Method for preparing superhard high-strength M42 high-speed steel through electron beam powder bed melting

Abstract

The invention relates to the technical field of additive manufacturing of high-speed steel, in particular to a method for preparing superhard high-strength M42 high-speed steel through electron beam powder bed melting. According to the method, the defect problem caused by powder splashing in the printing process can be effectively avoided, so that the porosity of a formed part is reduced, the density of a sample is improved, the M42 high-speed steel formed through additive manufacturing through the method is free of cracks, high in density, good in surface quality and uniform in structure, and separation of intracrystalline nano-micron carbide can be increased.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing of high-speed steel, and in particular to a method for preparing ultra-hard and high-strength M42 high-speed steel by electron beam powder bed melting. Background Art

[0002] As an important part of industrial machine tools, the development level of cutting tools directly determines the core competitiveness of the manufacturing industry. High-speed steel (HSS) has the advantages of high hardness and high wear resistance, and is an important material for manufacturing cutting tools.

[0003] M42 (W2Mo9Cr4VCo8) is a representative of high performance among high-speed steels due to its high carbon (1-1.15wt.%) and high alloy (>20wt.%) characteristics. However, due to the slow cooling rate, the cast structure of traditional cast M42 steel is prone to form segregation characterized by coarse and network eutectic carbides, which not only makes the subsequent forging and rolling hot processing processes difficult, but also significantly damages the mechanical properties.

[0004] Additive manufacturing technology is based on the principle of "discrete-accumulation" and manufactures physical parts in a point-by-point / line-by-line / layer-by-layer accumulation manner. Electron beam powder bed fusion is a technology that has developed rapidly in recent years. Due to its small molten pool (0.2mm~1mm), high cooling rate (10 6 Ks -1 ~10 8 Ks -1 ) characteristics can effectively regulate its organization to obtain excellent performance. At the same time, high energy density, high efficiency, and vacuum melting without impurities can produce high-performance M42 high-speed steel. However, the existing methods are prone to defects due to powder splashing during the printing process, resulting in increased porosity and uneven organization of the specimen. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned prior art, the object of the present invention is to provide a method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion. The present invention strengthens the powder bed through unique powder bed strengthening and thermal compensation before and after powder spreading. The whole process is in a vacuum environment and helium is continuously filled with protective gas to eliminate interference from harmful elements such as oxygen / nitrogen. The electron beam powder bed fusion printing process parameters are regulated to obtain M42 high-speed steel with excellent performance that does not require subsequent heat treatment. At the same time, residual stress is reduced through a high preheating temperature to obtain M42 high-speed steel with excellent performance / good quality.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing ultra-hard and high-strength M42 high-speed steel by electron beam powder bed melting comprises the following steps:

[0008] M42 steel powder is prepared by gas atomization and pre-treated before printing to obtain pre-treated M42 steel powder;

[0009] A three-dimensional model of M42 steel was constructed, sliced ​​along the height direction, and scanning parameters were set to obtain slice scanning data, which were then imported into the electron beam powder bed melting equipment.

[0010] The pretreated M42 steel powder is spread flat on the powder bed on the substrate, thermal compensation is performed before spreading the powder, and the powder bed is strengthened after spreading the powder. Under a protective atmosphere, when the preheating temperature of the substrate reaches 820℃~850℃, the pretreated M42 steel powder is melted, formed and printed layer by layer using an electron beam to obtain ultra-hard and high-strength M42 high-speed steel.

[0011] The present invention uses an electron beam as a heat source, and adopts powder bed reinforcement and thermal compensation before and after powder spreading to reinforce the powder bed during the additive manufacturing process of M42 high-speed steel, and adjusts the electron beam powder bed melting printing process parameters to obtain excellent performance M42 high-speed steel without subsequent heat treatment. At the same time, the residual stress is reduced by a high preheating temperature to obtain M42 high-speed steel with excellent performance / good quality. This method can effectively avoid defects caused by powder splashing during the printing process, thereby reducing the porosity of the formed part, improving the density of the sample, and making the organization more uniform.

[0012] In a preferred embodiment of the present invention, the powder in the forming area is reinforced for the second time by powder bed reinforcement, and the powder bed reinforcement parameters are: beam spot defocus 0V~0.5V, rated current 20mA~26mA, scanning speed 5m / s~8m / s, starting current 12mA~14mA, average current 14mA~16mA, current step increase: 3 levels, powder consolidation times 1~2 times.

[0013] In a preferred embodiment of the present invention, the electron beam current is 12 mA to 18 mA, the scanning speed is 5 m / s to 6.5 m / s, the beam spot diameter is 0.1 mm to 0.2 mm, the defocus amount is 0 V to 0.5 V, and the powder amount is 95 μm to 105 μm.

[0014] In a preferred embodiment of the present invention, the thermal compensation parameters before powder spreading are: beam spot defocus: 0V to 0.5V, rated current 10mA, time: 10s to 12s.

[0015] In a preferred embodiment of the present invention, the powder bed is preheated for micro-sintering after spreading the powder, and the sintering powder bed parameters are: scanning speed: 12m / s~14m / s, scanning spacing: 1mm~1.5mm, beam spot defocus: 0V~0.5V, rated current: 35mA, time: 10s~12s.

[0016] The powder bed is strengthened after printing and powder laying, and the powder bed is micro-sintered under a small preheating condition, thereby improving the conductivity of the powder bed and reducing the risks of "powder blowing" and "powder pushing" to improve the forming quality. Step preheating can reduce the impact of the electron beam on the powder bed, thereby reducing powder blowing during the printing process.

[0017] In a preferred embodiment of the present invention, the powder bed preheating method is step-up preheating, the preheating is divided into 3 levels, the preheating current is gradually increased, the maximum preheating current is 35mA to 40mA, and the starting current is 10mA to 12mA.

[0018] In a preferred embodiment of the present invention, the scanning mode is set to unidirectional scanning, and the scanning parameters are: the rotation angle between layers is 90°, the scanning interval is 80 μm, and the layer thickness is 50 μm.

[0019] Furthermore, the printing parameters were set, the powder amount was set to 95 μm to 105 μm, and the pre-powder thickness was 50 μm.

[0020] In a preferred embodiment of the present invention, after the M42 steel powder is loaded into the powder cylinder, vacuum is drawn until the vacuum degree of the gun chamber reaches 10 -3 After reaching the Pa level, the forming chamber is filled with helium protective atmosphere to ensure that the oxygen content of the air in the powder cylinder does not exceed 0.5%.

[0021] In a preferred embodiment of the present invention, the substrate is preheated manually, and the preheating temperature of the forming substrate is 820°C to 850°C.

[0022] The specific preheating is divided into three stages. The base plate is heated to 400℃, 700℃, and 850℃. The preheating current is 5mA~10mA and the scanning speed is 5m / s~10m / s to heat to 350℃~400℃. The preheating current is 15mA~20mA and the scanning speed is 10m / s~20m / s to heat to 600℃~700℃. The preheating current is 25mA~30mA and the scanning speed is 10m / s~20m / s to heat to 850℃ and keep warm for 5 minutes~10 minutes, 5 minutes~10 minutes, and 10 minutes~15 minutes respectively. The substrate material is 316L stainless steel substrate. Step-by-step heating is adopted during the preheating process. The current and scanning speed are gradually increased to make the substrate temperature rise steadily. In the insulation stage, the temperature rise is avoided too fast and the heating is uneven.

[0023] In a preferred embodiment of the present invention, the protective gas helium is continuously introduced during the entire printing process.

[0024] In a preferred embodiment of the present invention, the particle size of the M42 steel powder is 53μm to 120μm, and the composition of the M42 steel powder includes, by mass percentage: C: 1.05% to 1.15%, Cr: 3.50% to 4.25%, W: 1.15% to 1.85%, Mo: 9.0% to 10.0%, V: 0.95% to 1.35%, Co: 7.75% to 8.75%, Mn: ≤0.40%, Si: ≤0.65%, S: ≤0.03%, P: ≤0.03%, and the balance is Fe.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention uses an electron beam as a heat source, and adopts powder bed reinforcement and thermal compensation before and after powder laying to reinforce the powder bed in the additive manufacturing process of M42 high-speed steel, and adjusts the electron beam powder bed melting printing process parameters to obtain excellent performance M42 high-speed steel without subsequent heat treatment. At the same time, the residual stress is reduced by a high preheating temperature to obtain M42 high-speed steel with excellent performance / good quality. This method can effectively avoid defects caused by powder splashing during the printing process, thereby reducing the porosity of the formed part, improving the density of the sample, and making the organization more uniform.

[0027] 2. The M42 high-speed steel formed by additive manufacturing using the method of the present invention has no cracks, high density, good surface quality and uniform structure, and can increase the precipitation of nano-micrometer-level carbides in the crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a macroscopic image of M42 high-speed steel prepared by electron beam powder bed fusion in the present invention.

[0029] Figure 2 This is a surface quality diagram of M42 high-speed steel prepared by electron beam powder bed fusion in the present invention.

[0030] Figure 3 This is the SEM uniform structure diagram of the M42 high-speed steel prepared in Example 16 of the present invention. DETAILED DESCRIPTION

[0031] The following is a detailed description of the technical solutions in the embodiments of the present invention in combination with the preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be noted that all professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0033] Example 1

[0034] A method for preparing ultra-hard and high-strength M42 high-speed steel by electron beam powder bed melting comprises the following steps:

[0035] (1) M42 steel powder was prepared by gas atomization, and the powder particle size ranged from 53 μm to 120 μm. The powder components by mass percentage included: C: 1.05-1.15%, Cr: 3.50-4.25%, W: 1.15-1.85%, Mo: 9.0-10.0%, V: 0.95-1.35%, Co: 7.75-8.75%, Mn: ≤0.40%, Si: ≤0.65%, S: ≤0.03%, P: ≤0.03%, and the balance was Fe. The powder was pretreated before printing and dried in a vacuum drying oven at 80°C for 2 h to ensure that the powder had good fluidity. The powder was sieved with a 160-mesh sieve and collected for later use.

[0036] (2) A three-dimensional model of M42 steel was constructed and sliced ​​along the height direction. The construction size was 15 mm × 15 mm × 10 mm. The slicing software used was SL-EBM BuildPrepare. The scanning mode was set to unidirectional scanning, with each layer rotated 90° between layers, a scanning interval of 80 μm, and a layer thickness of 50 μm. The slice scanning data was obtained and imported into the electron beam powder bed melting equipment.

[0037] (3) Preparation of M42 high-speed steel by electron beam powder bed fusion

[0038] Thermal compensation was performed before powder spreading, and the thermal compensation parameters were: beam defocus: 0.2V, rated current 10mA, time: 11s. After powder spreading, the powder bed was strengthened. First, the powder bed was micro-sintered. The micro-sintering powder bed parameters were: scanning speed: 13.6m / s, scanning spacing: 1mm, beam defocus: 0.2V, rated current: 35mA, time: 11s. The powder in the forming area was then reinforced for the second time through powder bed reinforcement. The powder bed reinforcement parameters were: electron beam current 15mA, rated current 26mA, scanning speed 8m / s, starting current 16mA, current step increase: 3 levels, beam defocus 0.2V, and powder solidification times 1 time.

[0039] Put the dried powder into the powder cylinder of the forming chamber, level the forming area substrate, the substrate material is 316L stainless steel substrate, fill the M42 steel powder into the powder cylinder, and then draw the vacuum until the vacuum degree of the gun chamber reaches 10 -3 After the order of Pa, the forming chamber is filled with helium protective atmosphere to ensure that the oxygen content of the air in the powder cylinder does not exceed 0.5%. Then the substrate is preheated. The substrate preheating adopts manual preheating. The preheating forming substrate temperature is 850℃. The preheating adopts a step-by-step heating method. The substrate preheating is divided into three stages. Use a preheating current of 10mA and a scanning speed of 10m / s to heat to 400℃ and keep warm for 5 minutes, 18mA, 20m / s to heat to 700℃ and keep warm for 5 minutes, 25mA, 20m / s to heat to 850℃ and keep warm for 10 minutes. When the power supply voltage rises to 60kV, the forming chamber is vacuumed and filled with protective gas helium. When the preheated substrate reaches 850℃, printing begins. The electron beam scans according to the predetermined slicing trajectory. The printing parameters are: the electron beam current size is 18mA, the scanning speed is 5m / s, the beam spot diameter is 0.1mm, the defocus size is 0V, and the powder amount is 0.95mm.

[0040] The substrate is reduced by one powder bed layer thickness, thermal compensation is performed before powder spreading, powder is spread again, the powder bed is strengthened, and the scanning process is layered and stacked to obtain ultra-hard and high-strength M42 high-speed steel.

[0041] Example 2

[0042] The preparation method is the same as that in Example 1, except that the printing parameters are set as follows: the electron beam current is 12 mA, the scanning speed is 5 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0 V, and the powder amount is 1.05 mm.

[0043] Example 3

[0044] The preparation method is the same as that of Example 1, except that the printing parameters are set as follows: the electron beam current is 14 mA, the scanning speed is 5 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0 V, and the powder amount is 1.0 mm.

[0045] Example 4

[0046] The preparation method is the same as that of Example 1, except that the printing parameters are set as follows: the electron beam current is 16 mA, the scanning speed is 5 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0 V, and the powder amount is 0.95 mm.

[0047] Example 5

[0048] The preparation method is the same as that of Example 1, except that the printing parameters are set as follows: the electron beam current is 18 mA, the scanning speed is 5.5 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0.1 V, and the powder amount is 0.95 mm.

[0049] Example 6

[0050] The preparation method is the same as that of Example 1, except that the printing parameters are set as follows: the electron beam current is 18 mA, the scanning speed is 6 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0.2 V, and the powder amount is 0.95 mm.

[0051] Example 7

[0052] The preparation method is the same as that in Example 1, except that the printing parameters are set as follows: the electron beam current is 18 mA, the scanning speed is 6.5 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0.3 V, and the powder amount is 0.95 mm.

[0053] Example 8

[0054] The preparation method is the same as that of Example 1, except that the printing parameters are set as follows: the electron beam current is 18 mA, the scanning speed is 5 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0.1 V, and the powder amount is 0.95 mm.

[0055] Example 9

[0056] The preparation method is the same as that of Example 1, except that the printing parameters are set as follows: the electron beam current is 18 mA, the scanning speed is 5 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0.2 V, and the powder amount is 0.95 mm.

[0057] Example 10

[0058] The preparation method is the same as that in Example 1, except that the printing parameters are set as follows: the electron beam current is 18 mA, the scanning speed is 0.15 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0.3 V, and the powder amount is 0.95 mm.

[0059] Embodiment 11

[0060] The preparation method is the same as that of Example 1, except that the printing parameters are set as follows: the electron beam current is 18 mA, the scanning speed is 5 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0.4 V, and the powder amount is 0.95 mm.

[0061] Example 12

[0062] The preparation method is the same as that of Example 1, except that the printing parameters are set as follows: the electron beam current is 18 mA, the scanning speed is 5 m / s, the beam spot diameter is 0.1 mm, the defocus amount is 0.5 V, and the powder amount is 0.95 mm.

[0063] Embodiment 13

[0064] The preparation method is the same as that of Example 1, except that in the powder bed strengthening parameters: the number of powder solidification is 1 time, the electron beam current is 14 mA, and the beam spot defocus is 0.2V.

[0065] Embodiment 14

[0066] The preparation method is the same as that of Example 1, except that in the powder bed strengthening parameters: the number of powder solidification is 1 time, and the electron beam current is 15 mA.

[0067] Embodiment 15

[0068] The preparation method is the same as that of Example 1, except that in the powder bed strengthening parameters: the number of powder solidification is 1 time, and the electron beam current is 16 mA.

[0069] Example 16

[0070] The preparation method is the same as that of Example 1, except that in the powder bed strengthening parameters: the number of powder solidification is 2 times, and the electron beam current is 18 mA.

[0071] Embodiment 17

[0072] The preparation method is the same as that in Example 1, the only difference is that in the powder bed strengthening parameters: the beam spot defocus is 0.3V, the rated current is 20mA, the scanning speed is 5m / s, and the starting current is 12mA; in the printing parameters: the electron beam current is 12m / s, the scanning speed is 6.5m / s, the beam spot diameter is 0.2mm, the defocus amount is 3V, and the powder amount is 100μm; in the thermal compensation parameters before powder spreading: the beam spot defocus is 3V, and the time is 10s.

[0073] Embodiment 18

[0074] The preparation method is the same as that in Example 1, the only difference is that in the powder bed strengthening parameters: the beam spot defocus is 0.1V, the rated current is 22mA, the scanning speed is 7m / s, and the starting current is 13mA; in the printing parameters: the electron beam current is 15m / s, the scanning speed is 5.5m / s, the beam spot diameter is 0.15mm, the defocus size is 0.5V, and the powder amount is 105μm; in the thermal compensation parameters before powder spreading: the beam spot defocus is 5V, and the time is 12s.

[0075] Results Analysis

[0076] For the M42 high-speed steel prepared in the examples, the performance of each example was tested, and each sample was tested five times to take the average value. The results are as follows:

[0077] Table 1 Performance test results of Example 1-Example 6

[0078] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Density 99.6％ 98.5％ 98.9％ 99.2％ 99.1％ 99.2％ Hardness / HV 842.2 774.5 785.5 801.6 807.3 822.9

[0079] Table 2 Performance test results of Example 7-Example 11

[0080] Example 7 Example 8 Example 9 Example 10 Embodiment 11 Density 98.4％ 99.4％ 98.0％ 99.0％ 98.5％ Hardness / HV 785.7 821.7 763.1 801.4 779.5

[0081] Table 3 Performance test results of Example 12-Example 16

[0082] Example 12 Embodiment 13 Embodiment 14 Embodiment 15 Example 16 Density 99.0％ 99.3％ 99.2％ 99.1％ 99.5％ Hardness / HV 809.5 825.5 830.1 821.3 834.3

[0083] Tables 1 to 3 show the performance test results of M42 high-speed steel prepared in Example 1 to Example 16. It can be seen that the printing parameters have a significant effect on the molded samples. It can be seen from Samples 1 to 4 that when the scanning speed is constant, as the electron beam current increases, the density gradually increases. It can be seen from Samples 1, 5, 6, and 7 that when the electron beam current is constant, as the scanning speed increases, the defects such as pores and unfused in the sample gradually decrease, and the density increases significantly. This is because the scanning speed can adjust the solidification and melting speeds, and different scanning speeds mean different heat inputs, thereby changing the temperature and heat input of the molten pool.

[0084] At the same time, the quality of the powder bed during printing affects the organizational evolution and the final forming quality. Increasing the number of powder bed strengthening and powder consolidation can effectively enhance the stability of the powder bed, making the powders tightly bonded together, thereby reducing the risk of powder blowing caused by excessive electron beam energy, improving printing quality, and having higher density and better hardness.

[0085] Figure 1 This is a macroscopic image of M42 high-speed steel prepared by electron beam powder bed melting in the present invention. It can be seen from the image that the high-speed steel sample prepared by the method of the present invention has no obvious defects and has good forming quality.

[0086] Figure 2 This is a surface quality image of M42 high-speed steel prepared by electron beam powder bed fusion in the present invention. The surface quality of the sample is good and very smooth and clean, especially after powder bed strengthening, that is, the increase in the number of powder solidification times, the melting line on the surface can be clearly seen.

[0087] Figure 3This is the SEM uniform organization diagram of M42 high-speed steel prepared in Example 16 of the present invention. The parameters used are: electron beam current size 18mA, scanning speed 5m / s, defocusing size 0V, and powder consolidation times twice. It can be seen that a large amount of carbides are precipitated in the sample, which is a manifestation of its high hardness. At the same time, nano-micron-level fine carbides are evenly dispersed in the crystal, which helps to increase the toughness of the sample.

[0088] In summary, the present invention uses electron beam as the heat source, adopts powder bed reinforcement and thermal compensation before and after powder laying to reinforce the powder bed in the additive manufacturing process of M42 high-speed steel, and adjusts the electron beam powder bed melting printing process parameters to obtain excellent performance M42 high-speed steel without subsequent heat treatment. At the same time, the residual stress is reduced by high preheating temperature to obtain M42 high-speed steel with excellent performance / good quality. This method can effectively avoid defects caused by powder splashing during the printing process, thereby reducing the porosity of the formed part and improving the density of the sample.

[0089] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0090] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed melting, characterized in that: The following steps are involved: M42 steel powder is prepared by gas atomization and pre-treated before printing to obtain pre-treated M42 steel powder; Construct a 3D model of M42 steel, slice it along the height direction, set scanning parameters, obtain slice scanning data, and import the obtained slice scanning data into the electron beam powder bed fusion equipment; The pretreated M42 steel powder is spread flat on the powder bed on the substrate, thermal compensation is performed before spreading the powder, and the powder bed is strengthened after spreading the powder. Under a protective atmosphere, when the preheating temperature of the substrate reaches 820℃~850℃, the pretreated M42 steel powder is melted, formed and printed layer by layer using an electron beam to obtain ultra-hard and high-strength M42 high-speed steel.

2. The method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion according to claim 1, characterized in that: The powder bed strengthening parameters are: beam spot defocus 0V~0.5V, rated current 20mA~26mA, scanning speed 5m / s~8m / s, starting current 12mA~14mA, average current 14mA~16mA, current step increase: 3 levels, powder solidification times 1~2 times.

3. The method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion according to claim 1, characterized in that: The printing parameters are: electron beam current 12mA~18mA, scanning speed 5m / s~6.5m / s, beam spot diameter 0.1mm~0.2mm, defocus size 0V~0.5V, powder amount 95μm~105μm.

4. The method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion according to claim 1, characterized in that: The thermal compensation parameters before powder coating are: beam spot defocus: 0~0.5V, rated current 10mA, time: 10s~12s.

5. The method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion according to claim 1, characterized in that: After spreading the powder, the powder bed is preheated for sintering. The sintering powder bed parameters are: scanning speed 12m / s~14m / s, scanning spacing: 1mm~1.5mm, beam spot defocus: 0V~0.5V, rated current: 35mA, time: 10s~12s.

6. The method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion according to claim 1, characterized in that: The powder bed preheating method is step-up preheating. The preheating is divided into 3 levels, and the preheating current is gradually increased. The maximum preheating current is 35mA~40mA, and the starting current is 10mA~12mA.

7. The method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion according to claim 1, characterized in that: The scanning mode is unidirectional scanning, and the scanning parameters are: the rotation angle between layers is 90°, the scanning interval is 80μm, and the powder thickness is 50μm.

8. The method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion according to claim 1, characterized in that: The substrate is preheated manually, and the substrate preheating is divided into three stages: using a preheating current of 5mA~10mA and a scanning speed of 5m / s~10m / s to heat to 350℃~400℃, a preheating current of 15mA~20mA and a scanning speed of 10m / s~20m / s to heat to 600℃~700℃, and a preheating current of 25mA~30mA and a scanning speed of 10m / s~20m / s to heat to 850℃ and keep warm for 5 minutes to 10 minutes, 5 minutes to 10 minutes, and 10 minutes to 15 minutes respectively.

9. The method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion according to claim 1, characterized in that: The protective gas helium is continuously introduced during the entire printing process.

10. The method for preparing superhard and high-strength M42 high-speed steel by electron beam powder bed fusion according to claim 1, characterized in that: The particle size of M42 steel powder is 53μm~120μm, and the components of M42 steel powder include, by mass percentage: C: 1.05%~1.15%, Cr: 3.50%~4.25%, W: 1.15%~1.85%, Mo: 9.0%~10.0%, V: 0.95%~1.35%, Co: 7.75%~8.75%, Mn: ≤0.40%, Si: ≤0.65%, S: ≤0.03%, P: ≤0.03%, and the balance is Fe.

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