A method for improving the strength and toughness of laser additive manufactured maraging steel

Abstract

The application provides a method for improving the strength and toughness of laser additive manufacturing martensitic age hardening steel, and relates to the technical field of preparation of martensitic age hardening steel. The method comprises sequentially performing powder preparation of laser additive manufacturing, heat treatment of powder of laser additive manufacturing, selection of printing process parameters, adjustment of printing process parameters, heat treatment of a printed sample, adjustment of heat treatment process parameters and printing of a final product. In the method, the heat treatment process parameters are optimized, so that the laser melting printing martensitic stainless steel can obtain a dual-state structure composed of fine equiaxed crystals and columnar crystals, and the size of the equiaxed crystals is less than 1 mu m. In the application, the component content of the laser additive manufacturing powder is selected, and the heat treatment process parameters are optimized, so that the method is simple in process steps, convenient to operate, short in processing period and easy to control. The obtained martensitic + reverted austenitic dual structure can synergistically improve the strength and toughness, the matching relationship between the strength and toughness is good, and the method is beneficial to industrial production.

Description

Technical Field

[0001] This invention relates to the technical field of martensitic aging steel preparation, and more particularly to a method for improving the strength and toughness of laser additive manufacturing martensitic aging steel. Background Technology

[0002] Compared with traditional processes, additive manufacturing technology has significant advantages in forming complex and precision structures and components made of difficult-to-machine materials due to its short manufacturing cycle, near-net-shape forming, excellent mechanical properties, strong structural adaptability, and high degree of design freedom.

[0003] Martensitic aging steel is an advanced high-strength steel. After aging heat treatment at 450-550℃, it forms uniformly distributed intermetallic compounds on a martensitic matrix with high dislocation density and good plasticity and toughness. These compounds pin the movement of high-density dislocations in the martensitic matrix, thus acting as a second-phase strengthening agent. Due to its ultra-high strength, good toughness and ductility, excellent weldability, and heat-treated dimensional stability, martensite is widely used in cutting-edge fields such as aerospace, nuclear energy, and high-performance tooling.

[0004] The complex thermal history of additively manufactured martensitic stainless steel offers the possibility of in-situ precipitation strengthening, and the extremely rapid cooling rate yields a high martensite volume fraction. After printing, a specific heat treatment regime forms intermetallic compounds that are uniformly distributed within the martensitic matrix, resulting in second-phase precipitation strengthening. Therefore, a suitable heat treatment regime is essential for improving the strength and toughness of martensitic aging steel. In view of this, this invention proposes a heat treatment method for strengthening and toughening martensitic aging steel manufactured by laser additive manufacturing.

[0005] For example, Chinese patent CN114032472A discloses a novel cobalt-free martensitic aging steel and its strengthening and toughening process. This process involves adjusting the alloying composition of the cobalt-free martensitic aging steel, optimizing the process parameters of two solid solution treatments, and combining three mutually perpendicular deformation treatments, controlled cold treatment, and rapid aging treatment to refine the grain size and regulate and optimize the microstructure. The resulting material exhibits high tensile strength and yield strength, but low elongation.

[0006] Chinese patent CN117265420A discloses martensitic aging steel and its additive manufacturing method. It adopts laser additive manufacturing and direct aging treatment. Although it can reduce the preparation cost of martensitic aging steel in additive manufacturing while maintaining the strength of martensitic aging steel through element ratio, the elongation is low, not exceeding 13%, the strength and plasticity are poor, the laser process parameters are relatively high, and the energy consumption is large.

[0007] Chinese patent CN116732444A discloses an additive manufacturing method for martensitic aging steel. This method significantly reduces the raw material cost of alloy powder and the preparation cost of the alloy while ensuring that the alloy has a high Ms value by adding and adjusting the proportion of high-cost alloying elements. At the same time, combined with the control of additive manufacturing process parameters, fine equiaxed grains and high-density nano-precipitates formed after aging are formed. Although the tensile strength and yield strength of the steel plate after aging treatment are increased, the elongation is further reduced, and the strength and plasticity are not well matched.

[0008] Chinese patent CN116288027A discloses a laser additive manufacturing method for low-density martensitic aging steel and its preparation method. This method overcomes the difficulties in processing and manufacturing high-Al low-density steel by utilizing the advantages of in-situ metallurgy and near-net-shape forming in laser additive manufacturing. Obviously, the prepared material has a low density, and the intermetallic compound precipitates include the B2 phase and L21 phase of Ni-Al-Ti. It also has a low elongation and poor strength and plasticity.

[0009] Chinese patent CN117625903A discloses a method for reducing the yield strength ratio of ultra-high strength martensitic aging steel. However, it targets the heat treatment of the forged structure of martensitic aging steel, and the resulting microstructure is a microstructure with two orientations of martensite laths + fine dispersed precipitates + inverted austenite. Although the tensile strength and yield strength are high, the elongation is low and the strength-plasticity matching effect is poor. Summary of the Invention

[0010] The technical problem to be solved by this invention is that although the strength of maraging steel can be improved by heat treatment in the current preparation of maraging steel, the plasticity is not effectively improved. In order to achieve the improvement of strength and plasticity, alloy composition selection and laser additive manufacturing are adopted. However, alloy composition selection has the technical drawback of high cost, and laser additive manufacturing has the technical drawback of the elongation rate not exceeding 13% while the strength is greatly improved. Therefore, the strength and plasticity cannot be well matched.

[0011] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0012] A method for improving the strength and toughness of laser additive manufacturing maraging steel, comprising the following steps:

[0013] S1. Powder preparation for laser additive manufacturing

[0014] Powders for laser additive manufacturing are prepared by plasma rotary motor atomization.

[0015] S2, Powder heat treatment in laser additive manufacturing

[0016] The powder from S1 laser additive manufacturing is heat-treated to obtain printing powder;

[0017] S3. Printing process parameter selection

[0018] Based on the orthogonal experimental design, multiple laser melting printing process parameters are selected for the optimal region of printing powder using S2.

[0019] S4. Adjustment of printing process parameters

[0020] Various laser melting printing process parameters in S3 were used to actually print various steel samples. The various steel samples were analyzed, and the laser melting printing process parameters corresponding to the steel sample with the best performance index were selected as the adjusted printing process parameters.

[0021] S5. Heat treatment of printed sample

[0022] Multiple printed samples were obtained by laser additive manufacturing according to the adjusted printing process parameters of S4. The multiple printed samples were heat-treated simultaneously, and then air-cooled to room temperature after being removed from the furnace to obtain multiple processed printed samples.

[0023] S6. Adjustment of heat treatment process parameters

[0024] After processing multiple printed samples of S5 into standard tensile specimens, room temperature tensile tests were conducted, and the heat treatment regime with the best mechanical properties was selected as the adjusted heat treatment process parameters.

[0025] S7. Print the final product.

[0026] According to the heat treatment process parameters adjusted in S6, multiple printed samples from S5 were subjected to final heat treatment, and then air-cooled to room temperature after being removed from the furnace to obtain the final product.

[0027] Optionally, the powder composition of laser additive manufacturing in S1 is, by mass percentage, Cr 10-13%, Ni 8-10%, Co 4-6%, Mo 1.5-3%, Si 0.1-0.2%, with the remainder being Fe and unavoidable impurities.

[0028] Optionally, the powder produced by laser additive manufacturing in S1 is a near-spherical powder with a particle size that conforms to that of selective laser melting, and the particle size requirement for near-spherical powder produced by selective laser melting is 25-53 μm.

[0029] Optionally, in S2, the heating rate of the powder heat treatment is 5℃ / min, the holding temperature is 80-90℃, and the holding time is 360-480min.

[0030] Optionally, the optimal region in S3 involves the selection of process parameter ranges for laser power, scanning speed, scanning layer thickness, and scanning spacing.

[0031] Optionally, the steel specimens with the best performance in S4 include those with high density, good surface quality and regular molten pool arrangement selected from the surface morphology and mixed microstructure of the steel specimens analyzed.

[0032] Optionally, the heat treatment in S5 is aging heat treatment, with an aging temperature of 450-550℃ and an aging time of 1-11h.

[0033] Optionally, in S6, a standard tensile specimen is used according to GB / T228-2010; the standard tensile specimen is dog-bone shaped, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm; the room temperature tensile test is performed using a GNT300 electronic universal testing machine equipped with an extensometer, and the tensile rate is 2.5 × 10⁻⁶. -4 mm / s, YS and UTS data can be directly output from the tensile testing device.

[0034] Optionally, the final product in S7 has a dual-phase structure of martensite + restored austenite; wherein the volume fraction of martensite is 50-75%, the shape is lath martensite, and the size is 150-250 nm; the volume fraction of restored austenite is 25-50%, the shape is cell wall-like and located in the interstices of martensite laths, and the size is 100-150 nm.

[0035] Optionally, the density of the final product in S7 is 8.0 ± 0.5 g / cm³. 3 The yield strength is 720-1128 MPa, the tensile strength is 1150-1300 MPa, the yield-to-tensile ratio is 0.60-0.87, the elongation is 14.5-20.3%, and the hardness is 383-440 HV. 1.0 .

[0036] The above technical solution has at least the following advantages compared with the existing technology:

[0037] The above-described solution provides a method for improving the strength and toughness of martensitic aging steel manufactured by laser additive manufacturing. It overcomes the technical defect that the strength and plasticity of current martensitic aging steel cannot be well matched, and can systematically improve the strength and plasticity. The processability and practicality are further expanded, which is conducive to large-scale industrial production and promotion.

[0038] This invention improves the density, performance uniformity, and dimensional accuracy of products by selecting the composition and heat treatment of powders produced through laser additive manufacturing, thereby enhancing the morphology and particle size of the powders during the subsequent laser melting process.

[0039] The method of this invention optimizes the heat treatment process parameters so that the martensitic stainless steel produced by selective laser melting printing can obtain a dual-phase structure composed of fine equiaxed crystals and columnar crystals, with the equiaxed crystal size being less than 1 μm; it can obtain a dual-phase structure of martensite + restored austenite, thereby improving the strength of martensitic aging steel without sacrificing plasticity.

[0040] In this invention, the temperature in the heat treatment process parameters is lower than the phase transformation point of the martensitic aging steel. The heat treatment regime is flexible and can achieve the precipitation of intermetallic compounds without changing the columnar crystal morphology of martensite, thereby synergistically improving the strength and plasticity of the martensitic aging steel.

[0041] This invention can regulate the strength-plasticity matching of martensitic aging steel by adjusting the size and volume fraction of intermetallic compounds through adjusting the heat treatment temperature and time, thereby achieving personalized customization of the mechanical properties of different martensitic aging steels and having a wide range of applications.

[0042] The density of the final product of this invention is 8.0 ± 0.5 g / cm³. 3 The yield strength is 720-1128 MPa, the tensile strength is 1150-1300 MPa, the yield-to-tensile ratio is 0.60-0.87, the elongation is 14.5-20.3%, and the hardness is 383-440 HV. 1.0 .

[0043] In summary, compared with other traditional methods, the method of the present invention has simple process steps, convenient operation, short processing cycle and easy control by selecting the composition content of laser additive manufacturing powder and optimizing the heat treatment process parameters. The obtained martensite + restored austenite bidirectional structure can synergistically improve strength and plasticity, and the strength and plasticity matching relationship is good, which is conducive to industrial production. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a morphology diagram of martensitic aging steel powder used in a method for improving the strength and toughness of martensitic aging steel produced by laser additive manufacturing, as described in Embodiment 1 of the present invention.

[0046] Figure 2 The image shows the dimensions and morphology of a single-pass, single-layer sample in a method for improving the strength and toughness of martensitic aged steel using laser additive manufacturing, as described in Embodiment 1 of the present invention.

[0047] Figure 3This is a microstructure image of the selected area laser melting deposition state in a method for improving the strength and toughness of martensitic aged steel using laser additive manufacturing, as described in Embodiment 1 of the present invention.

[0048] Figure 4 This is a microstructure image of the heat-treated martensitic aging steel in a method for improving the strength and toughness of laser additive manufacturing of martensitic aging steel according to Embodiment 1 of the present invention.

[0049] Figure 5 This refers to the room temperature tensile properties of the martensitic aging steel described in a method for improving the strength and toughness of laser additive manufacturing of martensitic aging steel according to Embodiment 1 of the present invention.

[0050] Figure 6 This is a schematic diagram of the process flow for a method to improve the strength and toughness of martensitic aging steel produced by laser additive manufacturing, according to Embodiment 1 of the present invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0052] A method for improving the strength and toughness of laser additive manufacturing maraging steel, comprising the following steps:

[0053] S1. Powder preparation for laser additive manufacturing

[0054] Powders for laser additive manufacturing are prepared by plasma rotary motor atomization.

[0055] S2, Powder heat treatment in laser additive manufacturing

[0056] The powder from S1 laser additive manufacturing is heat-treated to obtain printing powder;

[0057] S3. Printing process parameter selection

[0058] Based on the orthogonal experimental design, multiple laser melting printing process parameters are selected for the optimal region of printing powder using S2.

[0059] S4. Adjustment of printing process parameters

[0060] Various laser melting printing process parameters in S3 were used to actually print various steel samples. The various steel samples were analyzed, and the laser melting printing process parameters corresponding to the steel sample with the best performance index were selected as the adjusted printing process parameters.

[0061] S5. Heat treatment of printed sample

[0062] Multiple printed samples were obtained by laser additive manufacturing according to the adjusted printing process parameters of S4. The multiple printed samples were heat-treated simultaneously, and then air-cooled to room temperature after being removed from the furnace to obtain multiple processed printed samples.

[0063] S6. Adjustment of heat treatment process parameters

[0064] After processing multiple printed samples of S5 into standard tensile specimens, room temperature tensile tests were conducted, and the heat treatment regime with the best mechanical properties was selected as the adjusted heat treatment process parameters.

[0065] S7. Print the final product.

[0066] According to the heat treatment process parameters adjusted in S6, multiple printed samples from S5 were subjected to final heat treatment, and then air-cooled to room temperature after being removed from the furnace to obtain the final product.

[0067] Specifically, the powder composition of laser additive manufacturing in S1 is as follows by mass percentage: Cr 10-13%, Ni 8-10%, Co 4-6%, Mo 1.5-3%, Si 0.1-0.2%, with the remainder being Fe and unavoidable impurities.

[0068] Specifically, the powder produced by laser additive manufacturing in S1 is a near-spherical powder with a particle size that conforms to that of selective laser melting, and the particle size requirement for near-spherical powder produced by selective laser melting is 25-53 μm.

[0069] Specifically, in S2, the heating rate of the powder heat treatment is 5℃ / min, the holding temperature is 80-90℃, and the holding time is 360-480min.

[0070] Specifically, the optimal selection area in S3 involves the selection of process parameter ranges for laser power, scanning speed, scanning layer thickness, and scanning spacing.

[0071] Specifically, the steel specimens with the best performance in S4 include those with mixed surface morphology and microstructure, selected from which steel specimens with high density, good surface quality and regular molten pool arrangement are selected.

[0072] Specifically, the heat treatment in S5 is aging heat treatment, with an aging temperature of 450-550℃ and an aging time of 1-11 hours.

[0073] Specifically, in S6, a standard tensile specimen is used according to GB / T228-2010; the standard tensile specimen is dog-bone shaped, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm; the room temperature tensile test is performed using a GNT300 electronic universal testing machine equipped with an extensometer, and the tensile rate is 2.5 × 10⁻⁶. -4 mm / s, YS and UTS data can be directly output from the tensile testing device.

[0074] Specifically, the final product in S7 has a dual-phase structure of martensite and restored austenite; the volume fraction of martensite is 50-75%, the shape is lath martensite, and the size is 150-250 nm; the volume fraction of restored austenite is 25-50%, the shape is cell wall-like and located in the interstices of martensite laths, and the size is 100-150 nm.

[0075] Specifically, the density of the final product in S7 is 8.0 ± 0.5 g / cm³. 3 The yield strength is 720-1128 MPa, the tensile strength is 1150-1300 MPa, the yield-to-tensile ratio is 0.60-0.87, the elongation is 14.5-20.3%, and the hardness is 383-440 HV. 1.0 .

[0076] Example 1

[0077] A method for improving the strength and toughness of laser additive manufacturing maraging steel, wherein the method for improving the strength and toughness of laser additive manufacturing maraging steel is combined with Figure 6 The following steps are required:

[0078] S1. Powder preparation for laser additive manufacturing

[0079] Powder for laser additive manufacturing was prepared by plasma rotary motor atomization. The powder composition, by mass percentage, was Cr 11.3%, Ni 8.0%, Co 5.37%, Mo 2.6%, Si 0.20%, with the remainder being Fe and unavoidable impurities. Figure 1 As shown, the powder produced by laser additive manufacturing is a near-spherical powder with a particle size conforming to that of selective laser melting, and the average particle size of the near-spherical powder is 33 μm;

[0080] S2, Powder heat treatment in laser additive manufacturing

[0081] The powder produced by S1 laser additive manufacturing was subjected to heat treatment at a heating rate of 5℃ / s, a holding temperature of 80℃, and a holding time of 480min to obtain printing powder.

[0082] S3. Printing process parameter selection

[0083] Based on the orthogonal experimental design method, the optimal region for selecting printing powder using S2 is determined by various laser melting printing process parameters. The optimal region involves the selection of process parameter ranges for laser power, scanning speed, scanning layer thickness, and scanning spacing.

[0084] S4. Adjustment of printing process parameters

[0085] Multiple laser melting printing process parameters from S3 were used to print various steel samples. These samples were analyzed, and the laser melting printing process parameters corresponding to the steel sample with the optimal performance were selected as the adjusted printing process parameters. The steel sample with the optimal performance included those with high density, good surface quality, and regular melt pool arrangement, selected from the analyzed surface morphology and mixed microstructure. The dimensions and morphology of a single-pass, single-layer sample are shown in the image below. Figure 2 As shown, the microstructure morphology of the selected area laser melting deposition state is as follows: Figure 3 As shown;

[0086] S5. Heat treatment of printed sample

[0087] Multiple printed samples were obtained by laser additive manufacturing according to the adjusted printing process parameters of S4. These samples were then simultaneously subjected to aging heat treatment at 450℃ for 3 hours. After aging, the samples were air-cooled to room temperature, resulting in multiple processed printed samples. The microstructure of the heat-treated martensitic aged steel is shown in the image below. Figure 4 As shown;

[0088] S6. Adjustment of heat treatment process parameters

[0089] Multiple printed samples from S5 were processed into standard tensile specimens and then subjected to room temperature tensile tests. The standard tensile specimens were dog-bone shaped, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm. Room temperature tensile tests were conducted using a GNT300 electronic universal testing machine equipped with an extensometer, at a tensile rate of 2.5 × 10⁻⁶. -4 mm / s; the optimal heat treatment regime for mechanical properties was selected as the adjusted heat treatment process parameters; room temperature tensile properties data of martensitic aging steel are as follows: Figure 5 As shown;

[0090] S7. Print the final product.

[0091] According to the heat treatment process parameters adjusted in S6, multiple printed samples from S5 were subjected to final heat treatment, and then air-cooled to room temperature after being removed from the furnace to obtain the final product.

[0092] The final product prepared in this embodiment has a microstructure of martensite + restored austenite in a dual-phase structure; wherein, the volume fraction of martensite is 70%, the shape is lath martensite with a size of 150 nm, the volume fraction of restored austenite is 30%, the shape is cell wall-like, located in the interstices of martensite laths, and the size is generally 120 nm.

[0093] The density of the final product prepared in this embodiment is 8.0 ± 0.1 g / cm³. 3 The yield strength is 914.3 MPa, the tensile strength is 1160.4 MPa, the yield-to-tensile ratio is 0.78, the elongation is 20.05%, and the hardness is 386 HV. 1.0 .

[0094] Example 2

[0095] A method for improving the strength and toughness of laser additive manufacturing maraging steel, comprising the following steps:

[0096] S1. Powder preparation for laser additive manufacturing

[0097] Powder for laser additive manufacturing was prepared by plasma rotary motor atomization. The composition of the laser additive manufacturing powder, by mass percentage, was Cr 10.8%, Ni 8.0%, Co 4.0%, Mo 1.5%, Si 0.15%, with the remainder being Fe and unavoidable impurities. The laser additive manufacturing powder was a near-spherical powder with a particle size conforming to selective laser melting, and the average particle size of the near-spherical powder was 31 μm.

[0098] S2, Powder heat treatment in laser additive manufacturing

[0099] The powder produced by S1 laser additive manufacturing was subjected to heat treatment at a heating rate of 5℃ / s, a holding temperature of 80℃, and a holding time of 480min to obtain printing powder.

[0100] S3. Printing process parameter selection

[0101] Based on the orthogonal experimental design method, the optimal region for selecting printing powder using S2 is determined by various laser melting printing process parameters. The optimal region involves the selection of process parameter ranges for laser power, scanning speed, scanning layer thickness, and scanning spacing.

[0102] S4. Adjustment of printing process parameters

[0103] Various laser melting printing process parameters in S3 were used to actually print various steel samples. The various steel samples were analyzed, and the laser melting printing process parameters corresponding to the steel sample with the best performance index were selected as the adjusted printing process parameters. Among them, the steel sample with the best performance index includes the steel sample with high density, good surface quality and regular molten pool arrangement, which was selected from the surface morphology and mixed microstructure of the steel sample.

[0104] S5. Heat treatment of printed sample

[0105] Multiple printed samples were obtained by laser additive manufacturing according to the adjusted printing process parameters of S4. The multiple printed samples were then subjected to heat treatment at the same time. The heat treatment was aging heat treatment at a temperature of 500℃ for 3 hours. After being removed from the furnace, they were air-cooled to room temperature to obtain multiple printed samples after treatment.

[0106] S6. Adjustment of heat treatment process parameters

[0107] Multiple printed samples from S5 were processed into standard tensile specimens and then subjected to room temperature tensile tests. The standard tensile specimens were dog-bone shaped, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm. Room temperature tensile tests were conducted using a GNT300 electronic universal testing machine equipped with an extensometer, at a tensile rate of 2.5 × 10⁻⁶. -4 mm / s; Select the heat treatment regime with the optimal mechanical properties as the adjusted heat treatment process parameters.

[0108] S7. Print the final product.

[0109] According to the heat treatment process parameters adjusted in S6, multiple printed samples from S5 were subjected to final heat treatment, and then air-cooled to room temperature after being removed from the furnace to obtain the final product.

[0110] The final product prepared in this embodiment has a microstructure of martensite + restored austenite in a dual-phase structure; wherein, the volume fraction of martensite is 57%, the shape is lath martensite with a size of 150 nm, the volume fraction of restored austenite is 43%, the shape is cell wall-like, located in the interstices of martensite laths, and the size is generally 130 nm.

[0111] The density of the final product prepared in this embodiment is 7.85 ± 0.5 g / cm³. 3 The yield strength is 935.5 MPa, the tensile strength is 1187.4 MPa, the yield-to-tensile ratio is 0.788, the elongation is 16.65%, and the hardness is 395 HV. 1.0 .

[0112] Example 3

[0113] A method for improving the strength and toughness of laser additive manufacturing maraging steel, comprising the following steps:

[0114] S1. Powder preparation for laser additive manufacturing

[0115] Powder for laser additive manufacturing was prepared by plasma rotary motor atomization. The composition of the laser additive manufacturing powder, by mass percentage, was Cr 11.3%, Ni 8.28%, Co 5.3%, Mo 1.5%, Si 0.2%, with the remainder being Fe and unavoidable impurities. The laser additive manufacturing powder was a near-spherical powder with a particle size conforming to selective laser melting, and the average particle size of the near-spherical powder was 25 μm.

[0116] S2, Powder heat treatment in laser additive manufacturing

[0117] The powder produced by S1 laser additive manufacturing was subjected to heat treatment at a heating rate of 5℃ / min, a holding temperature of 80℃, and a holding time of 480min to obtain printing powder.

[0118] S3. Printing process parameter selection

[0119] Based on the orthogonal experimental design method, the optimal region for selecting printing powder using S2 is determined by various laser melting printing process parameters. The optimal region involves the selection of process parameter ranges for laser power, scanning speed, scanning layer thickness, and scanning spacing.

[0120] S4. Adjustment of printing process parameters

[0121] Various laser melting printing process parameters in S3 were used to actually print various steel samples. The various steel samples were analyzed, and the laser melting printing process parameters corresponding to the steel sample with the best performance index were selected as the adjusted printing process parameters. Among them, the steel sample with the best performance index includes the steel sample with high density, good surface quality and regular molten pool arrangement, which was selected from the surface morphology and mixed microstructure of the steel sample.

[0122] S5. Heat treatment of printed sample

[0123] Multiple printed samples were obtained by laser additive manufacturing according to the adjusted printing process parameters of S4. The multiple printed samples were then subjected to heat treatment at the same time. The heat treatment was aging heat treatment at a temperature of 500℃ for 5 hours. After being removed from the furnace, they were air-cooled to room temperature to obtain multiple printed samples after treatment.

[0124] S6. Adjustment of heat treatment process parameters

[0125] Multiple printed samples from S5 were processed into standard tensile specimens and then subjected to room temperature tensile tests. The standard tensile specimens were dog-bone shaped, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm. Room temperature tensile tests were conducted using a GNT300 electronic universal testing machine equipped with an extensometer, at a tensile rate of 2.5 × 10⁻⁶. -4 mm / s; Select the heat treatment regime with the optimal mechanical properties as the adjusted heat treatment process parameters.

[0126] S7. Print the final product.

[0127] According to the heat treatment process parameters adjusted in S6, multiple printed samples from S5 were subjected to final heat treatment, and then air-cooled to room temperature after being removed from the furnace to obtain the final product.

[0128] The final product prepared in this embodiment has a microstructure of martensite + restored austenite in a dual-phase structure; wherein, the volume fraction of martensite is 53.4%, the shape is lath martensite with a size of 160 nm, the volume fraction of restored austenite is 46%, the shape is cell wall-like, located in the interstices of martensite laths, and the size is generally 140 nm.

[0129] The density of the final product prepared in this embodiment is 7.80 ± 0.2 g / cm³. 3 The yield strength is 949.72 MPa, the tensile strength is 1239.1 MPa, the yield-to-tensile ratio is 0.76, the elongation is 14.6%, and the hardness is 410.3 HV. 1.0 .

[0130] Example 4

[0131] A method for improving the strength and toughness of laser additive manufacturing maraging steel, comprising the following steps:

[0132] S1. Powder preparation for laser additive manufacturing

[0133] Powder for laser additive manufacturing was prepared by plasma rotary motor atomization. The composition of the laser additive manufacturing powder, by mass percentage, was Cr 11.1%, Ni 8.53%, Co 5.0%, Mo 2.60%, Si 0.10%, with the remainder being Fe and unavoidable impurities. The laser additive manufacturing powder was a near-spherical powder with a particle size conforming to selective laser melting, and the average particle size of the near-spherical powder was 40 μm.

[0134] S2, Powder heat treatment in laser additive manufacturing

[0135] The powder produced by S1 laser additive manufacturing was subjected to heat treatment at a heating rate of 5℃ / min, a holding temperature of 80℃, and a holding time of 480min to obtain printing powder.

[0136] S3. Printing process parameter selection

[0137] Based on the orthogonal experimental design method, the optimal region for selecting printing powder using S2 is determined by various laser melting printing process parameters. The optimal region involves the selection of process parameter ranges for laser power, scanning speed, scanning layer thickness, and scanning spacing.

[0138] S4. Adjustment of printing process parameters

[0139] Various laser melting printing process parameters in S3 were used to actually print various steel samples. The various steel samples were analyzed, and the laser melting printing process parameters corresponding to the steel sample with the best performance index were selected as the adjusted printing process parameters. Among them, the steel sample with the best performance index includes the steel sample with high density, good surface quality and regular molten pool arrangement, which was selected from the surface morphology and mixed microstructure of the steel sample.

[0140] S5. Heat treatment of printed sample

[0141] Multiple printed samples were obtained by laser additive manufacturing according to the adjusted printing process parameters of S4. The multiple printed samples were then subjected to heat treatment at the same time. The heat treatment was aging heat treatment at a temperature of 450℃ for 7 hours. After being removed from the furnace, they were air-cooled to room temperature to obtain multiple printed samples after treatment.

[0142] S6. Adjustment of heat treatment process parameters

[0143] Multiple printed samples from S5 were processed into standard tensile specimens and then subjected to room temperature tensile tests. The standard tensile specimens were dog-bone shaped, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm. Room temperature tensile tests were conducted using a GNT300 electronic universal testing machine equipped with an extensometer, at a tensile rate of 2.5 × 10⁻⁶. -4 mm / s; Select the heat treatment regime with the optimal mechanical properties as the adjusted heat treatment process parameters.

[0144] S7. Print the final product.

[0145] According to the heat treatment process parameters adjusted in S6, multiple printed samples from S5 were subjected to final heat treatment, and then air-cooled to room temperature after being removed from the furnace to obtain the final product.

[0146] The final product prepared in this embodiment has a microstructure of martensite + restored austenite in a dual-phase structure; wherein, the volume fraction of martensite is 60%, the shape is lath martensite with a size of 160 nm, the volume fraction of restored austenite is 40%, the shape is cell wall-like, located in the interstices of martensite laths, and the size is generally 130 nm.

[0147] The density of the final product prepared in this embodiment is 8.0 ± 0.15 g / cm³. 3 The yield strength is 731.78 MPa, the tensile strength is 1214.1 MPa, the yield-to-tensile ratio is 0.60, the elongation is 18.0%, and the hardness is 404 HV. 1.0 .

[0148] Example 5

[0149] A method for improving the strength and toughness of laser additive manufacturing maraging steel, comprising the following steps:

[0150] S1. Powder preparation for laser additive manufacturing

[0151] Powder for laser additive manufacturing was prepared by plasma rotary motor atomization. The composition of the laser additive manufacturing powder, by mass percentage, was Cr 10.0%, Ni 9.20%, Co 4.47%, Mo 1.80%, Si 0.15%, with the remainder being Fe and unavoidable impurities. The laser additive manufacturing powder was a near-spherical powder with a particle size conforming to selective laser melting, and the average particle size of the near-spherical powder was 35 μm.

[0152] S2, Powder heat treatment in laser additive manufacturing

[0153] The powder produced by S1 laser additive manufacturing was subjected to heat treatment at a heating rate of 5℃ / min, a holding temperature of 80℃, and a holding time of 480min to obtain printing powder.

[0154] S3. Printing process parameter selection

[0155] Based on the orthogonal experimental design method, the optimal region for selecting printing powder using S2 is determined by various laser melting printing process parameters. The optimal region involves the selection of process parameter ranges for laser power, scanning speed, scanning layer thickness, and scanning spacing.

[0156] S4. Adjustment of printing process parameters

[0157] Various laser melting printing process parameters in S3 were used to actually print various steel samples. The various steel samples were analyzed, and the laser melting printing process parameters corresponding to the steel sample with the best performance index were selected as the adjusted printing process parameters. Among them, the steel sample with the best performance index includes the steel sample with high density, good surface quality and regular molten pool arrangement, which was selected from the surface morphology and mixed microstructure of the steel sample.

[0158] S5. Heat treatment of printed sample

[0159] Multiple printed samples were obtained by laser additive manufacturing according to the adjusted printing process parameters of S4. The multiple printed samples were then subjected to heat treatment at the same time. The heat treatment was aging heat treatment at a temperature of 500℃ for 7 hours. After being removed from the furnace, they were air-cooled to room temperature to obtain multiple printed samples after treatment.

[0160] S6. Adjustment of heat treatment process parameters

[0161] Multiple printed samples from S5 were processed into standard tensile specimens and then subjected to room temperature tensile tests. The standard tensile specimens were dog-bone shaped, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm. Room temperature tensile tests were conducted using a GNT300 electronic universal testing machine equipped with an extensometer, at a tensile rate of 2.5 × 10⁻⁶. -4 mm / s; Select the heat treatment regime with the optimal mechanical properties as the adjusted heat treatment process parameters.

[0162] S7. Print the final product.

[0163] According to the heat treatment process parameters adjusted in S6, multiple printed samples from S5 were subjected to final heat treatment, and then air-cooled to room temperature after being removed from the furnace to obtain the final product.

[0164] The final product prepared in this embodiment has a microstructure of martensite + restored austenite in a dual-phase structure; wherein, the volume fraction of martensite is 63.4%, the shape is lath martensite with a size of 150 nm, the volume fraction of restored austenite is 36.6%, the shape is cell wall-like, located in the interstices of martensite laths, and the size is generally 130 nm.

[0165] The density of the final product prepared in this embodiment is 8.0 ± 0.05 g / cm³. 3 The yield strength is 976.16 MPa, the tensile strength is 1276.84 MPa, the yield-to-tensile ratio is 0.76, the elongation is 14.8%, and the hardness is 425.7 HV. 1.0 .

[0166] Example 6

[0167] A method for improving the strength and toughness of laser additive manufacturing maraging steel, comprising the following steps:

[0168] S1. Powder preparation for laser additive manufacturing

[0169] Powder for laser additive manufacturing was prepared by plasma rotary motor atomization. The composition of the laser additive manufacturing powder, by mass percentage, was Cr 11.0%, Ni 8.48%, Co 5.40%, Mo 2.0%, Si 0.19%, with the remainder being Fe and unavoidable impurities. The laser additive manufacturing powder was a near-spherical powder with a particle size conforming to selective laser melting, and the average particle size of the near-spherical powder was 44 μm.

[0170] S2, Powder heat treatment in laser additive manufacturing

[0171] The powder produced by S1 laser additive manufacturing was subjected to heat treatment at a heating rate of 5℃ / min, a holding temperature of 80℃, and a holding time of 480min to obtain printing powder.

[0172] S3. Printing process parameter selection

[0173] Based on the orthogonal experimental design method, the optimal region for selecting printing powder using S2 is determined by various laser melting printing process parameters. The optimal region involves the selection of process parameter ranges for laser power, scanning speed, scanning layer thickness, and scanning spacing.

[0174] S4. Adjustment of printing process parameters

[0175] Various laser melting printing process parameters in S3 were used to actually print various steel samples. The various steel samples were analyzed, and the laser melting printing process parameters corresponding to the steel sample with the best performance index were selected as the adjusted printing process parameters. Among them, the steel sample with the best performance index includes the steel sample with high density, good surface quality and regular molten pool arrangement, which was selected from the surface morphology and mixed microstructure of the steel sample.

[0176] S5. Heat treatment of printed sample

[0177] Multiple printed samples were obtained by laser additive manufacturing according to the adjusted printing process parameters of S4. The multiple printed samples were then subjected to heat treatment at the same time. The heat treatment was aging heat treatment at a temperature of 550℃ for 9 hours. After being removed from the furnace, they were air-cooled to room temperature to obtain multiple printed samples after treatment.

[0178] S6. Adjustment of heat treatment process parameters

[0179] Multiple printed samples from S5 were processed into standard tensile specimens and then subjected to room temperature tensile tests. The standard tensile specimens were dog-bone shaped, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm. Room temperature tensile tests were conducted using a GNT300 electronic universal testing machine equipped with an extensometer, at a tensile rate of 2.5 × 10⁻⁶. -4 mm / s; Select the heat treatment regime with the optimal mechanical properties as the adjusted heat treatment process parameters.

[0180] S7. Print the final product.

[0181] According to the heat treatment process parameters adjusted in S6, multiple printed samples from S5 were subjected to final heat treatment, and then air-cooled to room temperature after being removed from the furnace to obtain the final product.

[0182] The final product prepared in this embodiment has a microstructure of martensite + restored austenite in a dual-phase structure; wherein, the volume fraction of martensite is 70%, the shape is lath martensite with a size of 165nm, the volume fraction of restored austenite is 30%, the shape is cell wall-like, located in the interstices of martensite laths, and the size is generally 130nm.

[0183] The density of the final product prepared in this embodiment is 8.05 ± 0.05 g / cm³. 3 The yield strength is 1125.6 MPa, the tensile strength is 1305.9 MPa, the yield-to-tensile ratio is 0.862, the elongation is 17.8%, and the hardness is 435 HV. 1.0 .

[0184] The above-described solution provides a method for improving the strength and toughness of martensitic aging steel manufactured by laser additive manufacturing. It overcomes the technical defect that the strength and plasticity of current martensitic aging steel cannot be well matched, and can systematically improve the strength and plasticity. The processability and practicality are further expanded, which is conducive to large-scale industrial production and promotion.

[0185] This invention improves the density, performance uniformity, and dimensional accuracy of products by selecting the composition and heat treatment of powders produced through laser additive manufacturing, thereby enhancing the morphology and particle size of the powders during the subsequent laser melting process.

[0186] The method of this invention optimizes the heat treatment process parameters so that the martensitic stainless steel produced by selective laser melting printing can obtain a dual-phase structure composed of fine equiaxed crystals and columnar crystals, with the equiaxed crystal size being less than 1 μm; it can obtain a dual-phase structure of martensite + restored austenite, thereby improving the strength of martensitic aging steel without sacrificing plasticity.

[0187] In this invention, the temperature in the heat treatment process parameters is lower than the phase transformation point of the martensitic aging steel. The heat treatment regime is flexible and can achieve the precipitation of intermetallic compounds without changing the columnar crystal morphology of martensite, thereby synergistically improving the strength and plasticity of the martensitic aging steel.

[0188] This invention can regulate the strength-plasticity matching of martensitic aging steel by adjusting the size and volume fraction of intermetallic compounds through adjusting the heat treatment temperature and time, thereby achieving personalized customization of the mechanical properties of different martensitic aging steels and having a wide range of applications.

[0189] The density of the final product of this invention is 8.0 ± 0.5 g / cm³. 3 The yield strength is 720-1128 MPa, the tensile strength is 1150-1300 MPa, the yield-to-tensile ratio is 0.60-0.87, the elongation is 14.5-20.3%, and the hardness is 383-440 HV. 1.0 .

[0190] In summary, compared with other traditional methods, the method of the present invention has simple process steps, convenient operation, short processing cycle and easy control by selecting the composition content of laser additive manufacturing powder and optimizing the heat treatment process parameters. The obtained martensite + restored austenite bidirectional structure can synergistically improve strength and plasticity, and the strength and plasticity matching relationship is good, which is conducive to industrial production.

[0191] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of improving the strengthening and toughening of a laser additive manufactured maraging steel, characterized in that, The method for improving the strength and toughness of laser additive manufacturing maraging steel comprises the following steps: S1, laser additive manufacturing powder preparation The laser additive manufacturing powder is prepared by plasma rotating electrode atomization, and the composition of the laser additive manufacturing powder comprises, by mass percentage, Cr 10-13%, Ni 8-10%, Co 4-6%, Mo 1.5-3%, Si 0.1-0.2%, and the balance of Fe and inevitable impurities; S2, heat treatment of the laser additive manufacturing powder The laser additive manufacturing powder prepared in S1 is subjected to heat treatment, the heating rate of the heat treatment of the powder is 5 ℃ / min, the holding temperature is 80-90 ℃, and the holding time is 360-480 min, so as to obtain a printing powder; S3, selection of printing process parameters According to the orthogonal experiment method, the optimal selection zone laser melting printing process parameters are selected based on the printing powder of S2; S4, adjustment of the printing process parameters The laser melting printing process parameters in S3 are used for actual printing to obtain a plurality of steel samples, the plurality of steel samples are analyzed, the laser melting printing process parameters corresponding to the steel sample with the optimal performance index are selected as the adjusted printing process parameters; S5, heat treatment of the printing sample The laser additive manufacturing is performed according to the adjusted printing process parameters of S4 to obtain a plurality of printing sample parts, the plurality of printing sample parts are simultaneously subjected to heat treatment, the heat treatment is aging heat treatment, the aging treatment temperature is 450-550 ℃, and the aging treatment time is 1-11 h; the furnace is discharged and air-cooled to room temperature to obtain a plurality of treated printing sample parts; S6, adjustment of the heat treatment process parameters After the plurality of printing sample parts of S5 are processed into standard tensile samples, the room temperature tensile test is performed, and the heat treatment system with the optimal mechanical property is selected as the adjusted heat treatment process parameter; S7, final printing product The final heat treatment is performed on the plurality of printing sample parts of S5 according to the adjusted heat treatment process parameters of S6, the furnace is discharged and air-cooled to room temperature to obtain a final product; the microstructure of the final product is a dual-phase structure of martensite + reverted austenite; the volume fraction of the martensite is 50-75%, the shape of the martensite is lath martensite, and the size of the martensite is 150-250 nm; the volume fraction of the reverted austenite is 25-50%, the shape of the reverted austenite is cell wall-shaped and located in the gap between the martensite laths, and the size of the reverted austenite is 100-150 nm.

2. The method of improving the strength and toughness of a laser additive manufactured maraging steel of claim 1, wherein, The laser additive manufacturing powder in S1 is a near-spherical powder with a particle size meeting the requirements of selective laser melting, and the particle size of the near-spherical powder for selective laser melting is required to be 25-53 μm.

3. The method of improving the strength and toughness of a laser additive manufactured maraging steel of claim 1, wherein, In S3, the optimal selection zone involves the selection of the process parameter ranges of laser power, scanning speed, scanning layer thickness, and scanning spacing.

4. The method of improving the strength and toughness of a laser additive manufactured maraging steel of claim 1, wherein, In S4, the steel sample with the optimal performance index includes analysis of the surface morphology and mixed microstructure of the steel sample, and the steel sample with high density, good surface quality, and regular molten pool arrangement is selected.

5. The method of increasing the strength and toughness of a laser additive manufactured maraging steel of claim 1, wherein, S6 In accordance with GB / T 228-2010, standard tensile samples were used; the shape of the standard tensile sample was dog bone, with a gauge length of 15 mm, a diameter of 2.5 mm, and a total length of 40 mm; room temperature tensile tests were performed on an electronic universal testing machine GNT300 equipped with an extensometer, at a tensile rate of 2.5 x 10 -4 mm / s, and YS and UTS data could be directly output by the tensile testing device.

6. The method of improving the strength and toughness of a laser additive manufactured maraging steel of claim 1, wherein, The density of the final product in S7 is 8.0 ± 0.5 g / cm3 3 , the yield strength is 720-1128 MPa, the tensile strength is 1150-1300 MPa, the yield strength ratio is 0.60-0.87, the elongation is 14.5-20.3%, and the hardness is 383-440 HV 1.0 .

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