Additive manufacturing fully-compact stainless steel capable of eliminating anisotropy and preparation method of additive manufacturing fully-compact stainless steel

Abstract

The invention discloses additive manufacturing fully-compact stainless steel capable of eliminating anisotropy and a preparation method thereof, and the preparation method comprises the step of realizing synchronous optimization of a microscopic structure and mechanical properties of a material through a multi-procedure collaborative process of powder mixing, selective laser cladding, gradient heat treatment and pulse hot isostatic pressing treatment. The solidification behavior of a molten pool is innovatively regulated and controlled through high-entropy alloy elements, and the mechanical property is greatly improved by adding nano ceramic particles. Grain preferred orientation is eliminated in combination with gradient heat treatment, internal defects are eliminated in cooperation with pulse hot isostatic pressing, and finally a component with high compactness (larger than or equal to 99.8%) and isotropic mechanical properties is obtained. The strength difference of samples in the vertical and parallel construction directions is less than 1.5%, and the elongation deviation is less than 2%. The method has the characteristics of being high in process controllability, high in finished product consistency and the like, and is suitable for batch production of complex structural parts in the fields of aerospace, medical instruments and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular relates to an additive manufacturing method for eliminating anisotropy and fully dense stainless steel and a preparation method thereof. Background Art

[0002] Stainless steel currently accounts for over 80% of engineering metal components. Its excellent balance of strength and ductility, as well as its corrosion resistance, make it irreplaceable in high-tech fields such as nuclear power equipment, deep-sea vessels, and aerospace. However, with the rapid development of industrial equipment towards lightweight and efficient manufacturing, traditional manufacturing processes have shown significant limitations in achieving complex topologically optimized structures.

[0003] Additive manufacturing technology, through a layer-by-layer stacking process, breaks through the geometric constraints of traditional subtractive manufacturing, providing an innovative solution for the fabrication of complex components with lightweight features such as lattice filling and thin-walled cavities. This technology is particularly suitable for achieving gradient density structures based on topology optimization, which can reduce component weight by 30%-50% while maintaining the same load-bearing capacity. However, in-depth research has shown that whether based on powder bed fusion (PBF), electron beam selective melting (EBM) arc additive manufacturing (WAAM), or directed energy deposition (DED) technology, the formed parts all exhibit significant anisotropy in mechanical properties: yield strength fluctuations along the deposition direction can reach 20%-35%, and elongation differences exceed 50%. This anisotropic grain growth and microstructural inhomogeneity, resulting from the rapid solidification process, lead to unpredictable failure modes in actual service, severely restricting the application of additively manufactured stainless steel in load-bearing components.

[0004] At present, the method for improving anisotropy mainly relies on post-processing technology. Existing patented technologies are mostly concentrated on specific alloys (such as titanium alloys) or traditional cold-rolled plates (such as Ansteel Lianzhong's 439 cold-rolled plate anisotropy optimization patent: CN116024415B), while the technology for regulating the anisotropy of the mechanical properties of additively manufactured stainless steel is still blank. Therefore, the development of special powders that can eliminate the anisotropy of the mechanical properties of stainless steel 3D printing, and the exploration of additive manufacturing methods that effectively regulate the evolution of microstructures and eliminate the anisotropy of mechanical properties have become key technical requirements for breaking through the bottleneck of the industrialization of this technology and realizing the reliable manufacturing of high-performance lightweight components.

[0005] Eliminating anisotropy means eliminating the directionality of the structure. There are two methods: one is to control the growth process and reduce the grain size. The structure of traditional additively manufactured parts shows columnar crystals along the construction direction. Refining the grains can eliminate the directionality of the grain morphology and avoid the appearance of grains across the melt pool. Reducing the grain size can also weaken the preferred orientation; the second is post-processing, which allows the structure to regrow and eliminate the preferred orientation. However, simply refining the grains cannot eliminate the tendency of preferred orientation of grains in additive parts. Post-processing cannot refine the grains, but will make the particles coarser. Only by combining the two can we eliminate microstructural anisotropy while maintaining high mechanical properties synergistically. In this study, elements such as Ti, Al, Ce, TiB2, Mo and Mn were added to AISI 304L stainless steel powder. The introduction of heterogeneous metal powders and nano-ceramic particles played a strong role in refining the grains and significantly improved the mechanical properties of the 304L matrix. Pulsed hot isostatic pressing is used to promote multi-directional plastic deformation through periodic loading and unloading (square wave or sine wave), breaking the columnar crystals and texture unique to additive manufacturing, inducing the formation of equiaxed recrystallized grains, and significantly reducing the directional dependence of mechanical properties. Dynamic pressure fluctuations also apply multi-angle compression forces to pores and unfused defects, reducing the distribution of anisotropic defects. Mo and Mn ensure the structural stability of parts during heat treatment and delay the Mn 23 The precipitation of C6 at the grain boundaries prevents abnormal grain growth or the formation of brittle martensite phase. Summary of the Invention

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0007] The purpose of the present invention is to fill the gap in the prior art and provide an additively manufactured fully dense stainless steel and a preparation method thereof that eliminates anisotropy.

[0008] To solve the above technical problems, the present invention provides the following technical solutions: an additively manufactured fully dense stainless steel with anisotropy eliminated, characterized by comprising AISI 304L powder, Ti, Al, Ce, TiB2, Mo, and Mn;

[0009] Calculated by raw material mass percentage, the AISI 304L powder content is 85.0-95.0%, the Ti content is 1.5-3.5%, the Al content is 1.0-3.0%, the Ce content is 0.1-0.5%, the Ti B2 content is 0.5-5.0%, the Mo content is 1.0-2.0%, and the Mn content is 0.5-1.5%.

[0010] As a preferred solution for additively manufacturing fully dense stainless steel according to the present invention, the AISI 304L powder has, by weight percentage of raw materials, an AISI content of 87.5-92.5%, a Ti content of 2.0-3.0%, an Al content of 1.5-2.5%, a Ce content of 0.2-0.4%, a TiB2 content of 1.5-2.5%, a Mo content of 1.2-1.5%, and a Mn content of 0.6-1.0%.

[0011] As a preferred solution for additive manufacturing of fully dense stainless steel according to the present invention, the AISI 304L powder content, calculated by weight percentage of raw materials, is 90.6%, the Ti content is 2.5%, the Al content is 2.0%, the Ce content is 0.3%, the TiB2 content is 2.1%, the Mo content is 1.5%, and the Mn content is 1.0%.

[0012] Another object of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing additively manufactured fully dense stainless steel that eliminates anisotropy, characterized in that the raw materials are additively manufactured, and then gradient heat treatment and pulse hot isostatic pressing are performed to obtain the additively manufactured fully dense stainless steel.

[0013] As a preferred embodiment of the preparation method of the present invention, the raw materials are mixed in a planetary ball mill before additive manufacturing, and zirconium oxide balls are added and fully mixed, with a ball-to-material ratio of 1:1, a ball milling speed of 50 to 300 rpm, and a ball milling time of 2 to 10 hours.

[0014] As a preferred embodiment of the preparation method described in the present invention, the additive manufacturing comprises the following steps: laser power of 50 to 400 W; scanning rate for printing the outer contour of the printed part ...

[0015] As a preferred embodiment of the preparation method of the present invention, the gradient heat treatment comprises three stages: the first stage is to maintain the temperature at 1100-1250°C to promote grain boundary migration; the second stage is to cool the temperature to 800-950°C to stabilize the substructure; and the third stage is to air cool the material to room temperature.

[0016] As a preferred embodiment of the preparation method of the present invention, the gradient heat treatment comprises a first stage heating rate of 5 to 30°C / min and a holding time of 2 to 8 hours; a second stage heating rate of 2 to 20°C / min and a holding time of 0.5 to 5 hours.

[0017] As a preferred embodiment of the preparation method of the present invention, the pressure waveform of the pulse hot isostatic pressing is a square wave or a sine wave, and the difference between the peak pressure and the valley pressure is 50 to 150 MPa.

[0018] As a preferred embodiment of the preparation method of the present invention, the pulse hot isostatic pressing treatment temperature is 900-1200° C. and the time is 0.5-4 hours.

[0019] Beneficial effects of the present invention:

[0020] (1) The present invention improves the supercooling of the composition by adding high entropy alloy (HEA) elements such as Ti and Al, significantly refines the solidification structure, reduces the cellular structure and grain size, effectively suppresses the anisotropy of mechanical properties caused by the difference between the fine equiaxed crystals at the bottom of the molten pool and the coarse columnar crystals inside, and improves the uniformity of the grains.

[0021] (2) Cerium has strong chemical activity and can react with impurities such as oxygen and sulfur in molten steel to form stable rare earth inclusions, purifying the molten steel and reducing the formation of harmful inclusions. In the additive manufacturing process, the addition of cerium helps to optimize the fluidity of the molten pool and reduce forming defects. In addition, the addition of cerium can refine the grain size and improve the mechanical properties of the material.

[0022] (3) Titanium boride is a kind of hard material with excellent wear resistance and high temperature strength. Adding nano-ceramic particles to stainless steel can effectively improve the hardness and wear resistance of the material, and is suitable for manufacturing components in high-load and high-wear environments. Titanium boride will react with carbon in stainless steel at high temperatures to produce titanium carbide and titanium oxide, reducing the Cr content of the material during service. 23 The precipitation of C6 forms a chromium-poor area, which helps to improve the high-temperature oxidation resistance of the material and extend its service life.

[0023] (4) The addition of molybdenum helps to form a stable solid solution, enhance the high temperature performance of the material, and inhibit the abnormal growth of grains during heat treatment. It can also delay the growth of M 23 The precipitation of C6 at grain boundaries prevents Cr segregation there, improving the corrosion resistance of the stainless steel. Manganese has excellent deoxidizing properties, forming stable MnS and MnO, which purify the molten steel and reduce the impact of impurities on the 3D printing process. Manganese is a strong austenite former, which reduces the critical cooling rate of steel, helping 304L stainless steel maintain its austenitic structure and reducing the formation of delta-ferrite.

[0024] (5) The heat treatment temperature of 1100-1250℃ provides sufficient energy to drive grain boundary migration, prompting columnar crystals to transform into equiaxed crystals through recrystallization, eliminating intragranular texture. High temperature insulation can also effectively release stress and reduce subsequent deformation and cracking tendencies. In the medium temperature stage, by controlling the stability of dislocations and subgrain boundaries, dislocations are rearranged to form a stable subgrain structure, avoiding the strength loss caused by excessive grain coarsening in the high temperature stage. The air cooling strategy can avoid the γ→α' martensite transformation and maintain the austenite phase structure through a moderate cooling rate.

[0025] (6) Pulsed pressure (square wave / sine wave) promotes multi-directional plastic deformation through cyclic loading and unloading, breaking the columnar crystals and texture unique to LPBF, inducing the formation of equiaxed recrystallized grains, and significantly reducing the directional dependence of mechanical properties. Dynamic pressure fluctuations apply multi-angle compressive forces to pores and unfused defects, which are particularly effective for interlaminar defects and reduce anisotropic defect distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0027] Figure 1 This is a scanning image of the morphology of the fully dense stainless steel mixed powder produced by additive manufacturing without anisotropy, used in Example 1 of the present invention (scale bar 50 μm);

[0028] Figure 2 Metallographic image of the non-anisotropic high-performance additively manufactured fully dense stainless steel prepared in Example 1 of the present invention (scale 500 μm);

[0029] Figure 3 This is a scanning electron microscope image of the non-anisotropic high-performance additively manufactured fully dense stainless steel prepared in Example 1 of the present invention, taken along a plane parallel to the build direction (scale bar 50 μm);

[0030] Figure 4 This is a scanning electron microscope image of the non-anisotropic high-performance additively manufactured fully dense stainless steel prepared in Example 1 of the present invention, perpendicular to the build direction plane (scale 50 μm). DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0034] Unless otherwise specified, all raw materials used in the examples of the present invention are commercially available. Among them, stainless steel powder is provided by Zhongti New Materials Co., Ltd. with the product number S30406.

[0035] Description of the stainless steel testing method for this embodiment and comparative example:

[0036] Vickers hardness test: Microhardness tester (Buehler MicroMet 5104, USA)

[0037] Tensile strength test: Universal material testing machine (Shimadzu AG-Xplus 100kN)

[0038] Density: Density meter (Ohaus AR224CN, USA)

[0039] Example 1

[0040] This embodiment provides a method for preparing fully dense stainless steel by additive manufacturing to eliminate anisotropy:

[0041] The raw material composition is as follows according to mass percentage: 304L powder: 90.6%, Ti: 2.5%, Al:

[0042] 2.0%, Ce: 0.3%, TiB2: 2.1%, Mo: 1.5%, Mn: 1.0%.

[0043] Zirconia balls were added to the planetary ball mill to ensure uniform powder mixing, with a ball-to-material ratio of 1. The ball milling speed was 200 rpm and the ball milling time was 3 h. The mixed powder was used for LPBF printing.

[0044] The LPBF forming process of the above stainless steel mixed powder is as follows: laser power: 200W; scanning speed: 900mm / s; scanning spacing: 0.08mm; scanning layer thickness: 0.04mm; scanning strategy: the rotation angle between adjacent layers is 67°; substrate preheating temperature: 200℃.

[0045] The printed parts were subjected to gradient heat treatment. The first stage heat treatment temperature was 1200°C, the heating rate was 15°C / min, and the holding time was 5 hours. The second stage heat treatment temperature was 900°C, the heating rate was 10°C / min, and the holding time was 2 hours. The parts were then air-cooled to room temperature.

[0046] The pulse hot isostatic pressing treatment temperature is square, the pulse waveform is square, the average pressure is 100 MPa (peak pressure 150 MPa, valley pressure 50 MPa), the hot isostatic pressing temperature is 1100°C, and the time is 2 hours.

[0047] The metallographic examination of the final sample of Example 1 showed that Figure 1 This is a scanning image of the morphology of the fully dense stainless steel mixed powder produced by additive manufacturing without anisotropy, used in Example 1 of the present invention (scale bar 50 μm); Figure 2 Metallographic image of the non-anisotropic high-performance additively manufactured fully dense stainless steel prepared in Example 1 of the present invention (scale 500 μm); Figure 3 This is a scanning electron microscope image of the non-anisotropic high-performance additively manufactured fully dense stainless steel prepared in Example 1 of the present invention, taken along a plane parallel to the build direction (scale bar 50 μm); Figure 4 This is a scanning electron microscope image (scale 50 μm) of the non-anisotropic high-performance additively manufactured fully dense stainless steel prepared in Example 1 of the present invention, taken perpendicular to the build direction. No metallurgical defects such as cracks and delamination were found.

[0048] The density results show that the sample density is 99.8% and the average hardness of the material is 302HV 0.2 Mechanical property testing results showed that at room temperature, the yield strength perpendicular to the build direction was 580 MPa, the tensile strength was 922 MPa, and the elongation was 36.5%. The yield strength parallel to the build direction was 586 MPa, the tensile strength was 915 MPa, and the elongation was 37.0%. The strength deviation between the two groups of specimens was less than 1.2%, and the difference in elongation was less than 1.4%, demonstrating that this embodiment successfully eliminated material anisotropy while maintaining excellent mechanical properties.

[0049] Example 2

[0050] The raw material composition, in terms of mass percentage, is as follows: 304L powder: 88.6%, Ti: 3.5%, Al: 3.0%, Ce: 0.3%, TiB2: 2.1%, Mo: 1.5%, and Mn: 1.0%.

[0051] Zirconia balls were added to the planetary ball mill to ensure uniform powder mixing, with a ball-to-material ratio of 1. The ball milling speed was 200 rpm and the ball milling time was 3 h. The mixed powder was used for LPBF printing.

[0052] The LPBF forming process of the above stainless steel mixed powder is as follows: laser power: 250W; scanning speed: 800mm / s; scanning spacing: 0.1mm; scanning layer thickness: 0.04mm; scanning strategy: the rotation angle between adjacent layers is 67°; substrate preheating temperature: 200℃.

[0053] The printed parts were subjected to gradient heat treatment. The first stage heat treatment temperature was 1250°C, the heating rate was 15°C / min, and the holding time was 3 hours. The second stage heat treatment temperature was 950°C, the heating rate was 10°C / min, and the holding time was 1 hour. The parts were then air-cooled to room temperature.

[0054] The pulse hot isostatic pressing treatment temperature is square, the pulse waveform is square, the average pressure is 120 MPa (peak pressure 180 MPa, valley pressure 70 MPa), the hot isostatic pressing temperature is 1100°C, and the time is 2 hours.

[0055] Under the light microscope, there are pores inside the printed part and a small amount of cracks are observed. The density results show that the density of the printed part is 99.8% and the average hardness is 312HV. 0.2 At room temperature, the yield strength perpendicular to the construction direction is 617 MPa, the tensile strength is 951 MPa, and the elongation is 30.5%; the yield strength parallel to the construction direction is 630 MPa, the tensile strength is 895 MPa, and the elongation is 30.1%.

[0056] Example 3

[0057] The raw material composition, in terms of mass percentage, is as follows: 304L powder: 89.7%, Ti: 2.5%, Al: 2.0%, Ce: 0.3%, TiB2: 3%, Mo: 1.5%, and Mn: 1.0%.

[0058] Zirconia balls were added to the planetary ball mill to ensure uniform powder mixing, with a ball-to-material ratio of 1. The ball milling speed was 300 rpm and the ball milling time was 10 h. The mixed powder was used for LPBF printing.

[0059] The LPBF forming process of the above stainless steel mixed powder is as follows: laser power: 250W; scanning speed: 800mm / s; scanning spacing: 0.08mm; scanning layer thickness: 0.04mm; scanning strategy: the rotation angle between adjacent layers is 67°; substrate preheating temperature: 200℃.

[0060] The printed parts were subjected to gradient heat treatment. The first stage heat treatment temperature was 1200°C, the heating rate was 15°C / min, and the holding time was 5 hours. The second stage heat treatment temperature was 900°C, the heating rate was 10°C / min, and the holding time was 2 hours. The parts were then air-cooled to room temperature.

[0061] The pulse hot isostatic pressing treatment temperature is a sine wave pulse waveform, the pressure is 100 MPa (peak pressure 150 MPa, valley pressure 50 MPa), the hot isostatic pressing temperature is 1100° C., and the time is 2 hours.

[0062] Under the optical microscope, there are pores inside the printed part and a small amount of cracks are observed. The density results show that the density of the printed part is 96.8% and the average hardness is 360HV. 0.2 At room temperature, the yield strength perpendicular to the construction direction is 688MPa, the tensile strength is 1079MPa, and the elongation is 13.5%; the yield strength parallel to the construction direction is 656MPa, the tensile strength is 1082MPa, and the elongation is 17.1%.

[0063] Example 4

[0064] The raw material composition, in terms of mass percentage, is as follows: 304L powder: 90.6%, Ti: 2.5%, Al: 2.0%, Ce: 0.3%, TiB2: 2.1%, Mo: 1.5%, and Mn: 1.0%.

[0065] Zirconia balls were added to the planetary ball mill to ensure uniform powder mixing, with a ball-to-material ratio of 1. The ball milling speed was 200 rpm and the ball milling time was 3 h. The mixed powder was used for LPBF printing.

[0066] The LPBF forming process for the above stainless steel mixed powder is as follows: laser power: 200W; scanning speed: 900mm / s; scanning spacing: 0.08mm; scanning layer thickness: 0.04mm; scanning strategy: a rotation angle of 67° between adjacent layers, internal filling using 5×5mm block scanning, and adjacent blocks scanned in a perpendicular direction; substrate preheating temperature: 200℃.

[0067] The printed parts were subjected to gradient heat treatment. The first stage heat treatment temperature was 1200°C, the heating rate was 15°C / min, and the holding time was 5 hours. The second stage heat treatment temperature was 900°C, the heating rate was 10°C / min, and the holding time was 2 hours. The parts were then air-cooled to room temperature.

[0068] The pulse hot isostatic pressing treatment temperature is square, the pulse waveform is square, the average pressure is 100 MPa (peak pressure 150 MPa, valley pressure 50 MPa), the hot isostatic pressing temperature is 900°C, and the time is 4 hours.

[0069] The metallographic examination of the final sample of this embodiment showed that there were only trace pores inside it, and no metallurgical defects such as cracks and delamination were found. The density results showed that the density of the sample was 99.8%, and the average hardness of the material was 304HV. 0.2Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 625 MPa, the tensile strength is 983 MPa, and the elongation is 44.5%; the yield strength parallel to the construction direction is 603 MPa, the tensile strength is 966 MPa, and the elongation is 42.9%.

[0070] Example 5

[0071] The raw material composition, in terms of mass percentage, is as follows: 304L powder: 90.6%, Ti: 2.5%, Al: 2.0%, Ce: 0.3%, TiB2: 2.1%, Mo: 1.5%, and Mn: 1.0%.

[0072] Zirconia balls were added to the planetary ball mill to ensure uniform powder mixing, with a ball-to-material ratio of 1. The ball milling speed was 200 rpm and the ball milling time was 3 h. The mixed powder was used for LPBF printing.

[0073] The LPBF forming process of the above stainless steel mixed powder is as follows: laser power: 200W; scanning speed: 900mm / s; scanning spacing: 0.08mm; scanning layer thickness: 0.04mm; scanning strategy: the rotation angle between adjacent layers is 67°; substrate preheating temperature: 200℃.

[0074] The printed parts were subjected to gradient heat treatment. The first stage heat treatment temperature was 1250°C, the heating rate was 30°C / min, and the holding time was 2 hours. The second stage heat treatment temperature was 950°C, the heating rate was 20°C / min, and the holding time was 0.5 hours. The parts were then air-cooled to room temperature.

[0075] The pulse hot isostatic pressing treatment temperature is square, the pulse waveform is square, the average pressure is 100 MPa (peak pressure 150 MPa, valley pressure 50 MPa), the hot isostatic pressing temperature is 1100°C, and the time is 2 hours.

[0076] The metallographic examination of the final sample of Example 6 showed that there were only trace pores inside it, and no metallurgical defects such as cracks and delamination were found. The density results showed that the density of the sample was 99.2%, and the average hardness of the material was 318HV. 0.2 Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 622MPa, the tensile strength is 954MPa, and the elongation is 30.5%; the yield strength parallel to the construction direction is 635MPa, the tensile strength is 890MPa, and the elongation is 27.8%.

[0077] Example 6

[0078] To prepare anisotropy-free high-performance additively manufactured fully dense stainless steel, laser powder bed fusion (LPBF) was used to print a stainless steel mixed powder, which contained the following components by mass percentage: 304L powder: 90.6%, Ti: 2.5%, Al: 2.0%, Ce: 0.3%, TiB2: 2.1%, Mo: 1.5%, and Mn: 1.0%.

[0079] Zirconia balls were added to the planetary ball mill to ensure uniform powder mixing, with a ball-to-material ratio of 1. The ball milling speed was 200 rpm and the ball milling time was 3 h. The mixed powder was used for LPBF printing.

[0080] The LPBF forming process of the above 3D printed stainless steel mixed powder is as follows: laser power: 150W; scanning speed: 900mm / s; scanning spacing: 0.05mm; scanning layer thickness: 0.03mm; scanning strategy: a rotation angle of 67° between adjacent layers; substrate preheating temperature: 200℃.

[0081] The printed parts were subjected to gradient heat treatment. The first stage heat treatment temperature was 1100°C, the heating rate was 15°C / min, and the holding time was 4 hours. The second stage heat treatment temperature was 800°C, the heating rate was 10°C / min, and the holding time was 3 hours. The parts were then air-cooled to room temperature.

[0082] The pulse hot isostatic pressing treatment temperature is square, the pulse waveform is square, the average pressure is 100 MPa (peak pressure 150 MPa, valley pressure 50 MPa), the hot isostatic pressing temperature is 1100°C, and the time is 2 hours.

[0083] The printed part has pores under the optical microscope, but no other metallurgical defects. The density results show that the sample density is 99.5% and the average hardness of the material is 282HV. 0.2 Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 566MPa, the tensile strength is 852MPa, and the elongation is 30.1%; the yield strength parallel to the construction direction is 541MPa, the tensile strength is 851MPa, and the elongation is 31.2%.

[0084] Table 1 shows the mechanical properties of the alloys prepared in Examples 1 to 6 along different directions at room temperature.

[0085] Table 1

[0086]

[0087]

[0088] As shown in Table 1, the alloy system of the present invention has a reasonable ratio and exhibits excellent comprehensive mechanical properties (density, tensile strength, elongation, and low deviation rate of properties in different directions) under the action of distributed heat treatment and pulse pressure. The present invention also has the technical advantages of readily available raw materials, high operability and high performance.

[0089] Comparative Example 1

[0090] The difference from Example 1 is that the heat treatment is a conventional solution treatment, specifically a heat treatment temperature of 1100° C., holding for 2 hours, and then air cooling.

[0091] Comparison point: Excluding gradient heat treatment and verifying its necessity for grain uniformity.

[0092] Metallographic examination of the final sample from this comparative example revealed only pores, with no metallurgical defects such as cracks or delamination. Density testing revealed a density of 98.7% and an average hardness of 273 HV0.2. Mechanical properties testing revealed room temperature yield strength perpendicular to the build direction of 556 MPa, tensile strength of 867 MPa, and elongation of 37.5%. Parallel to the build direction of 535 MPa, tensile strength of 850 MPa, and elongation of 37.8% were also achieved.

[0093] Comparative Example 2

[0094] The difference from Example 1 is that the TiB2 nano-reinforcement phase is removed. The raw material composition is as follows, calculated by mass percentage: 304L powder: 92.7%, Ti: 2.5%, Al: 2.0%, Ce: 0.3%, Mo: 1.5%, Mn: 1.0%, and the rest is the same as Example 1.

[0095] Comparison point: Testing the effect of nanoparticles on mechanical property improvement and anisotropy suppression.

[0096] The metallographic examination of the final sample of this comparative example showed that there were only a few pores inside it, and no metallurgical defects such as cracks and delamination were found. The density results showed that the density of the sample was 99.9%, and the average hardness of the material was 198HV. 0.2 Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 438 MPa, the tensile strength is 566 MPa, and the elongation is 50.1%; the yield strength parallel to the construction direction is 435 MPa, the tensile strength is 580 MPa, and the elongation is 60.8%.

[0097] Comparative Example 3

[0098] The difference from Example 1 is that the pressure of the pulse hot isostatic pressing is changed to a constant pressure of 100 MPa without waveform fluctuation. The rest is the same as Example 1.

[0099] The metallographic examination of the final sample of this comparative example showed that there were only a few pores inside it, and no metallurgical defects such as cracks and delamination were found. The density results showed that the density of the sample was 99.1%, and the average hardness of the material was 287HV. 0.2 Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 510 MPa, the tensile strength is 709 MPa, and the elongation is 31.2%; the yield strength parallel to the construction direction is 504 MPa, the tensile strength is 696 MPa, and the elongation is 37.2%.

[0100] Comparative Example 4

[0101] The difference from Example 1 is that no metal Ti powder is added. The raw material composition, calculated by mass percentage, is as follows: 304L powder: 93.1%, Al: 2.0%, Ce: 0.3%, TiB2: 2.1%, Mo: 1.5%, Mn: 1.0%, and the rest is the same as Example 1.

[0102] The metallographic examination of the final sample of this comparative example showed that there were only a few pores inside it, and no metallurgical defects such as cracks and delamination were found. The density results showed that the density of the sample was 88.4%, and the average hardness of the material was 244HV. 0.2 Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 479 MPa, the tensile strength is 603 MPa, and the elongation is 35.6%; the yield strength parallel to the construction direction is 405 MPa, the tensile strength is 593 MPa, and the elongation is 33.1%.

[0103] Comparative Example 5

[0104] The difference from Example 1 is that no metal Al powder is added. The raw material composition, calculated by mass percentage, is as follows: 304L powder: 92.6%, Ti: 2.5%, Ce: 0.3%, TiB2: 2.1%, Mo: 1.5%, Mn: 1.0%, and the rest is the same as Example 1.

[0105] The metallographic examination of the final sample of this comparative example showed that there were only a few pores inside it, and no metallurgical defects such as cracks and delamination were found. The density results showed that the density of the sample was 99.5%, and the average hardness of the material was 239HV. 0.2 Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 455 MPa, the tensile strength is 577 MPa, and the elongation is 30.7%; the yield strength parallel to the construction direction is 440 MPa, the tensile strength is 538 MPa, and the elongation is 40.1%.

[0106] Comparative Example 6

[0107] The difference from Example 1 is that metal Ce powder is not added. The raw material composition, calculated by mass percentage, is as follows: 304L powder: 90.9%, Ti: 2.5%, Al: 2.0%, TiB2: 2.1%, Mo: 1.5%, Mn: 1.0%, and the rest is the same as Example 1.

[0108] The metallographic examination of the final sample of this comparative example showed that there were only a few pores inside it, and no metallurgical defects such as cracks and delamination were found. The density results showed that the density of the sample was 99.5%, and the average hardness of the material was 239HV. 0.2 Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 455MPa, the tensile strength is 577MPa, and the elongation is 30.7%; the yield strength parallel to the construction direction is 440MPa, the tensile strength is 477MPa, and the elongation is 46.5%.

[0109] Comparative Example 7

[0110] The difference from Example 1 is that no metal Mo powder is added. The raw material composition, calculated by mass percentage, is as follows: 304L powder: 92.1%, Ti: 2.5%, Al: 2.0%, Ce: 0.3%, TiB2: 2.1%, Mn: 1.0%, and the rest is the same as Example 1.

[0111] The metallographic examination of the final sample of this comparative example showed that there were only a few pores inside it, and no metallurgical defects such as cracks and delamination were found. The density results showed that the density of the sample was 99.6%, and the average hardness of the material was 216HV. 0.2 Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 390 MPa, the tensile strength is 507 MPa, and the elongation is 42.5%; the yield strength parallel to the construction direction is 365 MPa, the tensile strength is 538 MPa, and the elongation is 40.1%.

[0112] Comparative Example 8

[0113] The difference from Example 1 is that no metal Mn powder is added. The raw material composition, calculated by mass percentage, is as follows: 304L powder: 91.6%, Ti: 2.5%, Al: 2.0%, Ce: 0.3%, TiB2: 2.1%, Mo: 1.5%, and the rest is the same as Example 1.

[0114] The metallographic examination of the final sample of this comparative example showed that there were only a few pores inside it, and no metallurgical defects such as cracks and delamination were found. The density results showed that the density of the sample was 99.8%, and the average hardness of the material was 310HV. 0.2Mechanical properties test results show that at room temperature, the yield strength perpendicular to the construction direction is 473MPa, the tensile strength is 860MPa, and the elongation is 16.9%; the yield strength parallel to the construction direction is 558MPa, the tensile strength is 802MPa, and the elongation is 22.5%.

[0115] Table 2 shows the mechanical properties of the alloys obtained in Comparative Examples 1 to 8 along different directions at room temperature.

[0116] Table 2

[0117]

[0118]

[0119] As shown in Table 2, when some raw materials are missing from the comparative examples or certain key post-processing steps are omitted, the performance of the samples significantly deteriorates. Specifically, the absence of raw materials (such as TiB2 and Al) leads to a significant decrease in the material's density, hardness, and tensile properties; while the absence of post-processing steps such as pulse hot isostatic pressing (HIP) results in even more pronounced anisotropy in the mechanical properties. Compared to the examples, the mechanical properties of the comparative examples differ significantly, demonstrating the crucial influence of raw material integrity and post-processing on material properties.

[0120] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, and all of these should be included in the scope of the present invention.

Claims

1. An additively manufactured fully dense stainless steel with eliminated anisotropy, characterized by: Including AISI 304L powder, Ti, Al, Ce, TiB2, Mo, Mn; Calculated by mass percentage of the raw materials, the AISI 304L powder content is 85.0-95.0%, the Ti content is 1.5-3.5%, the Al content is 1.0-3.0%, the Ce content is 0.1-0.5%, the TiB2 content is 0.5-5.0%, the Mo content is 1.0-2.0%, and the Mn content is 0.5-1.5%.

2. The additively manufactured fully dense stainless steel according to claim 1, characterized in that: The AISI 304L powder has a mass percentage of 87.5-92.5%, a Ti content of 2.0-3.0%, an Al content of 1.5-2.5%, a Ce content of 0.2-0.4%, a Ti B2 content of 1.5-2.5%, a Mo content of 1.2-1.5%, and a Mn content of 0.6-1.0%.

3. The additively manufactured fully dense stainless steel according to claim 2, characterized in that: Calculated by mass percentage of the raw materials, the AISI 304L powder has an AISI 304L content of 90.6%, a Ti content of 2.5%, an Al content of 2.0%, a Ce content of 0.3%, a Ti B2 content of 2.1%, a Mo content of 1.5%, and a Mn content of 1.0%.

4. The method for preparing fully dense stainless steel by additive manufacturing according to any one of claims 1 to 3, characterized in that: The method comprises subjecting the raw materials described in claims 1 to 3 to additive manufacturing, and then subjecting the raw materials to gradient heat treatment and pulse hot isostatic pressing to obtain the additively manufactured fully dense stainless steel.

5. The preparation method according to claim 4, wherein: The raw materials are mixed in a planetary ball mill before additive manufacturing, and zirconium oxide balls are added and fully mixed, with a ball-to-material ratio of 1:1, a ball milling speed of 50 to 300 revolutions per minute, and a ball milling time of 2 to 10 hours.

6. The preparation method according to claim 4, wherein: The additive manufacturing method has a laser power of 50 to 400 W, a scanning rate of 600 to 3000 mm / s for printing the outer contour, a scanning rate of 300 to 2000 mm / s for filling the inner area, a block scanning strategy for filling the inner area, a scanning spacing of 0.05 to 0.20 mm, a scanning layer thickness of 0.03 to 0.1 mm, and a scanning strategy in which the rotation angle between adjacent layers is 0 to 90 degrees. The oxygen content is controlled below 0.2% during printing, and the substrate heating temperature is 100 to 300°C.

7. The preparation method according to claim 4, wherein: The gradient heat treatment includes three stages: the first stage is to maintain the temperature at 1100-1250°C to promote grain boundary migration; the second stage is to cool the temperature to 800-950°C to stabilize the substructure; and the third stage is to air cool to room temperature.

8. The preparation method according to claim 7, wherein: The gradient heat treatment has a first stage heating rate of 5 to 30° C. / min and a heat preservation time of 2 to 8 hours; a second stage heating rate of 2 to 20° C. / min and a heat preservation time of 0.5 to 5 hours.

9. The preparation method according to claim 4, wherein: The pressure waveform of the pulse hot isostatic pressing is a square wave or a sine wave, and the difference between the peak pressure and the valley pressure is 50 to 150 MPa.

10. The preparation method according to claim 9, wherein: The pulse hot isostatic pressing treatment temperature is 900-1200° C. and the time is 0.5-4 hours.

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