the 24CrNiMo alloy steel is prepared by the steps of: In step S3, the printing process parameters are: power current 6-16 mA, scanning speed 3.5-6.5 m / s, powder taking amount 0.09-0.12 mm, pre-powder thickness 50 μm, beam spot defocusing amount-0.500 V, and beam spot size 0.100 mm. ​ 4. The method of producing 24CrNiMo alloy steel according to claim 1, characterized in that, In step S3, during the vacuumizing process, the rotation speed of the vacuum pump is 60000 r / min, and the rotation speed of the electron gun molecular pump is 72000 r / min.

5. The method of claim 1, wherein the 24CrNiMo alloy steel is prepared by the steps of: In step S3, the substrate preheating is divided into three stages: in the first stage, the substrate is preheated to 100℃ at a current of 5 mA, then preheated to 240-260℃ at a current of 10 mA and kept for 5-10 min; in the second stage, the substrate is preheated to 590-610℃ at a current of 15 mA and kept for 5-10 min; in the third stage, the substrate is preheated to 840-860℃ at a current of 20 mA and kept for 5-10 min. ​ 6. The method of producing 24CrNiMo alloy steel according to claim 1, characterized in that, In step S3, the maximum current for the powder bed preheating is 48.0 mA, the average current for the powder bed preheating is 12.00-16.00 mA, the minimum time for the powder bed preheating is 8.00-18.00 s, the maximum time for the powder bed preheating is 16.00-25.00 s, and the total preheating time for the powder bed preheating is ≥ the minimum preheating time + the maximum preheating time.

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