Additive-manufactured medium-carbon high-strength steel and preparation method thereof

Abstract

According to the medium-carbon high-strength steel for additive manufacturing and the preparation method of the medium-carbon high-strength steel, microstructure design is conducted by means of the characteristics of additive manufacturing, two kinds of alloy powder with different components are mechanically mixed to serve as initial powder before printing, and the medium-carbon high-strength steel without cracks can be obtained through additive manufacturing; through a proper tempering process, high strength can be obtained while good plasticity is kept, and the method is easy to operate and low in cost.

Description

Technical Field

[0001] This invention relates to a method for preparing medium-carbon high-strength steel by additive manufacturing, belonging to the field of additive manufacturing technology for steel structural materials. Background Technology

[0002] Traditional forged medium-carbon steel possesses high strength, hardness, and a certain degree of toughness, as well as strong corrosion resistance, making it widely used in structural materials for medical devices, aerospace, and mold making. However, it is difficult to produce high-strength medium-carbon steel with complex shapes using traditional methods. Additive manufacturing is suitable for producing parts with complex shapes, but high-strength medium-carbon steel has poor printability. Cracking is common after additive manufacturing. Although preheating the substrate can suppress printing cracking in medium-carbon steel, the mechanical properties after printing are poor, with typically low strength, plasticity, and toughness, making it difficult to obtain medium-carbon steel with good printability. Therefore, developing high-performance medium-carbon high-strength steel compositions and preparation processes suitable for additive manufacturing can promote the application of additive manufacturing technology in high-strength steel. Summary of the Invention

[0003] The present invention discloses an additively manufactured medium-carbon high-strength steel and its preparation method, which is achieved through the following technical solution: An additively manufactured medium-carbon high-strength steel is prepared by mechanically mixing two alloy powders of different compositions to obtain a mixed powder as the initial powder before additive manufacturing. Powder A has the following composition: 0.4~0.6% C, 1.5~2% Mo, 6.5~7.5% Cr, 1~2% W, 0.8~1.5% Si, 0.2~0.25% V, 0.05~0.1% Nb, 0.5~1% Al, with the remainder being Fe, all by weight percentage. Powder B has the following composition: 9~9.5% Ni, 14~15% Cr, 0.5~1% Al, 1~1.5% Mo, 1.5~2% Mn, with the remainder being Fe, all by weight percentage. The weight ratio of powder A to powder B is 7:1. Powder A has a particle size of 15~45μm, and powder B has a particle size of 45~53μm.

[0004] A method for preparing medium-carbon high-strength steel by additive manufacturing includes the following steps: Step (1): The alloy powder described in claim 1 is melted by laser powder bed to obtain a bulk material of the required shape and size. Then, the alloy part obtained by additive manufacturing is kept at liquid nitrogen for more than 30 minutes and then placed in a room temperature environment; Step (2): The part obtained in step (1) is tempered: after being kept at 550~580℃ for 2 hours, it is oil-cooled to room temperature, then kept at liquid nitrogen for more than 30 minutes and then placed in a room temperature environment. Finally, after being kept at 550℃ for 2 hours, it is air-cooled to room temperature to obtain high-strength steel. The outstanding substantive features and significant progress of the technical solution of the present invention are mainly reflected in the following: The present invention, targeting the technical characteristics of additive manufacturing, mixes two powders with different alloy compositions and different particle size distributions as the initial powder. One powder provides a medium-carbon martensite structure, and the other powder provides a tough blocky austenite structure. After laser printing, the main alloying elements and structure of the original powder can be retained. This method can suppress the generation of printing cracks. Furthermore, multiple cryogenic treatments combined with tempering can retain more stable tough austenite and form more dispersed precipitates, resulting in high yield strength. High mechanical properties can be achieved by embedding tough blocky austenite phases within a high-strength carbon-containing martensite structure. This method is simple to operate, low in cost, and suitable for industrial applications. Attached Figure Description

[0005] Figure 1 The microstructure of the high-strength steel in the printed state in Example 1.

[0006] Figure 2 The microstructure of the high-strength steel in the printed state in Example 2.

[0007] Figure 3 The microstructure of the high-strength steel in the printed state in Example 3.

[0008] Figure 4 The microstructure of the high-strength steel in the printed state in Example 4. Detailed Implementation

[0009] Example 1: A mixed powder obtained by mechanically mixing two alloy powders with different compositions was used as the initial powder before additive manufacturing. Powder A had the following composition: 0.4% C, 2% Mo, 7.5% Cr, 2% W, 1.5% Si, 0.25% V, 0.1% Nb, 1% Al, with the remainder being Fe, all by weight percentage. Powder B had the following composition: 9.5% Ni, 15% Cr, 1% Al, 1.5% Mo, 2% Mn, with the remainder being Fe, all by weight percentage. The alloy parts were obtained using laser powder bed melting, and their microstructure is as follows: Figure 1As shown, the matrix is ​​cellular martensite, and the arrow indicates the tough austenite phase. The parts are then held in liquid nitrogen for more than 30 minutes and then placed in a room temperature environment. The resulting parts are then tempered: held at 560℃ for 2 hours and then oil-cooled to room temperature, then held in liquid nitrogen for more than 30 minutes and then placed in a room temperature environment, and finally held at 550℃ for 2 hours and air-cooled to room temperature to obtain high-strength steel. The mechanical properties are shown in Table 1.

[0010] Example 2: A mixed powder obtained by mechanically mixing two alloy powders with different compositions was used as the initial powder before additive manufacturing. Powder A had the following composition: 0.5% C, 1.5% Mo, 6.5% Cr, 1% W, 0.8% Si, 0.2% V, 0.05% Nb, 0.5% Al, with the remainder being Fe, all by weight percentage. Powder B had the following composition: 9% Ni, 15% Cr, 1% Al, 1.5% Mo, 2% Mn, with the remainder being Fe, all by weight percentage. The alloy parts were obtained using laser powder bed melting, and their microstructure is as follows: Figure 2 As shown, the matrix is ​​cellular martensite, and the arrow indicates the tough austenite phase. The parts are then held in liquid nitrogen for more than 30 minutes and then placed in a room temperature environment. The resulting parts are then tempered: held at 550℃ for 2 hours and then oil-cooled to room temperature, then held in liquid nitrogen for more than 30 minutes and then placed in a room temperature environment, and finally held at 550℃ for 2 hours and air-cooled to room temperature to obtain high-strength steel. The mechanical properties are shown in Table 1.

[0011] Example 3: A mixed powder obtained by mechanically mixing two alloy powders with different compositions was used as the initial powder before additive manufacturing. Powder A had the following composition: 0.6% C, 1.5% Mo, 7.5% Cr, 1% W, 0.8% Si, 0.25% V, 0.1% Nb, 1% Al, with the remainder being Fe, all by weight percentage. Powder B had the following composition: 9% Ni, 15% Cr, 1% Al, 1.5% Mo, 2% Mn, with the remainder being Fe, all by weight percentage. The alloy parts were obtained using laser powder bed melting, and their microstructure is as follows: Figure 3 As shown, the matrix is ​​cellular martensite, and the arrow indicates the tough austenite phase. The parts are then held in liquid nitrogen for more than 30 minutes and then placed in a room temperature environment. The resulting parts are then tempered: held at 580℃ for 2 hours and then oil-cooled to room temperature, then held in liquid nitrogen for more than 30 minutes and then placed in a room temperature environment, and finally held at 550℃ for 2 hours and air-cooled to room temperature to obtain high-strength steel. The mechanical properties are shown in Table 1.

[0012] Example 4: A mixed powder obtained by mechanically mixing two alloy powders with different compositions was used as the initial powder before additive manufacturing. Powder A had the following composition: 0.55% C, 2% Mo, 6.5% Cr, 2% W, 0.8% Si, 0.25% V, 0.05% Nb, 1% Al, with the remainder being Fe, all by weight percentage. Powder B had the following composition: 9.5% Ni, 15% Cr, 1% Al, 1.5% Mo, 1.5% Mn, with the remainder being Fe, all by weight percentage. The alloy parts were obtained using laser powder bed melting, and their microstructure is as follows: Figure 4 As shown, the matrix is ​​cellular martensite, and the arrow indicates the tough austenite phase. The parts are then held in liquid nitrogen for more than 30 minutes and then placed in a room temperature environment. The resulting parts are then tempered: held at 580℃ for 2 hours and then oil-cooled to room temperature, then held in liquid nitrogen for more than 30 minutes and then placed in a room temperature environment, and finally held at 550℃ for 2 hours and air-cooled to room temperature to obtain high-strength steel. The mechanical properties are shown in Table 1. Table 1 Mechanical properties of the final alloys in Examples 1-4 Example Yield strength (MPa) Tensile strength (MPa) Elongation (%) Example 1 1635 2110 14 Example 2 1625 2105 13 Example 3 1720 2120 15 Example 4 1680 2100 15 Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An additively manufactured medium carbon high strength steel, characterized in that, The mixed powder obtained by mechanically mixing two different component alloy powders is used as the initial powder before additive manufacturing.

2. The additively manufactured medium carbon high strength steel of claim 1, wherein, The components of the powder A are: 0.4-0.6% C, 1.5-2% Mo, 6.5-7.5% Cr, 1-2% W, 0.8-1.5% Si, 0.2-0.25% V, 0.05-0.1% Nb, 0.5-1% Al, and the balance being Fe, all by weight. The components of the powder B are: 9-9.5% Ni, 14-15% Cr, 0.5-1% Al, 1-1.5% Mo, 1.5-2% Mn, and the balance being Fe, all by weight.

3. The additively manufactured medium carbon high strength steel of claim 1, wherein, The weight ratio of the powders A and B is 7:

1.

4. The additively manufactured medium carbon high strength steel of claim 1, wherein, The particle size of the powder A is 15-45 µm, and the particle size of the powder B is 45-53 µm.

5. The method for preparing medium-carbon high-strength steel by additive manufacturing according to claim 1, characterized in that, The method comprises the following steps: Step (1): the alloy powder of claim 1 is used to obtain a bulk material of a desired shape and size by laser powder bed melting, and then the alloy part obtained by additive manufacturing is kept in liquid nitrogen for more than 30 minutes, taken out and placed in a room temperature environment; Step (2): the part obtained in step (1) is tempered: kept at 550-580 ℃ for 2 hours, oil-cooled to room temperature, then kept in liquid nitrogen for more than 30 minutes, taken out and placed in a room temperature environment, finally kept at 550 ℃ for 2 hours, air-cooled to room temperature, and a high-strength steel is obtained.

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