Additive-manufactured high-hardness tool steel and preparation method thereof

Abstract

The invention discloses high-hardness tool steel for additive manufacturing and a preparation method of the high-hardness tool steel, initial powder of the high-hardness tool steel is formed by mechanically mixing alloy powder A and alloy powder B according to the mass ratio of 1: 2, and the alloy powder A comprises, by mass, 0.01%-0.02% of C, 2%-3% of W, 3%-4% of Cr, 1%-2% of V, 0.9%-1% of Ti and the balance Fe; and the alloy powder B comprises chemical components in percentage by mass as follows: 0.9%-1.2% of C, 30%-40% of Ni, 1%-2% of Mn, 1%-2% of Cu and the balance of Fe. The invention further specifically discloses a preparation method of the high-hardness tool steel for additive manufacturing. According to the method, a laser powder bed melting mode is adopted, the characteristics of a double-phase structure and uneven distribution of components are achieved through solidification behaviors of different alloy powder, and the crack-free high-hardness tool steel is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal additive manufacturing, and particularly relates to a high-hardness tool steel for additive manufacturing and a preparation method thereof. Background Art

[0002] Laser powder bed fusion can achieve the preparation of parts with high precision and complex shapes, and customized designs have been realized in various alloys. Tool steels with complex shapes and high carbon content have excellent performance and are in great demand in the manufacturing industry, with potential application value. By virtue of the characteristics of laser powder bed fusion technology, it is expected to obtain customized high-hardness tool steels with complex shapes. However, due to the high hardness of high-carbon tool steels and the large residual stress during the additive manufacturing process, it is difficult to obtain crack-free high-hardness tool steels, and additive manufacturing technology cannot be applied to high-hardness tool steels. Currently, there is no corresponding additive manufacturing process to achieve the preparation of crack-free high-carbon tool steels. Therefore, developing the composition of high-carbon tool steels suitable for additive manufacturing and additive manufacturing processes will promote the industrial application of additive manufacturing steel structural materials. Summary of the Invention

[0003] The technical problem solved by the present invention is to provide a high-hardness tool steel for additive manufacturing and a preparation method thereof. This method uses the method of laser powder bed fusion to achieve the characteristics of duplex structure and uneven composition distribution through the solidification behavior of different alloy powders, and obtains a crack-free high-hardness tool steel.

[0004] The present invention adopts the following technical solution to solve the above technical problem. A high-hardness tool steel for additive manufacturing is characterized in that: the initial powder of the high-hardness tool steel is mechanically mixed by alloy powder A and alloy powder B with a mass ratio of 1:2. The chemical composition and mass percentage content of alloy powder A are 0.01% - 0.02% C, 2% - 3% W, 3% - 4% Cr, 1% - 2% V, 0.9% - 1% Ti, and the balance is Fe; the chemical composition and mass percentage content of alloy powder B are 0.9% - 1.2% C, 30% - 40% Ni, 1% - 2% Mn, 1% - 2% Cu, and the balance is Fe.

[0005] Further, the particle size of the alloy powder A is 15 - 53 μm, and the particle size of the alloy powder B is 30 - 53 μm.

[0006] The preparation method of the high-hardness tool steel for additive manufacturing according to the present invention is characterized in that the specific steps are as follows: Step S1: Prepare alloy parts by using the above initial powder in the way of laser powder bed fusion; Step S2: Keep the alloy parts obtained in step S1 at 580 °C for 2 - 5 h and then air-cool to room temperature; Step S3: Take out the alloy part obtained in Step S2 after holding it at -70~-75°C for 1 h and place it in a room-temperature environment. Finally, hold it at 580°C for 2 h and then air-cool it to room temperature to obtain high-hardness tool steel.

[0007] Further, the process parameters of the laser powder bed melting in Step S1 are as follows: the laser power is 120~150 W, the scanning spacing is 70 μm, the powder layer thickness is 30 μm, the scanning speed is 1000~1100 mm / s, and after printing every 10~15 layers, stop for 8~10 s and then continue printing.

[0008] Compared with the prior art, the present invention has the following advantages and beneficial technologies: Through alloy composition design, by utilizing the differences in the melting and solidification behaviors of two alloy powders with different compositions, the present invention obtains the characteristics of a duplex structure (austenite and martensite) and non-uniform composition distribution, which can effectively avoid cracking during the additive manufacturing process. Then, alloy carbides (carbides containing Ti, V, Cr, and W) precipitate and further martensite transformation occurs during the subsequent heat treatment process, obtaining high hardness and toughness. Description of the Drawings

[0009] Figure 1 It is the microstructure photograph of the as-printed alloy part in Example 1; Figure 2 It is the microstructure photograph of the as-printed alloy part in Example 2; Figure 3 It is the microstructure photograph of the as-printed alloy part in Example 3. Detailed Embodiments

[0010] The following further elaborates on the above content of the present invention through examples, but it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. Any technology implemented based on the above content of the present invention belongs to the scope of the present invention. Example 1

[0011] Two kinds of powders with different compositions are respectively denoted as alloy powder A and alloy powder B. The chemical composition and mass percentage content of alloy powder A are: 0.01% C, 2% W, 3% Cr, 1% V, 0.9% Ti, and the balance is Fe. The chemical composition and mass percentage content of alloy powder B are: 0.9% C, 30% Ni, 1% Mn, 1% Cu, and the balance is Fe. The weight ratio of alloy powder A to alloy powder B in the mixed powder is 1:2. The particle size of alloy powder A is 15 - 53 μm, and the particle size of alloy powder B is 30 - 53 μm. An alloy part is obtained by laser powder bed melting. The process parameters of laser powder bed melting are: laser power is 120 W, scanning spacing is 70 μm, powder layer thickness is 30 μm, scanning speed is 1000 mm / s. After printing every 10 layers, stop for 8 seconds and then continue printing. The printed alloy part is annealed at 580 °C for 2 h and then air-cooled to room temperature. Then the alloy part is held at -70 °C for 1 h, taken out and placed in a room-temperature environment, and finally annealed at 580 °C for 2 h and then air-cooled to room temperature. The hardness of the finally obtained alloy part is shown in Table 1. The microstructure of the as-printed alloy part is as Figure 1 shown, which consists of austenite and acicular martensite. Austenite is a soft phase, which can inhibit the formation of printing cracks. After the first tempering, a large amount of carbides precipitate in the martensite, making the austenite carbon-depleted and its stability reduced. After cryogenic treatment, the austenite further transforms into a large amount of fresh martensite. After the second tempering, more carbides precipitate, obtaining a higher hardness. Example 2

[0012] Two kinds of powders with different compositions are respectively denoted as alloy powder A and alloy powder B. The chemical composition and mass percentage content of alloy powder A are: 0.02% C, 3% W, 4% Cr, 2% V, 1% Ti, and the balance is Fe. The chemical composition and mass percentage content of alloy powder B are: 1.2% C, 40% Ni, 2% Mn, 2% Cu, and the balance is Fe. The weight ratio of alloy powder A to alloy powder B in the mixed powder is 1:2. The particle size of alloy powder A is 15 - 53 μm, and the particle size of alloy powder B is 30 - 53 μm. An alloy part is obtained by laser powder bed melting. The process parameters of laser powder bed melting are: laser power is 150 W, scanning spacing is 70 μm, powder layer thickness is 30 μm, scanning speed is 1100 mm / s. After printing every 15 layers, stop for 10 seconds and then continue printing. The printed alloy part is annealed at 580 °C for 5 h and then air-cooled to room temperature. Then the alloy part is held at -75 °C for 1 h, taken out and placed in a room-temperature environment, and finally annealed at 580 °C for 2 h and then air-cooled to room temperature. The hardness of the finally obtained alloy part is shown in Table 1. The microstructure of the as-printed alloy part is as Figure 2As shown, it is composed of austenite and acicular martensite. Austenite is a soft phase that can inhibit the formation of printing cracks. After the first tempering, a large amount of carbides precipitate in the martensite, making the austenite carbon-depleted and reducing its stability. After cryogenic treatment, the austenite further transforms into a large amount of fresh martensite. After the second tempering, more carbides precipitate, obtaining a higher hardness. Example

[0013] Two powders with different compositions are respectively denoted as alloy powder A and alloy powder B. The chemical composition and mass percentage of alloy powder A are 0.02% C, 2.5% W, 3.5% Cr, 1.5% V, 0.95% Ti, and the balance is Fe. The chemical composition and mass percentage of alloy powder B are: 1% C, 35% Ni, 1.5% Mn, 1.5% Cu, and the balance is Fe. The weight ratio of alloy powder A to alloy powder B in the mixed powder is 1:2. The particle size of alloy powder A is 15 - 53 μm, and the particle size of alloy powder B is 30 - 53 μm. An alloy part is obtained by laser powder bed melting. The process parameters of laser powder bed melting are: laser power is 130 W, scanning spacing is 70 μm, powder layer thickness is 30 μm, scanning speed is 1000 mm / s. After printing every 12 layers, stop for 9 seconds and then continue printing. The printed alloy part is air-cooled to room temperature after holding at 580°C for 3 h, then taken out and placed in a room-temperature environment after holding at -72°C for 1 h, and finally air-cooled to room temperature after holding at 580°C for 2 h. The hardness of the finally obtained alloy part is shown in Table 1. The microstructure of the as-printed alloy part is as Figure 3 As shown, it is composed of austenite and acicular martensite. Austenite is a soft phase that can inhibit the formation of printing cracks. After the first tempering, a large amount of carbides precipitate in the martensite, making the austenite carbon-depleted and reducing its stability. After cryogenic treatment, the austenite further transforms into a large amount of fresh martensite. After the second tempering, more carbides precipitate, obtaining a higher hardness.

[0014] Table 1 Hardness of alloy parts in Examples 1 - 3

[0015] The above examples describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above examples. What is described in the above examples and the specification only illustrates the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A high-hardness tool steel for additive manufacturing, characterized in that: The initial powder of the high hardness tool steel is mechanically mixed by alloy powder A and alloy powder B in a mass ratio of 1:2, wherein the chemical composition and mass percentage of the alloy powder A are 0.01%~0.02% C, 2%~3% W, 3%~4% Cr, 1%~2% V, 0.9%~1% Ti, and the balance is Fe; the chemical composition and mass percentage of the alloy powder B are 0.9%~1.2% C, 30%~40% Ni, 1%~2% Mn, 1%~2% Cu, and the balance is Fe.

2. The high-hardness tool steel manufactured by additive manufacturing according to claim 1, characterized in that: The particle size of the alloy powder A is 15-53 μm, and the particle size of the alloy powder B is 30-53 μm.

3. A method for preparing high-hardness tool steel by additive manufacturing according to claim 1 or 2, characterized in that The specific steps are: Step S1: preparing alloy parts by laser powder bed melting of the initial powder; Step S2: keeping the alloy part obtained in step S1 at 580°C for 2-5 hours and then air-cooling it to room temperature; Step S3: The alloy parts obtained in step S2 are kept at -70~-75°C for 1 hour, then taken out and placed in a room temperature environment, and finally kept at 580°C for 2 hours and then air-cooled to room temperature to obtain high-hardness tool steel.

4. The method for preparing high-hardness tool steel by additive manufacturing according to claim 3, characterized in that: The process parameters of the laser powder bed melting in step S1 are as follows: laser power of 120-150 W, scanning spacing of 70 μm, powder layer thickness of 30 μm, scanning speed of 1000-1100 mm / s, and stopping for 8-10 seconds after printing every 10-15 layers before continuing printing.

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