A kind of metal powder for magnetic force combination 3D printing and its preparation method

Abstract

The application provides a kind of metal powder for magnetic force combined 3D printing, the metal powder is austenitic steel metal powder, substantially non-magnetic in initial state, can produce magnetism after stress, and can recover to substantially non-magnetic again after heat treatment.The application also provides a kind of preparation method of metal powder for magnetic force combined 3D printing, including designing material composition, making martensite start transformation temperature lower than 3D printing powder laying temperature, the highest temperature of strain-induced martensitic transformation higher than 3D printing powder laying temperature, stacking fault energy greater than or equal to 18mJ / m 2 , nickel equivalent and chromium equivalent are in austenite phase region on Schaeffler diagram;According to the designed composition, melt the metal material;The melted metal is made into metal powder;Solution treatment and water quenching treatment obtain substantially non-magnetic metal powder;Make the powder produce magnetism after stress.The metal powder prepared by the application can meet the requirements of magnetic force combined 3D printing, and is easy to realize industrialized preparation.

Description

Technical Field

[0001] This invention relates to the field of 3D printing technology, specifically to a metal powder for magnetic bonding 3D printing and its preparation method. Background Technology

[0002] Additive manufacturing technology is one of the most advanced manufacturing technologies currently available, with main types including fused deposition modeling (FDM), laser additive manufacturing (LAM), electron beam fusion molding (EBDM), and binder jetting. Among these, binder jetting has been widely used in moldless casting production. However, the use of binders is costly, easily introduces porosity defects in castings, causes environmental pollution, and is difficult to clean. A novel magnetic bonding 3D printing technology uses magnetic force under a magnetic field to bond the model into a single unit, replacing or reducing the use of binders and solving the aforementioned problems. The key to realizing this new magnetic bonding 3D printing technology is the need for a powder material with selectable magnetic regions.

[0003] Currently, the most studied magnetic transformation methods are chemical doping, crystal transformation, and high-temperature oxidation. However, these methods face many difficulties in applying them to magnetically coupled 3D printing technology. There is still a need to develop a powder material that can achieve simple and efficient magnetic control in 3D printing. Metastable austenitic steel exhibits different magnetic properties depending on its microstructure. The martensite phase of a body-centered cubic (BCC) structure is ferromagnetic, while the austenite phase of a face-centered cubic (FCC) structure is paramagnetic. Under a certain driving force, the austenite phase in metastable austenitic steel can rapidly undergo a martensitic transformation, which could be developed as an efficient way to control the magnetic properties of materials. However, because research has mainly focused on avoiding phase transformations in austenitic steel to improve stability or inducing partial phase transformations to improve the mechanical properties of the material, the magnetic transformation characteristics caused by phase transformations have not yet been fully utilized.

[0004] Therefore, by adjusting the content ratio of elements such as Cr, Ni, and Mn in austenitic steel, a metastable austenitic steel powder was designed and prepared. Under a smaller driving force, more martensitic phase transformations can be achieved to generate magnetism, and after heat treatment, it can revert to the austenitic phase to achieve demagnetization. This fully utilizes the magnetic change characteristics generated by the phase transformation of austenitic steel, making it applicable to magnetic bonding 3D printing technology, which has important application value. Summary of the Invention

[0005] To address the problems of porosity defects, environmental pollution, and high cleaning difficulty caused by existing jet binder 3D printing technology when used in casting, this invention provides a metal powder for magnetic bonding 3D printing. The magnetic properties of this metal powder material can be selectively controlled, and the model can be bonded into a whole by magnetic force under a magnetic field to replace or reduce the use of binder. This invention also provides a method for preparing the metal powder for magnetic bonding 3D printing.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] On the one hand, the present invention provides a metal powder for magnetic bonding 3D printing. The metal powder is an austenitic steel metal powder that is basically non-magnetic in its initial state, can generate magnetism after being subjected to force, and can return to being basically non-magnetic after being heated.

[0008] Furthermore, the martensitic transformation initiation temperature of the austenitic steel powder is lower than the 3D printing powder laying temperature, the maximum strain-induced martensitic transformation temperature is higher than the 3D printing powder laying temperature, and the stacking fault energy is greater than or equal to 18 mJ / m. 2 The nickel and chromium equivalents are located in the austenitic phase region on the Schaeffler microstructure diagram.

[0009] On the other hand, the present invention provides a method for preparing metal powder for magnetic bonding 3D printing, comprising the following steps:

[0010] S1. Design the composition of the metallic material so that its martensite initiation temperature is lower than the 3D printing powder-laying temperature, its strain-induced martensite transformation maximum temperature is higher than the 3D printing powder-laying temperature, and its stacking fault energy is greater than or equal to 18 mJ / m 2 The nickel and chromium equivalents are located in the austenitic phase region on the Schaeffler microstructure diagram;

[0011] S2. Smelting: Smelting metallic materials according to the designed composition;

[0012] S3, Powder processing, which involves turning molten metal into metal powder;

[0013] S4. The metal powder is subjected to solid solution treatment and water quenching treatment to obtain metal powder that is basically non-magnetic.

[0014] S5. To make essentially non-magnetic metal powder magnetic when subjected to force.

[0015] Furthermore, step S1, designing the composition of the metallic material, includes the following steps:

[0016] S11. Preliminary design material composition range;

[0017] S12. Calculate the martensite initiation temperature of the material and select a composition range whose martensite initiation temperature is lower than the 3D printing powder spreading temperature.

[0018] S13. Within the composition range selected in step S12, calculate the highest temperature of strain-induced martensitic transformation of the material, and select the composition range where the highest temperature of strain-induced martensitic transformation is higher than the 3D printing powder spreading temperature.

[0019] S14. Within the composition range selected in step S13, calculate the stacking fault energy of the material, and select a stacking fault energy greater than or equal to 18 mJ / m. 2 The range of ingredients;

[0020] S15. Within the composition range selected in step S14, calculate the nickel equivalent and chromium equivalent of the material, and select the composition range in which the nickel equivalent and chromium equivalent are in the austenitic phase region on the Schaeffler microstructure diagram.

[0021] S16. Within the component range screened in step S15, calculate the chromium-nickel ratio of the material, sort the components screened in step S15 according to the chromium-nickel ratio, and select the components with the highest chromium-nickel ratio.

[0022] Furthermore, the highest temperature at which the strain-induced martensitic transformation of the material occurs in step S1 is used as... represent, That is, the temperature at which austenite undergoes a 50% martensitic transformation when the true strain is 30%; the stacking fault energy of the material in step S1 can be used as... represent, It is the stacking fault energy at room temperature (300K).

[0023] Furthermore, the martensitic transformation initiation temperature of the material is calculated as follows:

[0024]

[0025] The highest temperature at which strain-induced martensitic transformation occurs in the material is calculated as follows:

[0026]

[0027] The stacking fault energy of the material is calculated as follows:

[0028]

[0029] The nickel equivalent of the material is calculated as follows:

[0030]

[0031] The chromium equivalent of the material is calculated as follows:

[0032]

[0033] in, , , , , , , , , These represent the weight percentages of C, N, Mn, Si, Cr, Ni, Mo, Cu, and Co elements in the metal alloy, respectively. It is the stacking fault energy at room temperature (300K). It is the stacking fault energy of pure γ-Fe at room temperature.

[0034] Furthermore, the melting in step S2 is vacuum induction melting.

[0035] Furthermore, in step S3, the powder processing is performed by inert gas atomization.

[0036] Furthermore, the method for generating magnetism in the essentially non-magnetic metal powder after being subjected to force in step S5 is shot peening.

[0037] Furthermore, the spraying speed of the metal powder material subjected to shot peening / blasting is 10-160 m / s.

[0038] Compared with existing technologies, the metal powder for magnetic bonding 3D printing provided by this invention has characteristic indicators that meet the requirements of magnetic bonding 3D printing technology for powder spreading materials and is easy to achieve industrial-scale preparation. The metal powder preparation method for magnetic bonding 3D printing provided by this invention can achieve precise quantitative design of components, has strong process operability, and is easy to implement computer screening. Attached Figure Description

[0039] Figure 1 This is a flowchart of the novel magnetic bonding 3D printing production process involved in this invention.

[0040] Figure 2 This is a flowchart of a method for preparing metal powder for magnetic bonding 3D printing provided by the present invention.

[0041] Figure 3 These are materials with different compositions according to embodiments provided by the present invention. and Isotherm diagram.

[0042] Figure 4 These are stacking fault energy diagrams of materials with different compositions according to embodiments of the present invention.

[0043] Figure 5 This is a Schaeffler tissue diagram according to an embodiment of the present invention.

[0044] Figure 6 This refers to the austenitic phase region range of the material provided in the embodiments of the present invention.

[0045] Figure 7 This is a comparison diagram of the material under stress and after heat treatment provided in the embodiments of the present invention.

[0046] Figure 8This is a graph showing the changes in magnetic gravity of the material under stress and after heat treatment, provided in an embodiment of the present invention. Detailed Implementation

[0047] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific illustrations.

[0048] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "model," "magnetized," and "non-magnetic" should be interpreted broadly. For example, "non-magnetic" also includes, in engineering practice, low-magnetic properties that are nearly non-magnetic. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0049] The flowchart of the novel magnetic bonding 3D printing production process involved in this invention is as follows: Figure 1 As shown, after powdering, a selective magnetic transformation is required to make the powder material in the mold area magnetic, while the rest is non-magnetic, so that a magnetic field can be applied after layer-by-layer printing to obtain the casting model.

[0050] This invention employs an indirect method to achieve selective magnetic transformation, comprising two steps: First, pretreatment is performed before powder spreading, transforming all non-magnetic austenitic steel powder into magnetic material through a martensitic phase transformation under stress. After powder spreading, selective laser heating is used to revert the martensite back to austenite, converting non-target areas into non-magnetic regions. This invention utilizes the martensitic transformation and its reversibility in austenitic steel to achieve magnetic transformation between magnetic and non-magnetic states, offering advantages such as low cost, simplicity, and rapid transformation speed.

[0051] As a specific embodiment, the present invention provides a metal powder for magnetic bonding 3D printing. The metal powder is an austenitic steel metal powder that is basically non-magnetic in its initial state, can generate magnetism after being subjected to force, and can return to being basically non-magnetic after being heated.

[0052] The main reason is that for austenitic steel to transform from non-magnetic to magnetic, the austenitic structure needs to transform into martensite. This phase transformation can be driven by mechanical or temperature forces. If driven by temperature, a typical process is quenching, but the martensite produced in this way will revert to austenite when the temperature reaches the 3D printing powder spreading temperature, and the magnetism will disappear. If driven by mechanical force, applying stress to the material, a typical process is shot peening / blasting. The resulting martensite will not revert to austenite when the temperature reaches the 3D printing powder spreading temperature, and the magnetism will not disappear. The magnetic martensite produced by mechanical force will have the mechanical force removed during selective heat treatment, and the magnetic martensite will revert to non-magnetic austenite. This invention cleverly utilizes the difference between mechanical and temperature forces to achieve the transformation from magnetic martensite before selective heat treatment to non-magnetic austenite after selective heat treatment at the same 3D printing powder spreading temperature, thus solving the problem of magnetic selective area control in 3D printing.

[0053] In one embodiment, the martensite initiation temperature of the austenitic steel powder is lower than the 3D printing powder laying temperature, the maximum strain-induced martensite transformation temperature is higher than the 3D printing powder laying temperature, and the stacking fault energy is greater than or equal to 18 mJ / m. 2 The nickel and chromium equivalents are located in the austenitic phase region on the Schaeffler microstructure diagram.

[0054] The main reason for adopting the above-mentioned technical means is that the austenitic steel powder needs to have the following characteristics during use: during the pretreatment before powder spreading, the material needs to be transformed from non-magnetic to magnetic, so as to generate more martensite phase change under less mechanical driving force, and be able to maintain it until the 3D printing powder spreading temperature. This requires that the maximum temperature of strain-induced martensitic transformation of the material is higher than the 3D printing powder spreading temperature. During selective heat treatment of non-target areas, the material that has already undergone martensitic transformation needs to be transformed into non-magnetic, so as to obtain more inverse austenite, and be able to maintain it until the 3D printing powder spreading temperature. This requires that the temperature at which the martensitic transformation begins is lower than the 3D printing powder spreading temperature.

[0055] In one implementation, the key parameters related to martensitic phase transformation are defined and the calculation formulas used are as follows:

[0056] (1) The martensite transformation temperature in austenitic steel ( )

[0057] The physical meaning of this temperature range is the difference in free energy between the austenite and martensite phases, representing the temperature at which the minimum driving force required for the phase transformation is reached, or reflecting the minimum undercooling required for the martensitic transformation to occur. Therefore, whether austenite can transform into martensite when metastable austenitic steel is cooled to a certain temperature depends on... . This also reflects the stability of austenite. The lower the austenitic steel temperature, the higher its stability.

[0058] steel Temperature is related to many factors, including the degree of alloying, the degree of austenitization after heating and holding, and grain size. Among these, the most important influencing factor is its chemical composition. This invention uses a quantitative empirical formula established through statistical methods as one of the guiding principles for alloy design. Specifically, the martensitic transformation initiation temperature of the material is calculated as follows:

[0059]

[0060] in, , , , , , These represent the weight percentages of C, N, Mn, Si, Cr, and Ni elements in the metal alloy, respectively.

[0061] (2) The highest temperature at which strain-induced martensitic transformation occurs ( )

[0062] The physical meaning is the highest temperature at which strain-induced martensitic transformation occurs, i.e., when the temperature is higher than [a certain temperature]. At a certain temperature, no martensitic phase transformation occurs despite plastic deformation. It can also be used to determine the stability of austenite, the thermodynamic conditions for martensitic transformation at a certain temperature, and the final transformation amount of martensite.

[0063] because It is difficult to measure experimentally. Temperature point can be replaced This refers to the temperature at which austenite undergoes a 50% martensite transformation when the true strain is 30%. The higher the value, the lower the stability of the metastable austenitic steel. Whether deformation within a certain temperature range above a certain point will induce martensitic phase transformation needs to be considered in the case of austenitic steel. Temperature. To ensure that metastable austenitic steel undergoes martensitic transformation through mechanical impact treatment at the powder-laying temperature, then... The temperature should be higher than the powder-spreading temperature; to enable metastable austenitic steel to produce more martensite under relatively small mechanical driving forces, the stability of the austenite should be as low as possible. The higher the better within a suitable range. This invention selects an empirical formula for calculation. The maximum temperature of strain-induced martensitic transformation of the material is calculated as follows:

[0064]

[0065] in, , , , , , , These represent the weight percentages of C, N, Mn, Si, Cr, Ni, and Mo elements in the metal alloy, respectively.

[0066] (3) Stacking fault energy ( )

[0067] It is an important intrinsic parameter affecting austenitic phase transformation, deformation, and properties. It refers to the energy difference between atoms in stacking faults and normal stacking. It is calculated by measuring the stacking fault width and using a formula derived from dislocation theory. It reflects the strain energy caused by stacking faults and the Suzuki effect caused by the segregation of alloying elements.

[0068] The transformation sequence of strain-induced martensitic phase transformation was affected: when the parent material... Less than 18 mJ / m 2 hour, Indirect conversion The route is → → This is detrimental to improving magnetism. When the base material... Greater than or equal to 18 mJ / m 2 hour, Phase directly converted The route is →Austenitic twins→ This is beneficial for improving magnetism.

[0069] This invention selects the following empirical formula to calculate the material at room temperature. The stacking fault energy of the material is calculated as follows:

[0070]

[0071] in, It is the stacking fault energy at room temperature (300K). It is the stacking fault energy of pure γ-Fe at room temperature, approximately 0.036~0.042 mJ / m. 2 The calculated value is the median value of 0.039 mJ / m. 2The applicable alloy composition range for this formula is: Mn≤40%, Cr≤25%, Ni≤23%, Mo≤2%, Si≤4%, C+N≤0.45%, and total alloy element content≤45%. (Target composition steel) ≥18mJ / m 2 tends to produce directly Martensite.

[0072] (4) Nickel equivalent ( ) and chromium equivalent ( )

[0073] Chromium-nickel equivalent phase equilibrium is the fundamental theoretical basis for steel alloying. The compositional equivalent method measures the contribution of alloying elements to the structural stability of austenitic steel using Cr and Ni equivalents. The contribution of a particular alloying element to the stability of the matrix can be calculated by multiplying its mass percentage by the equivalent coefficient. Combined with the Schaeffler microstructure diagram, the structural stability of austenitic steel is assessed, and the microstructure is predicted. In the Schaeffler microstructure diagram, only when the Cr and Ni equivalents of the designed alloying elements fall within the austenitic phase region can a single austenitic microstructure be obtained after alloying.

[0074] If the target composition steel needs to maintain a stable austenitic structure at the powder-spreading temperature, then the following requirements must be met on the Schaeffler microstructure diagram: and It falls within the austenitic phase region; austenitic steels have lower stability, and the nickel equivalent should be as low as possible within a suitable range.

[0075] This invention uses an empirical formula to determine the stability of austenitic steel based on the minimum equivalent of nickel in the austenitic steel:

[0076]

[0077] This indicates the stability of austenite. .like Stable; if , and the medium is stable.

[0078] Composition design requires prediction of the microstructure based on the Schaeffler microstructure diagram to ensure that the steady-state microstructure of this steel is single-phase austenite. The nickel equivalent of the material is calculated as follows:

[0079]

[0080] The chromium equivalent of the material is calculated as follows:

[0081]

[0082] in, , , , , , , , , These represent the weight percentages of C, N, Mn, Si, Cr, Ni, Mo, Cu, and Co elements in the metal alloy, respectively.

[0083] (5) Chromium-nickel ratio ( )

[0084] Metastable austenitic steel, after deformation, produces a large amount of martensite. Annealing at an appropriate temperature causes the martensite to inversely transform into austenite, but the chromium-nickel ratio in the composition affects the transformation mechanism. When the chromium-nickel ratio is high, the martensite-to-austenite transformation occurs via diffusion; when the chromium-nickel ratio is low, the transformation occurs via a non-diffusional shear transformation. Shear-induced inverse transformation has a lower transformation temperature and a faster transformation rate compared to diffusional transformation. To ensure the composition meets the above conditions, the martensite inverse transformation should proceed rapidly. Therefore, a high nickel-chromium ratio is preferred in the design to achieve a phase transformation mechanism dominated by shear-induced inverse transformation.

[0085] As another specific embodiment, please refer to Figure 2 As shown, this invention provides a method for preparing metal powder for magnetic bonding 3D printing, comprising the following steps:

[0086] S1. Design the metal material composition. In this embodiment, the 3D printing powder laying temperature is 30℃, ensuring that the martensite initiation transformation temperature is lower than the 3D printing powder laying temperature, the maximum strain-induced martensite transformation temperature is higher than the 3D printing powder laying temperature, and the stacking fault energy is greater than or equal to 18mJ / m. 2 The nickel and chromium equivalents are located in the austenitic phase region on the Schaeffler microstructure diagram;

[0087] S2. Smelting: Smelting metallic materials according to the designed composition;

[0088] S3, Powder processing, which involves turning molten metal into metal powder;

[0089] S4. The metal powder is subjected to solid solution treatment and water quenching treatment to obtain metal powder that is basically non-magnetic.

[0090] S5. To make essentially non-magnetic metal powder magnetic when subjected to force.

[0091] In one embodiment, step S1, designing the composition of the metallic material, includes the following steps:

[0092] S11. Preliminary design of material composition range; In this embodiment, the preliminary design of material composition range is Cr: 16~19 wt%, Ni: 6~10 wt%, Mn: 1~2 wt%, Mo: 0.375 wt%, Si: 0.5 wt%, C: 0.075 wt%, S: 0.15 wt%, P: 0.0225 wt%.

[0093] S12. Calculate the martensite initiation temperature of the material and select a composition range where the martensite initiation temperature is lower than the 3D printing powder spreading temperature.

[0094] S13. Within the composition range selected in step S12, calculate the highest temperature of strain-induced martensitic transformation of the material, and select the composition range where the highest temperature of strain-induced martensitic transformation is higher than the 3D printing powder spreading temperature.

[0095] Figure 3 These are materials with different compositions in this embodiment. and Isotherm diagram, Figure 3 Each solid line on the chart represents a different... The isotherms and their corresponding required ranges of Cr, Ni, and Mn alloying elements. As the Mn content increases, The isotherms are constantly shifting to the left, which means that to reach... The upper limit target range (≤-30 ℃) for Cr and Ni contents available for screening is continuously expanding. Under the same Mn content, the Ni content has a significant impact on… The impact is greater. Figure 3 Each dashed line represents a different The isotherms and their corresponding required ranges of Cr, Ni, and Mn alloying elements. As the Mn content increases, The isotherms are constantly shifting to the left, which means that to reach... The lower limit target range (≥45 °C) for Cr and Ni content suitable for screening is continuously narrowing. Under the same Mn content, the Cr content has a significant impact on… The impact is greater. Figure 3 The material composition of the intersection can simultaneously satisfy <-30 ℃ and Conditions ≥45℃. Because... Point and The point increases or decreases almost simultaneously with changes in composition, when Point or The higher the value, the more unstable the austenitic steel with that composition becomes. Therefore, within a suitable range, Point and The higher the score, the better.

[0096] S14. Within the composition range selected in step S13, calculate the stacking fault energy of the material, and select a stacking fault energy greater than or equal to 18 mJ / m. 2 The range of ingredients;

[0097] Figure 4 These are stacking fault energy diagrams of materials with different compositions according to embodiments of the present invention. The materials need to be formed directly under a driving force. To minimize the formation of martensite and intermediate phases, the target composition should be selected within regions with high stacking fault energy (≥18 mJ / m). 2 And the higher the better. The calculation should cover all components within the specified range. All greater than 18 mJ / m 2 With the same Cr and Ni content, as the Mn content increases, the composition at each point... It will continue to decrease. When the Mn content is 1.0 wt%, the intersection region is the largest and the same component point is... Since it is the largest, the Mn content was selected as 1.0 wt%.

[0098] S15. Within the composition range selected in step S14, calculate the nickel equivalent and chromium equivalent of the material, and select the composition range in which the nickel equivalent and chromium equivalent are in the austenitic phase region on the Schaeffler microstructure diagram.

[0099] Figure 5 This is the Schaeffler microstructure diagram involved in the embodiments of the present invention, and the materials are calculated according to the formula. and Calculation range selection Figure 4 The Mn content is 1.0 wt% and meets the following requirements: <-30 ℃ and A rectangular intersection region with a temperature ≥45 ℃. This rectangular intersection region corresponds to... Figure 5 The area shown by the red dashed rectangle in the Schaeffler organization diagram.

[0100] S16. Within the component range selected in step S15, calculate the chromium-nickel ratio of the material and select the component with the higher chromium-nickel ratio.

[0101] Figure 6 The austenitic phase region range of the material provided in the embodiments of the present invention needs to be selected to ensure that the material maintains a single austenitic structure at room temperature.

[0102] To achieve a phase transition mechanism dominated by shear-reverse phase transition in the subsequent reverse phase transition process, under the premise of satisfying other conditions, priority should be given to those with higher Cr / Ni ratios. Figure 6 Target component region.

[0103] Calculated according to the formula Figure 6Target component region and ,all If all values ​​are less than 0, it indicates that the stability of all austenitic steels within the selected composition range tends to be metastable.

[0104] In summary, the final designed material composition ranges are as follows: Cr: 16.1~16.5 wt%, Ni: 8.7~9.1 wt%, Mn: 1.0 wt%, Mo: 0.375 wt%, Si: 0.5 wt%, C: 0.075 wt%, S: 0.15 wt%, P: 0.0225 wt%. , , , , The values ​​were -39.13℃, 48.75℃, and 51.61 mJ / m, respectively. 2 11.15%, 17.93%.

[0105] In one embodiment, the highest temperature at which the strain-induced martensitic transformation of the material occurs in step S1 is used as... represent, That is, the temperature at which austenite undergoes a 50% martensitic transformation when the true strain is 30%; the stacking fault energy of the material in step S1 can be used as... represent, It is the stacking fault energy at room temperature (300K).

[0106] In one embodiment, the melting in step S2 is vacuum induction melting, which can reduce the oxidation of alloying elements and ensure the accuracy of chemical composition.

[0107] In one embodiment, the powder processing in step S3 is inert gas atomization, which can reduce surface oxidation of the powder material, increase the flowability of the powder material, and make the preparation process mature and reliable.

[0108] In one embodiment, the method by which step S5 causes the essentially non-magnetic metal powder to become magnetic under stress is shot peening. Shot peening is a surface strengthening process widely used in existing factories. It is a cold working process that uses shot to bombard the surface of a workpiece and implant residual stress to improve the fatigue strength of the workpiece. It is widely used to improve the mechanical strength, wear resistance, fatigue resistance, and corrosion resistance of parts, and is particularly suitable for the stress processing of powdered particulate materials. Therefore, the specific process of causing initially non-magnetic particulate materials to become magnetic under stress deformation through shot peening is well known to those skilled in the art and will not be described in detail here.

[0109] In one embodiment, the shot blasting / peening treatment of the metal powder material is carried out at a velocity of 10-160 m / s, and the range of values ​​is designed to accommodate the compositional variations of metastable austenitic steel powder materials.

[0110] To better understand the technical solution provided by this invention, the following will provide further explanation with reference to specific examples.

[0111] In one aspect, the present invention provides a 0.75Cr16.3Ni8.9 steel powder for magnetic bonding 3D printing technology. The composition of this material, by mass percentage, includes: Ni: 8.9 wt%, Cr: 16.3 wt%, Mn: 1.0 wt%, Mo: 0.375 wt%, Si: 0.5 wt%, C: 0.075 wt%, S: 0.15 wt%, P: 0.0225 wt%, and other unspecified elements, each ≤0.02 wt%, totaling ≤0.10 wt%, with the remainder being Fe.

[0112] In the above technical solution, the 0.75Cr16.3Ni8.9 powder is spherical with a sphericity greater than 95%, a hollow sphere rate of no more than 3%, an oxygen content of less than 0.05%, a particle size distribution of 0.5~1mm, and a loose packing density of 4.10~4.25g / cm³. 3 The fluidity is 26.2~27.4s / 50g;

[0113] Preferably, in the above technical solution, the 0.75Cr16.3Ni8.9 steel powder is composed of an austenitic phase.

[0114] In another aspect, the present invention provides a method for preparing the above-mentioned 0.75Cr16.3Ni8.9 metastable austenitic steel powder, which first prepares the steel ingot by vacuum induction melting, and then prepares the powder using a vacuum induction melting inert gas atomization (VIGA) method. The method is characterized by the following steps:

[0115] Step 1, Smelting and Preparation: After mixing the raw materials according to the above proportions, the mixture is smelted and cast by vacuum induction melting to initially produce as-cast 0.75Cr16.3Ni8.9 austenitic steel;

[0116] Step 2: Homogenization treatment. The cast steel ingot with the riser removed and the surface oxide layer removed is homogenized to eliminate possible component segregation in the steel ingot.

[0117] Step 3: Powder processing. 0.75Cr16.3Ni8.9 austenitic steel bars are placed in a vacuum induction inert gas atomization powder making equipment to obtain pre-0.75Cr16.3Ni8.9 powder by gas atomization. Then, the pre-0.75Cr16.3Ni8.9 powder is sieved to remove large particles, and then placed in a vacuum drying oven to dry, obtaining spherical 0.75Cr16.3Ni8.9 powder.

[0118] Step 4: Solution treatment. Solution treatment is carried out in an atmosphere heating furnace, followed by water quenching.

[0119] Furthermore, in step 1, the temperature at which the molten steel is heated is 1650~1685 ℃.

[0120] Furthermore, in step 1, the smelting apparatus is a medium-frequency vacuum induction furnace.

[0121] Furthermore, in step 1, the process of crushing and mixing components is included before smelting; smelting includes pretreatment, roughing and refining processes performed in sequence.

[0122] Furthermore, in step 2, the homogenization treatment temperature is 400℃ and the time is 4h.

[0123] Furthermore, in step 3, the oxygen content is controlled to be below 600 ppm throughout the entire process.

[0124] Furthermore, in step 3, the drying temperature in the vacuum drying oven is set to 100°C, and the drying time is more than 2 hours.

[0125] Furthermore, in step 3, the obtained 0.75Cr16.3Ni8.9 powder has a particle size of 50-150µm and a sphericity of over 95%.

[0126] Furthermore, step 3 includes a final melting temperature of 1620~1635℃, a vacuum degree of less than 10 Pa, and an atomizing gas pressure of 9.0~12.5 MPa.

[0127] Furthermore, in step 3, the powder processing preparation method also includes mechanical ball milling, CNC machining, etc.

[0128] Furthermore, in step 4, the solution treatment is carried out under a protective atmosphere, the heat treatment temperature is 1050 °C, and the time is 30 min;

[0129] Furthermore, the experiment in step 4 needs to be carried out under vacuum conditions, and the protective atmosphere includes at least one of argon, helium, and nitrogen atmospheres.

[0130] Figure 7This is a comparison diagram of the material under stress and after heat treatment provided in the embodiment of the present invention, based on actual measurements. It can be seen that the material produces martensite after being subjected to stress, and the martensite reverts to austenite after heat treatment.

[0131] Figure 8 The graph shows the changes in magnetic gravity of the material after stress and heat treatment according to the embodiment of the present invention. It can be seen that the material was basically non-magnetic in the initial state, became magnetic after being subjected to stress, and returned to being basically non-magnetic after heat treatment.

[0132] Compared with existing technologies, the present invention has the following significant advantages:

[0133] 1. The metal powder characteristics prepared by this invention can meet the requirements of magnetic bonding 3D printing technology for powder spreading materials, and are easy to realize industrial preparation. This preparation technology has the application prospect of industrial preparation.

[0134] 2. The metal powder prepared by this invention, due to the design and proportion adjustment of its composition, plays a role in regulating the stability of austenite and improving the trend of martensite phase transformation, so that the powder sample has the advantage of controllable magnetic properties, which efficiently realizes the requirement of magnetic transformation of powder material in magnetic bonding 3D printing technology.

[0135] 3. The metal powder preparation method provided by the present invention can achieve precise quantitative design of components, has strong operability, and is easy to implement computer screening.

[0136] Finally, 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 it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A metal powder for magnetic bonding 3D printing, characterized in that, The metal powder is an austenitic steel powder, which is initially essentially non-magnetic, but becomes magnetic after being subjected to stress, and then returns to essentially non-magnetic after heat treatment. The martensite initiation temperature of the austenitic steel powder is lower than the 3D printing powder laying temperature, the maximum temperature of strain-induced martensite transformation is higher than the 3D printing powder laying temperature, and the stacking fault energy is greater than or equal to 18 mJ / m. 2 The nickel and chromium equivalents are located in the austenitic phase region on the Schaeffler microstructure diagram.

2. A method for preparing metal powder for magnetic bonding 3D printing, characterized in that, Includes the following steps: S1. Design the composition of the metallic material so that its martensite initiation temperature is lower than the 3D printing powder-laying temperature, its strain-induced martensite transformation maximum temperature is higher than the 3D printing powder-laying temperature, and its stacking fault energy is greater than or equal to 18 mJ / m 2 The nickel and chromium equivalents are located in the austenitic phase region on the Schaeffler microstructure diagram; S2. Smelting: Smelting metallic materials according to the designed composition; S3, Powder processing, which involves turning molten metal into metal powder; S4. The metal powder is subjected to solid solution treatment and water quenching treatment to obtain metal powder that is basically non-magnetic. S5. To make essentially non-magnetic metal powder magnetic when subjected to force.

3. The method for preparing metal powder for magnetic bonding 3D printing according to claim 2, characterized in that, Step S1, designing the composition of the metallic material, includes the following steps: S11. Preliminary design material composition range; S12. Calculate the martensite initiation temperature of the material and select a composition range whose martensite initiation temperature is lower than the 3D printing powder spreading temperature. S13. Within the composition range selected in step S12, calculate the highest temperature of strain-induced martensitic transformation of the material, and select the composition range where the highest temperature of strain-induced martensitic transformation is higher than the 3D printing powder spreading temperature. S14. Within the composition range selected in step S13, calculate the stacking fault energy of the material, and select a stacking fault energy greater than or equal to 18 mJ / m. 2 The range of ingredients; S15. Within the composition range selected in step S14, calculate the nickel equivalent and chromium equivalent of the material, and select the composition range in which the nickel equivalent and chromium equivalent are in the austenitic phase region on the Schaeffler microstructure diagram. S16. Within the component range screened in step S15, calculate the chromium-nickel ratio of the material, sort the components screened in step S15 according to the chromium-nickel ratio, and select the components with the highest chromium-nickel ratio.

4. The method for preparing metal powder for magnetic bonding 3D printing according to claim 3, characterized in that, The highest temperature at which the material undergoes strain-induced martensitic transformation in step S1 is used. represent, That is, the temperature at which austenite undergoes a 50% martensitic transformation when the true strain is 30%; the stacking fault energy of the material in step S1 can be used as... represent, It is the stacking fault energy at room temperature (300K).

5. The method for preparing metal powder for magnetic bonding 3D printing according to claim 4, characterized in that, The martensitic transformation initiation temperature of the material is calculated as follows: The highest temperature at which strain-induced martensitic transformation occurs in the material is calculated as follows: The stacking fault energy of the material is calculated as follows: The nickel equivalent of the material is calculated as follows: The chromium equivalent of the material is calculated as follows: in, , , , , , , , , These represent the weight percentages of C, N, Mn, Si, Cr, Ni, Mo, Cu, and Co elements in the metal alloy, respectively. It is the stacking fault energy at room temperature (300K). It is the stacking fault energy of pure γ-Fe at room temperature.

6. The method for preparing metal powder for magnetic bonding 3D printing according to claim 2, characterized in that, The melting in step S2 is vacuum induction melting.

7. The method for preparing metal powder for magnetic bonding 3D printing according to claim 2, characterized in that, The powder processing in step S3 is inert gas atomization.

8. The method for preparing metal powder for magnetic bonding 3D printing according to claim 2, characterized in that, The method described in step S5, which causes the essentially non-magnetic metal powder to become magnetic under stress, is shot peening.

9. The method for preparing metal powder for magnetic bonding 3D printing according to claim 8, characterized in that, The spraying speed of the metal powder material being shot blasted / peened is 10-160 m / s.

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