A high-strength steel based on laser powder bed melting and a preparation method thereof

Abstract

The present invention discloses a high-strength steel based on laser powder bed melting and a preparation method thereof. The alloy designed by this method has a martensite matrix, and the high-density carbides in the matrix are the main strengthening phases. By mixing two alloy powders and obtaining a solid-solution alloy through laser powder bed melting, the precipitation phases generated during subsequent tempering can ultimately achieve an additive manufacturing steel with high yield strength, which can be applied to ultra-high-strength steels under different service conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of metal additive manufacturing, and particularly relates 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. With the complication of part shapes, it is difficult for ultra-high-strength steel prepared by traditional methods to obtain the required shape through machining or plastic deformation. Moreover, high-alloy steel materials prepared by traditional methods require high-temperature and long-time homogenization treatment to obtain an alloy with uniform composition, resulting in high costs and low efficiency. At the same time, traditional casting processes limit the simultaneous addition of multiple alloying 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 smaller 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. At the same time, 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 are needed and suitable additive manufacturing processes are developed to prepare high-strength steel. Summary of the Invention

[0003] A high-strength steel based on laser powder bed melting and a preparation method thereof according to the present invention are achieved through the following technical solutions:

[0004] 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 duplex structure, and the austenite content is 10% - 18%.

[0005] The present invention also provides a preparation method of the above-mentioned high-strength steel based on laser powder bed melting. 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%. By 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 balance is Fe; the composition of powder B is: 8 - 10%Cr, 2 - 3%Ti, 1.5 - 2%Mn, and 9 - 10%Ni, and the balance is Fe.

[0006] Further, it includes the following steps:

[0007] Step (1): Obtain a mixed powder by mechanically mixing alloy powders A and B with two different compositions. Both powders are obtained by argon atomization, and the purity of argon is 99.99 - 99.999%;

[0008] Obtain a part with the required shape and size from the above-mentioned mixed powder by laser powder bed melting. During the printing process, no substrate heating is required. After the printing program is completed, heat the substrate to 200 °C and keep it warm for 60 minutes, then stop heating. After the temperature of the substrate and the part cools down to room temperature, take them out together from the printing chamber;

[0009] Step (2): Take out the alloy part obtained by the above additive manufacturing after keeping it at -70 °C to -75 °C for more than 60 minutes and place it in a room-temperature environment;

[0010] Step (3): Temper the part obtained in step (2): Keep it at 420 °C to 520 °C for 8 - 10 hours and then air-cool it to room temperature. Then keep it in liquid nitrogen for more than 30 minutes and take it out to room temperature environment. Finally, keep it at 420 °C to 520 °C for 2 hours and then air-cool it to room temperature to obtain the high-strength steel.

[0011] Furthermore, the diameter of powder A is 15 - 45 μm, and the diameter of powder B is 45 - 53 μm.

[0012] Furthermore, the weight ratio of powder A and B is 1:1.

[0013] Beneficial effects: In view of the technical characteristics of the laser powder bed, the present invention mechanically mixes powders with two different alloy compositions as the initial powder, which can avoid the formation of large-sized second phases during solidification, enabling the acquisition of an alloy with solid-solved Ti and C during the additive manufacturing process. Dispersed TiC can precipitate during the subsequent tempering process, resulting in high strength. This method can achieve high-density carbides that are difficult to obtain by traditional casting methods. Additionally, after laser printing of the two powders, parts with compositional and microstructural heterogeneity can be achieved, ultimately obtaining an alloy with high strength and toughness. This method is simple to operate, low in cost, and suitable for industrial applications. Description of the Drawings

[0014] Figure 1 Microstructure photograph of the high-strength steel in Example 1;

[0015] Figure 2 Microstructure photograph of the high-strength steel in Example 2;

[0016] Figure 3 Microstructure photograph of the high-strength steel in Example 3;

[0017] Figure 4 Microstructure photograph of the high-strength steel in Example 4. Detailed Description of the Invention Example 1

[0018] Two kinds of powders, powder A and powder B, were obtained by gas atomization. The composition of powder A is: 0.5% C, 3% Mo, 8% Co, 9% Ni, 1% W, 1% Mn, and the rest is Fe, all in weight percentages. The composition of powder B is: 8% Cr, 2% Ti, 1.5% Mn, 9% Ni, and the rest is Fe, all in weight percentages. The diameter of powder A is 15 - 45 μm, and the diameter of powder B is 45 - 53 μm. After mechanically mixing powders A and B in a ratio of 1:1, a bulk material with the required shape and size was obtained by laser powder bed melting. During the printing process, no substrate heating was required. After the printing program was completed, the substrate was heated to 200 °C and held for 60 minutes, then the heating was stopped. After the temperature of the substrate and the part cooled to room temperature, they were taken out together from the printing chamber. Subsequently, the obtained alloy part was taken out after being held at -70 °C for more than 60 minutes and placed in a room temperature environment. Then the part was tempered. The specific process was: held at 420 °C for 10 hours and then air-cooled to room temperature, then held under liquid nitrogen for more than 30 minutes and taken out to room temperature environment, and finally held at 420 °C for 2 hours and air-cooled to room temperature. A high-strength steel could be obtained, and its mechanical properties are shown in Table 1. The microstructure of this high-strength steel is as Figure 1 shown, and dispersed nano-precipitates are distributed inside the cellular structure. Example 2

[0019] Two kinds of powders, powder A and powder B, were obtained by gas atomization. The composition of powder A is: 0.6% C, 4% Mo, 10% Co, 10% Ni, 2% W, 1% Mn, and the rest is Fe, all in weight percentages. The composition of powder B is: 10% Cr, 3% Ti, 2% Mn, 10% Ni, and the rest is Fe, all in weight percentages. The diameter of powder A is 15 - 45 μm, and the diameter of powder B is 45 - 53 μm. After mechanically mixing powders A and B in a ratio of 1:1, a bulk material with the required shape and size was obtained by laser powder bed melting. During the printing process, no substrate heating was required. After the printing program was completed, the substrate was heated to 200 °C and held for 60 minutes, then the heating was stopped. After the temperature of the substrate and the part cooled to room temperature, they were taken out together from the printing chamber. Subsequently, the obtained alloy part was taken out after being held at -75 °C for more than 60 minutes and placed in a room temperature environment. Then the part was tempered. The specific process was: held at 520 °C for 8 hours and then air-cooled to room temperature, then held under liquid nitrogen for more than 30 minutes and taken out to room temperature environment, and finally held at 520 °C for 2 hours and air-cooled to room temperature. A high-strength steel could be obtained, and its mechanical properties are shown in Table 1. The microstructure of this high-strength steel is as Figure 2 shown, and dispersed nano-precipitates are distributed inside the cellular structure. Example 3

[0020] Two powders, powder A and powder B, are obtained by gas atomization. The composition of powder A is: 0.55% C, 3.5% Mo, 9% Co, 10% Ni, 1.5% W, 1% Mn, and the balance is Fe, all in weight percentages. The composition of powder B is: 9% Cr, 3% Ti, 2% Mn, 10% Ni, and the balance is Fe, all in weight percentages. The diameter of powder A is 15 - 45 μm, and the diameter of powder B is 45 - 53 μm. Powders A and B are mechanically mixed in a 1:1 ratio and then a bulk material with the desired shape and size is obtained by laser powder bed melting. No substrate heating is required during the printing process. After the printing program is completed, the substrate is heated to 200 °C and held for 60 minutes, then the heating is stopped. After the temperature of the substrate and the part cools to room temperature, they are taken out together from the printing chamber. Subsequently, the obtained alloy part is taken out after being held at -70 °C for more than 60 minutes and placed in a room temperature environment. Then the part is tempered. The specific process is: held at 500 °C for 10 hours and then air-cooled to room temperature, then held under liquid nitrogen for more than 30 minutes and taken out to room temperature environment, and finally held at 420 °C for 2 hours and air-cooled to room temperature, and a high-strength steel can be obtained. The mechanical properties are shown in Table 1. The microstructure of this high-strength steel is as Figure 3 shown, and dispersed nano-precipitates are distributed inside the cellular structure. Example 4

[0021] Two powders, powder A and powder B, are obtained by gas atomization. The composition of powder A is: 0.5% C, 4% Mo, 8% Co, 10% Ni, 2% W, 1% Mn, and the balance is Fe, all in weight percentages. The composition of powder B is: 10% Cr, 2% Ti, 1.5% Mn, 10% Ni, and the balance is Fe, all in weight percentages. The diameter of powder A is 15 - 45 μm, and the diameter of powder B is 45 - 53 μm. Powders A and B are mechanically mixed in a 1:1 ratio and then a bulk material with the desired shape and size is obtained by laser powder bed melting. No substrate heating is required during the printing process. After the printing program is completed, the substrate is heated to 200 °C and held for 60 minutes, then the heating is stopped. After the temperature of the substrate and the part cools to room temperature, they are taken out together from the printing chamber. Subsequently, the obtained alloy part is taken out after being held at -73 °C for more than 60 minutes and placed in a room temperature environment. Then the part is tempered. The specific process is: held at 480 °C for 10 hours and then air-cooled to room temperature, then held under liquid nitrogen for more than 30 minutes and taken out to room temperature environment, and finally held at 500 °C for 2 hours and air-cooled to room temperature, and a high-strength steel can be obtained. The mechanical properties are shown in Table 1. The microstructure of this high-strength steel is as Figure 4 shown, and dispersed nano-precipitates are distributed inside the cellular structure.

[0022] Table 1 Mechanical properties of the final alloys in Examples 1 - 4

[0023]

Claims

1. A method for preparing 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 + austenite, and the austenite content is 10% to 18%; in terms of weight percentage, the composition of the powder A is: 0.5 to 0.6% C, 3 to 4% Mo, 8 to 10% Co, 9 to 10% Ni, 1 to 2% W and 0.5 to 1% Mn, and the rest is Fe; the composition of the powder B is: 8 to 10% Cr, 2 to 3% Ti, 1.5 to 2% Mn and 9 to 10% Ni, and the rest is Fe, specifically comprising the following steps: Step (1): mechanically mixing two alloy powders A and B of different compositions to obtain a mixed powder, and using the mixed powder as the initial powder for additive manufacturing of the high-strength steel, wherein the weight ratio of the powders A and B is 1:1, and 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.

2. A method for preparing high-strength steel based on laser powder bed melting as claimed in claim 1, characterized in that: The diameter of powder A is 15~45μm, and the diameter of powder B is 45~53μm.

3. A high-strength steel based on laser powder bed melting, characterized in that: The method is prepared according to claim 1 or 2.

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