Preparation method of heterostructure high-strength steel based on interlayer laser heat treatment

Abstract

The invention discloses a heterostructure high-strength steel preparation method based on interlayer laser heat treatment. The heterostructure high-strength steel preparation method comprises the following steps that the mapping relation between high-strength steel additive manufacturing process parameters and quenching and adjacent melt channel self-tempering area sizes is established; establishing a mapping relation between additive manufacturing high-strength steel interlayer laser heat treatment process parameters and quenching and tempering area sizes; determining microhardness change rules of quenching and tempering areas of the additive manufacturing high-strength steel under different post-forming heat treatment processes; different heterostructures are designed and prepared by regulating and controlling technological parameters of interlayer laser heat treatment and heat treatment after forming, so that the local mechanical property regulation and control requirements of the additive manufacturing high-strength steel are met. On the basis of interlayer in-situ laser heat treatment, the local microstructure and performance of the additive manufacturing high-strength steel are regulated and controlled, heat treatment after forming is combined, different performance matching and heterostructure preparation of structures are achieved, and flexible regulation and control of the mechanical performance of additive manufacturing high-strength steel parts in a three-dimensional space are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal additive manufacturing, and in particular to a method for preparing heterogeneous structural steel based on interlayer laser heat treatment. Background Art

[0002] Heterogeneous structural metal materials mainly use the non-uniform distribution of spatial structure, microstructure and even chemical composition to form "soft" and "hard" regions with different mechanical properties inside the material. During the deformation process, the "soft" and "hard" regions cooperate with plastic deformation to form heterogeneous induced strengthening, thereby improving the strength and plasticity of the material. Heterogeneous induced strengthening is not only an ideal method to break through the limits of the mechanical properties of metal materials, but also has the potential to meet the targeted improvement requirements of the mechanical properties of different regions of the same complex component through the matching of the performance, distribution form and proportion of the "soft" and "hard" regions.

[0003] In recent years, researchers at home and abroad have carried out a large number of studies on the preparation and performance of heterogeneous structural metal materials using one or several composite manufacturing methods such as heat treatment, surface mechanical grinding, asynchronous rolling, and additive manufacturing. Laser powder bed melting is currently the mainstream technology for additive manufacturing of complex metal components. Affected by the closed protective environment and powder bed in the additive manufacturing process, the introduction of heterogeneous induced strengthening effect in the laser powder bed melting additive manufacturing process is mainly based on online changes in forming process parameters. The heterogeneous structure is prepared through the quenching and self-tempering effects of the additive manufacturing process. The flexibility of heterogeneous structure preparation is poor, and the improvement and regulation of mechanical properties are limited.

[0004] High-strength steel is mainly used to manufacture key metal components such as molds, valves, gears, fasteners, etc., and has strict requirements on mechanical properties after forming. For the same component, high strength and hardness requirements are often seen for the main load-bearing parts and end faces, while excellent internal plasticity and toughness are of great significance to improving service life.

[0005] Based on this, the present invention proposes a method for preparing heterogeneous high-strength steel based on interlayer laser heat treatment, which aims to induce strengthening through heterogeneous deformation. On the one hand, the mechanical properties of additively manufactured high-strength steel are improved, and on the other hand, targeted regulation of the local mechanical properties of integrated formed complex components is carried out to meet the service requirements of additively manufactured high-strength steel in extremely complex service environments. Summary of the invention

[0006] In view of the problems of the prior art, the present invention provides a method for preparing heterogeneous high-strength steel based on interlayer laser heat treatment. The present invention is achieved through the following technical solutions:

[0007] A method for preparing heterogeneous structure high-strength steel based on interlayer laser heat treatment, comprising the following steps:

[0008] a. Establish the mapping relationship between the additive manufacturing process parameters of high-strength steel and the size of the quenching and adjacent melt channel self-tempering areas;

[0009] b. Establish the mapping relationship between the interlayer laser heat treatment process parameters of additively manufactured high-strength steel and the quenching and tempering area dimensions;

[0010] c. Clarify the variation law of microhardness in quenching and tempering areas of additively manufactured high-strength steel under different post-additive forming heat treatment processes;

[0011] d. By regulating the process parameters of interlayer laser heat treatment and post-additive forming heat treatment, heterogeneous structures of different types and matching performances are designed and prepared to meet the needs of local mechanical properties regulation of high-strength steel in additive manufacturing.

[0012] Preferably, the high-strength steel in step a is a high-strength steel material with a martensitic structure as the main component in an additive state, including tool steel, martensitic stainless steel, etc.

[0013] Preferably, the mapping relationship between the additive manufacturing process parameters and the quenching and adjacent melt channel self-tempering area sizes in step a and the mapping relationship between the interlayer laser heat treatment process parameters and the quenching and tempering area sizes in step b are obtained through temperature field simulation and process orthogonal experiments.

[0014] Preferably, the interlayer laser heat treatment in step b can adopt an additive manufacturing galvanometer processing system or a separate laser heat treatment galvanometer system, and the laser heat treatment spot adopts a beam shaping method to adopt a rectangular spot with adjustable width to reduce the non-uniform distribution of laser heat treatment energy of the Gaussian laser heat source.

[0015] Preferably, the spot width of the interlayer laser heat treatment in step b is 0.2-10 mm, the laser scanning rate is 5-500 mm / s, and the laser power is 300-5000 W, which meets the requirements of efficient preparation of heterogeneous structures of different sizes.

[0016] Preferably, the interlayer laser heat treatment in step b can be carried out every other layer or layers in the laser powder bed melting additive manufacturing process, and the interlayer heat treatment area can be the entire additive manufacturing surface or a local area of ​​the additive manufacturing surface, thereby meeting the needs of efficient preparation of different types of heterogeneous structures.

[0017] Preferably, the heat treatment process after additive manufacturing in step c is stress relief annealing or tempering. Due to the difference in the original organizational state, for the original quenching and tempering areas of additive manufacturing, under the same heat treatment conditions, the internal retained austenite content, dislocation density, and second phase precipitation behavior will have obvious differences, the heterogeneous structure will be preserved, and the performance matching of the "soft" and "hard" areas of the heterogeneous structure can be regulated by changing the heat treatment process after additive manufacturing.

[0018] Preferably, in step d, regulating the interlayer laser heat treatment process parameters includes changing the quenching and tempering areas in three-dimensional space by laser energy density, duty cycle, scanning line spacing, spot size, spot shape, etc. during the laser heat treatment process, and then further heat treating after forming to achieve controllable preparation of heterogeneous structures.

[0019] Preferably, the heterogeneous structure in step d includes any heterogeneous structure with matching "soft" and "hard" properties, such as point-shaped, strip-shaped, layered, etc. in three-dimensional space.

[0020] Preferably, the mechanical properties regulation in step d is mainly strength, hardness, wear resistance and two types of mechanical properties indicators, elongation and impact toughness, with the purpose of developing a targeted improvement method for mechanical properties based on heterogeneous structure regulation in the additive manufacturing process, laying the foundation for flexible regulation of mechanical properties in different three-dimensional spatial regions of high-strength steel components after final heat treatment.

[0021] The present invention is based on interlayer in-situ laser heat treatment to regulate the local microstructure and performance of additively manufactured high-strength steel, combined with post-forming heat treatment to achieve heterogeneous structure preparation with different performance matching and structure, and realize flexible regulation of the mechanical properties of additively manufactured high-strength steel parts in three-dimensional space. The beneficial technical effects of the present invention include:

[0022] (1) Laser heat treatment is a non-contact processing method with high processing flexibility and precision. It can be easily combined with the laser powder bed fusion additive manufacturing system. By adjusting the laser heat treatment process parameters between layers and combining the technical characteristics of layer-by-layer accumulation of additive manufacturing materials, various types of complex heterogeneous structures can be flexibly prepared in any area in three-dimensional space.

[0023] (2) Through the preparation of heterogeneous structures, not only can the mechanical properties of additively manufactured components be increased, but also targeted improvements can be achieved in local macro-regions, breaking through the limitations of traditional additive manufacturing integrated forming of complex components in mechanical properties regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The figure shows a schematic diagram of a process for preparing a heterogeneous structure high-strength steel based on interlayer laser heat treatment according to the present invention; Figure 2 Schematic diagram of powder bed laser melting of high-strength steel;

[0025] Figure 3 Schematic diagram of the mapping relationship between the interlayer laser heat treatment process parameters and the quenching and tempering area dimensions of the additively manufactured high-strength steel in Example 1;

[0026] Figure 4 Example 1 Schematic diagram of additively manufactured high-strength steel layered heterogeneous structure based on interlayer laser heat treatment;

[0027] Figure 5Example 1 Further control by heat treatment after forming Figure 4 Schematic diagram of mechanical property matching of medium-layered heterogeneous structures;

[0028] Figure 6 Schematic diagram of the mapping relationship between the interlayer laser heat treatment process parameters and the quenching and tempering area dimensions of the additively manufactured high-strength steel in Example 2;

[0029] Figure 7 Example 2 Schematic diagram of complex heterogeneous structure of additively manufactured high-strength steel based on interlayer laser heat treatment;

[0030] Figure 8 Example 2 Further control by heat treatment after forming Figure 7 Schematic diagram of mechanical properties matching of complex heterogeneous structures;

[0031] Figure numbers: 1-superficial additive manufacturing quenching area, 2-layer-by-layer additive interface, 3-superficial additive manufacturing self-tempering area, 4-interlayer laser heat treatment quenching area, 5-interlayer laser heat treatment tempering area, 6-interlayer laser heat treatment quenching area, 7-interlayer laser heat treatment tempering area. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are merely exemplary and can only be used to explain and illustrate the technical solution of the present invention, and cannot be interpreted as limiting the technical solution of the present invention.

[0033] The specific embodiments of the present invention are described in further detail below in conjunction with the accompanying drawings and examples. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0034] Embodiment 1:

[0035] This method for preparing heterogeneous high-strength steel based on interlayer laser heat treatment, the preparation process diagram is referenced Figure 1 , including the following steps:

[0036] Step 1: Carry out additive manufacturing of high-strength steel. Use ANSYS software to simulate the temperature field of laser additive manufacturing, and combine orthogonal experiments under different process conditions such as laser power and scanning rate. On the basis of ensuring the density of additive manufacturing, establish the mapping relationship between the additive manufacturing process parameters of high-strength steel and the size of the quenching and adjacent melt channel self-tempering area. Figure 2Schematic diagram of powder bed laser melting of high-strength steel. In the figure, area 1 is the quenching area of ​​the outermost additive manufacturing, 2 dotted lines are the layer-by-layer additive interface, and area 3 is the self-tempering area of ​​the outermost additive manufacturing. Since the sub-surface layer is also remelted during the outermost additive manufacturing, the self-tempering area is in the sub-surface layer.

[0037] Step 2: Conduct research on the interlayer laser heat treatment process for additive manufacturing of high-strength steel. Use ANSYS software to simulate the temperature field of laser heat treatment, and combine orthogonal experiments under different process conditions such as laser power, scanning rate, and defocus to establish a mapping relationship between the interlayer laser heat treatment process parameters for additive manufacturing of high-strength steel and the size of the quenching and tempering areas. Select appropriate laser heat treatment process parameters to prepare Figure 3 Interlayer laser heat treatment quenching and tempering areas. In the figure, area 4 is the interlayer laser heat treatment quenching area, and area 5 is the interlayer laser heat treatment tempering area.

[0038] Step 3: Conduct heat treatment of high-strength steel materials for additive manufacturing heterogeneous structures under different processes to clarify the influence of heat treatment after forming on the microhardness of tempering and quenching areas of heterogeneous structures. Figure 4 Since the dynamic processes of retained austenite transformation, carbide precipitation, dislocation recovery, etc. in the quenching and tempering areas during post-forming treatment are significantly different, the matching of mechanical properties of heterogeneous structures can be further regulated, and ultimately the preparation of heterogeneous structures with different matching "soft" and "hard" properties can be achieved.

[0039] Step 4: The high-strength steel is formed by the additive manufacturing process in step 1. In step 2, the interlayer laser heat treatment process is performed after each layer of material is added and on the entire surface area. After the additive forming, the tempering heat treatment is further performed to prepare the following Figure 5 Layered heterogeneous structure high strength steel.

[0040] Embodiment 2:

[0041] The method for preparing heterogeneous structure high-strength steel based on interlayer laser heat treatment comprises the following steps:

[0042] Step 1: Carry out additive manufacturing of high-strength steel. Through laser additive manufacturing temperature field simulation and orthogonal experiments under different laser power, scanning rate and other process conditions, establish the mapping relationship between high-strength steel additive manufacturing process parameters and the size of the quenching and adjacent melt channel self-tempering area. Figure 2 Schematic diagram of powder bed laser melting of high-strength steel. In the figure, area 1 is the quenching area of ​​the outermost additive manufacturing, 2 dotted lines are the layer-by-layer additive interface, and area 3 is the self-tempering area of ​​the outermost additive manufacturing. Since the sub-surface layer is also remelted during the outermost additive manufacturing, the self-tempering area is in the sub-surface layer.

[0043] Step 2: Compared with Example 1, the laser heat treatment temperature field simulation is carried out by ANSYS software, and the orthogonal experiment under different process conditions such as laser power, scanning rate, and defocusing amount is combined to establish the mapping relationship between the interlayer laser heat treatment process parameters of additive manufacturing high-strength steel and the quenching and tempering area size. Select appropriate laser heat treatment process parameters to prepare Figure 6 Interlayer laser heat treatment quenching and tempering areas, area 6 in the figure is the interlayer laser heat treatment quenching area, and area 7 is the interlayer laser heat treatment tempering area.

[0044] Step 3: Conduct heat treatment of high-strength steel materials for additive manufacturing heterogeneous structures under different processes to clarify the influence of heat treatment after forming on the microhardness of tempering and quenching areas of heterogeneous structures. Figure 7 , through conventional heat treatment after forming, the mechanical properties of the heterogeneous structure prepared by additive manufacturing + interlayer laser heat treatment are further regulated to achieve flexible regulation of the "soft" and "hard" properties of the heterogeneous structure.

[0045] Step 4: Use the additive manufacturing process in step 1 to form high-strength steel. In step 2, the interlayer laser heat treatment process is performed after each two layers of additive manufacturing and on the entire surface area. After additive manufacturing, tempering heat treatment is further performed to prepare Figure 8 High-strength steel with complex heterogeneous structures.

Claims

1. A method for preparing heterogeneous high-strength steel based on interlayer laser heat treatment, characterized in that: The following steps are involved: a. Establish the mapping relationship between the additive manufacturing process parameters of high-strength steel and the size of the quenching and adjacent melt channel self-tempering areas; b. Establish the mapping relationship between the interlayer laser heat treatment process parameters of additively manufactured high-strength steel and the quenching and tempering area dimensions; c. Clarify the variation law of microhardness in quenching and tempering areas of additively manufactured high-strength steel under different post-additive forming heat treatment processes; d. By regulating the interlayer laser heat treatment process parameters and the post-forming heat treatment process parameters, heterogeneous structures of different types and performance matching are designed and prepared to meet the needs of local mechanical properties regulation of high-strength steel in additive manufacturing.

2. The method for preparing heterogeneous high-strength steel based on interlayer laser heat treatment according to claim 1 is characterized in that: The high-strength steel is a high-strength steel material with a martensitic structure as the main component in an additive state, including at least one of tool steel and martensitic stainless steel.

3. The method for preparing heterogeneous high-strength steel based on interlayer laser heat treatment according to claim 1 is characterized in that: The interlayer laser heat treatment adopts an additive manufacturing galvanometer processing system or a separate laser heat treatment galvanometer system, and the laser heat treatment spot adopts a beam shaping method to adopt a rectangular spot with adjustable width.

4. The method for preparing heterogeneous structure high-strength steel based on interlayer laser heat treatment according to claim 1 is characterized in that: The interlayer laser heat treatment adopts infrared fiber laser, the spot width is 0.2-10mm, the laser scanning rate is 5-500mm / s, and the laser power is 300-5000W.

5. The method for preparing heterogeneous structure high-strength steel based on interlayer laser heat treatment according to claim 1, characterized in that: The interlayer laser heat treatment is carried out every other layer or layers in the laser powder bed fusion additive manufacturing process, and the interlayer heat treatment area is the entire additive manufacturing surface or a local area of ​​the additive manufacturing surface.

6. The method for preparing heterogeneous high-strength steel based on interlayer laser heat treatment according to claim 1, characterized in that: The post-additive forming heat treatment process is stress relief annealing or tempering.

7. The method for preparing heterogeneous structure high-strength steel based on interlayer laser heat treatment according to claim 1, characterized in that: The interlayer laser heat treatment process parameters are regulated to include at least one of laser energy density, duty cycle, scanning line spacing, spot size, and spot shape during the laser heat treatment process.

8. The method for preparing heterogeneous high-strength steel based on interlayer laser heat treatment according to claim 1, characterized in that: The heterogeneous structure includes any one of point-shaped, strip-shaped, and layered heterogeneous structures with matching "soft" and "hard" properties in three-dimensional space.

9. The method for preparing heterogeneous structure high-strength steel based on interlayer laser heat treatment according to claim 1, characterized in that: The mechanical properties control mainly includes two types of mechanical properties indicators: strength, hardness, wear resistance, and elongation and impact toughness.

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