High-strength steel based on laser powder bed melting and preparation method thereof

Abstract

The invention discloses high-strength steel based on laser powder bed melting and a preparation method of the high-strength steel. According to alloy designed through the method, martensite serves as a matrix, and high-density carbide in the matrix serves as a main strengthening phase. The two kinds of alloy powder are mixed, a solid solution alloy is obtained in a laser powder bed melting mode, high-yield-strength additive manufacturing steel can be finally achieved through a precipitated phase generated through follow-up tempering, and the method can be suitable for being applied to ultrahigh-strength steel under different service conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of metal additive manufacturing, and in particular to a high-strength steel based on laser powder bed melting and a preparation method thereof. Background Art

[0002] Ultra-high-strength steel prepared by traditional methods has excellent strength and toughness and is widely used in structural parts in the aerospace field. As the shape of parts becomes more complicated, it is difficult for ultra-high-strength steel prepared by traditional methods to obtain the desired shape through machining or plastic deformation. In addition, high-alloy steel materials prepared by traditional methods require high-temperature and long-term homogenization treatment to obtain alloys with uniform composition, which is costly and inefficient. At the same time, traditional casting processes limit the simultaneous addition of multiple alloy elements (easy to produce segregation and form coarse second phases). Metal additive manufacturing technology, especially laser powder bed melting technology, has the characteristics of rapid solidification, which can reduce element segregation to a more microscopic scale. At the same time, it has great potential in alloy composition design and preparation methods. However, it is difficult to obtain ultra-high yield strength through additive manufacturing, and the plasticity and toughness are also poor. There is still a lack of corresponding ideas and research on how to obtain high-strength materials through additive manufacturing technology. Therefore, new alloy design strategies and the development of suitable additive manufacturing processes are needed to prepare high-strength steel. Summary of the invention

[0003] The high-strength steel based on laser powder bed melting and the preparation method thereof of the present invention are realized by the following technical solutions: The present invention provides a high-strength steel based on laser powder bed melting, characterized in that the matrix of the high-strength steel is a martensite + austenite dual-phase structure, and the austenite content is 10% to 18%.

[0004] The present invention also provides the above-mentioned method for preparing high-strength steel based on laser powder bed melting, wherein two alloy powders A and B with different compositions are mechanically mixed to obtain a mixed powder, and the mixed powder is used as the initial powder before additive manufacturing of the high-strength steel. Both powders are obtained by argon atomization, and the purity of the argon is 99.99~99.999%; in terms of weight percentage, the composition of the powder A is: 0.5~0.6% C, 3~4% Mo, 8~10% Co, 9~10% Ni, 1~2% W and 0.5~1% Mn, and the rest is Fe; the composition of the powder B is: 8~10% Cr, 2~3% Ti, 1.5~2% Mn and 9~10% Ni, and the rest is Fe.

[0005] Further, the following steps are included: Step (1): two alloy powders A and B with different compositions are mechanically mixed to obtain a mixed powder, both powders are obtained by argon atomization, and the purity of the argon is 99.99-99.999%; The mixed powder is melted by laser powder bed to obtain parts of desired shape and size. No substrate heating is required during the printing process. After the printing process is completed, the substrate is heated to 200°C and kept warm for 60 minutes before stopping heating. After the substrate and parts are cooled to room temperature, they are taken out from the printing chamber together. Step (2): the alloy parts obtained by additive manufacturing are kept at -70°C to -75°C for more than 60 minutes, then taken out and placed in a room temperature environment; Step (3): Tempering the parts obtained in step (2): heat preservation at 420°C to 520°C for 8 to 10 hours and then air-cooling to room temperature, then heat preservation under liquid nitrogen for more than 30 minutes and then taking out and placing in room temperature environment, and finally heat preservation at 420°C to 520°C for 2 hours and then air-cooling to room temperature, so as to obtain the high-strength steel.

[0006] Furthermore, the diameter of powder A is 15 to 45 μm, and the diameter of powder B is 45 to 53 μm.

[0007] Furthermore, the weight ratio of powders A and B is 1:1.

[0008] Beneficial effects: The present invention aims at the technical characteristics of the laser powder bed. After mechanically mixing powders of two different alloy components, the powders are used as initial powders, which can avoid the formation of a large-sized second phase during the solidification process, so that an alloy of solid solution Ti and C can be obtained during the additive manufacturing process. Dispersed TiC can be precipitated during the subsequent tempering process to obtain higher strength. This method can achieve high-density carbides that are difficult to obtain using traditional casting methods. In addition, the two powders can be used to achieve parts with heterogeneous components and structures after laser printing, and ultimately an alloy with higher strength and toughness can be obtained. This method is simple to operate, low-cost, and suitable for industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a microstructure photograph of the high-strength steel in Example 1; Figure 2 is a microstructure photograph of the high-strength steel in Example 2; Figure 3 is a microstructure photograph of the high-strength steel in Example 3; Figure 4 This is a microstructure photograph of the high-strength steel in Example 4. DETAILED DESCRIPTION Example 1

[0010] Two powders A and B were obtained by gas atomization. The composition of powder A was 0.5% C, 3% Mo, 8% Co, 9% Ni, 1% W, 1% Mn, and the rest was Fe, all by weight. The composition of powder B was 8% Cr, 2% Ti, 1.5% Mn, 9% Ni, and the rest was Fe, all by weight. The diameter of powder A was 15~45μm, and the diameter of powder B was 45~53μm. The two powders A and B were mechanically mixed in a ratio of 1:1 and then melted by laser powder bed to obtain the block material of the required shape and size. No substrate heating was required during the printing process. After the printing program was completed, the substrate was heated to 200℃ and kept warm for 60 minutes, and then the heating was stopped. After the substrate and the parts were cooled to room temperature, they were taken out from the printing chamber together. Then the alloy parts were kept warm at -70℃ for more than 60 minutes and then taken out and placed in room temperature environment. The parts are then tempered. The specific process is: keep at 420℃ for 10 hours and then air cool to room temperature, then keep in liquid nitrogen for more than 30 minutes and then take out and put in room temperature environment, finally keep at 420℃ for 2 hours and air cool to room temperature, and high-strength steel can be obtained. The mechanical properties are shown in Table 1. The microstructure of the high-strength steel is as follows Figure 1 As shown, dispersed nano-precipitates are distributed inside the cellular structure. Example 2

[0011] Two powders A and B were obtained by gas atomization. The composition of powder A was 0.6% C, 4% Mo, 10% Co, 10% Ni, 2% W, 1% Mn, and the rest was Fe, all by weight. The composition of powder B was 10% Cr, 3% Ti, 2% Mn, 10% Ni, and the rest was Fe, all by weight. The diameter of powder A was 15~45μm, and the diameter of powder B was 45~53μm. The two powders A and B were mechanically mixed in a ratio of 1:1 and then melted by laser powder bed to obtain the block material of the required shape and size. No substrate heating was required during the printing process. After the printing program was completed, the substrate was heated to 200℃ and kept warm for 60 minutes, and then the heating was stopped. After the substrate and the parts were cooled to room temperature, they were taken out from the printing chamber together. Then the alloy parts were kept warm at -75℃ for more than 60 minutes and then taken out and placed in room temperature environment. The parts are then tempered. The specific process is: keep at 520℃ for 8 hours and then air cool to room temperature, then keep in liquid nitrogen for more than 30 minutes and then take out and put in room temperature environment, finally keep at 520℃ for 2 hours and then air cool to room temperature to obtain high-strength steel. The mechanical properties are shown in Table 1. The microstructure of the high-strength steel is as follows: Figure 2 As shown, dispersed nano-precipitates are distributed inside the cellular structure. Example 3

[0012] Two powders A and B were obtained by gas atomization. The composition of powder A was 0.55% C, 3.5% Mo, 9% Co, 10% Ni, 1.5% W, 1% Mn, and the rest was Fe, all by weight percentage. The composition of powder B was 9% Cr, 3% Ti, 2% Mn, 10% Ni, and the rest was Fe, all by weight percentage. The diameter of powder A was 15~45μm, and the diameter of powder B was 45~53μm. The two powders A and B were mechanically mixed in a ratio of 1:1 and then melted by laser powder bed to obtain the block material of the required shape and size. No substrate heating was required during the printing process. After the printing program was completed, the substrate was heated to 200℃ and kept warm for 60 minutes, and then the heating was stopped. After the substrate and the parts were cooled to room temperature, they were taken out from the printing chamber together. Then the alloy parts were kept warm at -70℃ for more than 60 minutes and then taken out and placed in room temperature environment. The parts are then tempered. The specific process is: keep at 500℃ for 10 hours and then air cool to room temperature, then keep in liquid nitrogen for more than 30 minutes and then take out and put in room temperature environment, finally keep at 420℃ for 2 hours and then air cool to room temperature to obtain high-strength steel. The mechanical properties are shown in Table 1. The microstructure of the high-strength steel is as follows Figure 3 As shown, dispersed nano-precipitates are distributed inside the cellular structure. Example 4

[0013] Two powders A and B were obtained by gas atomization. The composition of powder A was 0.5% C, 4% Mo, 8% Co, 10% Ni, 2% W, 1% Mn, and the rest was Fe, all by weight. The composition of powder B was 10% Cr, 2% Ti, 1.5% Mn, 10% Ni, and the rest was Fe, all by weight. The diameter of powder A was 15~45μm, and the diameter of powder B was 45~53μm. The two powders A and B were mechanically mixed in a ratio of 1:1 and then melted by laser powder bed to obtain the block material of the required shape and size. No substrate heating was required during the printing process. After the printing program was completed, the substrate was heated to 200℃ and kept warm for 60 minutes, and then the heating was stopped. After the substrate and the parts were cooled to room temperature, they were taken out from the printing chamber together. Then the alloy parts were kept warm at -73℃ for more than 60 minutes and then taken out and placed in room temperature environment. The parts are then tempered. The specific process is: keep at 480℃ for 10 hours and then air cool to room temperature, then keep in liquid nitrogen for more than 30 minutes and then take out and put in room temperature environment, and finally keep at 500℃ for 2 hours and air cool to room temperature to obtain high-strength steel. The mechanical properties are shown in Table 1. The microstructure of the high-strength steel is as follows Figure 4 As shown, dispersed nano-precipitates are distributed inside the cellular structure.

[0014] Table 1 Mechanical properties of the final alloys in Examples 1 to 4

Claims

1. A high-strength steel based on laser powder bed melting, characterized in that: The matrix of the high-strength steel is a dual-phase structure of martensite and austenite, and the austenite content is 10% to 18%.

2. A method for preparing high-strength steel based on laser powder bed melting as claimed in claim 1, characterized in that: Two alloy powders A and B with different compositions are mechanically mixed to obtain a mixed powder, which is used as the initial powder before additive manufacturing of the high-strength steel. Both powders are obtained by argon atomization, and the purity of argon is 99.99-99.999%. In terms of weight percentage, the composition of powder A is: 0.5-0.6% C, 3-4% Mo, 8-10% Co, 9-10% Ni, 1-2% W and 0.5-1% Mn, and the rest is Fe; the composition of powder B is: 8-10% Cr, 2-3% Ti, 1.5-2% Mn and 9-10% Ni, and the rest is Fe.

3. A method for preparing high-strength steel based on laser powder bed melting as claimed in claim 2, characterized in that: The following steps are involved: Step (1): two alloy powders A and B with different compositions are mechanically mixed to obtain a mixed powder, both powders are obtained by argon atomization, and the purity of the argon is 99.99-99.999%; The mixed powder is melted by laser powder bed to obtain parts of desired shape and size. No substrate heating is required during the printing process. After the printing process is completed, the substrate is heated to 200°C and kept warm for 60 minutes before stopping heating. After the substrate and parts are cooled to room temperature, they are taken out from the printing chamber together. Step (2): the alloy parts obtained by additive manufacturing are kept at -70°C to -75°C for more than 60 minutes, then taken out and placed in a room temperature environment; Step (3): Tempering the parts obtained in step (2): heat preservation at 420°C to 520°C for 8 to 10 hours and then air-cooling to room temperature, then heat preservation under liquid nitrogen for more than 30 minutes and then taking out and placing in room temperature environment, and finally heat preservation at 420°C to 520°C for 2 hours and then air-cooling to room temperature, so as to obtain the high-strength steel.

4. A method for preparing high-strength steel based on laser powder bed melting as claimed in claim 3, characterized in that: The diameter of powder A is 15~45μm, and the diameter of powder B is 45~53μm.

5. A method for preparing high-strength steel based on laser powder bed melting as claimed in claim 4, characterized in that: The weight ratio of powder A and powder B is 1:1.

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