High-thermal-conductivity die-casting die additive manufacturing metal powder and preparation method

Abstract

The invention relates to high-thermal-conductivity die-casting die additive manufacturing metal powder and a preparation method. The high-thermal-conductivity metal powder for additive manufacturing of the die-casting die comprises the following chemical components in percentage by mass: 0.25-0.35% of C, 1t of Si, 1t of P, 1t of S, 1t of P, 1t of S, 1t of P, 1t of S and the balance of Fe and inevitable impurities. 0.1%, Mn: lt; 0.20%, Ni: lt; 3.00%, Cr: lt; 2.00%, W: 1.80-2.50%, and V: lt; the steel comprises the following components in percentage by weight: 0.1% of Fe, 2.50-3.80% of Mo, less than or equal to 0.02% of S, less than or equal to 0.025% of P, less than or equal to 0.025% of O and the balance of Fe and inevitable impurities. The metal powder has the beneficial effects that the obtained metal powder is suitable for 3D printing and is suitable for direct manufacturing of a high-load die-casting die conformal waterway insert, the application bottlenecks of existing H13 steel and 18Ni300 maraging steel in the aspects of formability, heat-conducting property and cost are solved, the forming qualification rate and heat-conducting property of an additive manufacturing inlay die are remarkably increased, the service life of the additive manufacturing inlay die is remarkably prolonged, and the metal powder is suitable for 3D printing and direct manufacturing of the high-load die-casting die conformal waterway insert. And the safety and efficient heat management requirements of the integrated die-casting die on the conformal waterway are met.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing materials technology, and particularly to metal powder for additive manufacturing of high thermal conductivity die-casting molds and its preparation method. Background Technology

[0002] Against the backdrop of global environmental degradation and climate change, countries are actively seeking paths to sustainable development. In recent years, carbon emissions from passenger vehicles have declined year by year, while the production of lightweight vehicles has steadily increased. The target aluminum content for lightweight vehicles is approximately 260 kg per vehicle, with die-cast aluminum alloys contributing >55%, and 65% of cast aluminum alloys being produced using high-pressure die casting. The mold cooling system is crucial to its lifespan, efficiency, and product quality. Its important role is manifested in increasing the solidification rate of cast alloys or injection molded parts, thereby shortening molding time, refining the casting microstructure, reducing thermal fatigue cracking, and thus extending mold life.

[0003] Traditionally manufactured molds consist of a series of straight-hole channels (point cooling), resulting in poor cooling performance. The distance between the point cooling water holes and the forming surface must be no less than 15mm. During die casting, the mold frequently comes into contact with high-temperature molten aluminum, causing the cavity surface temperature to rise rapidly and creating a significant temperature difference with the top of the cooling channels. This leads to uneven thermal expansion of the mold material, generating thermal stress. When the thermal stress exceeds the mold material's tolerance, microcracks will appear at the connection between the forming surface and the cooling channels, initially small. As the mold undergoes repeated hot and cold cycles, the repeated thermal stress causes the microcracks to gradually expand and increase. The initiation and propagation of microcracks are influenced by various factors, including material properties, temperature variation, and mechanical stress. Under the combined effect of these factors, the microcracks at the connection between the forming surface and the cooling channels become interconnected, causing mold leakage and ultimately mold failure. Furthermore, mold temperature also affects the quality of the formed parts; for example, mold temperature is second only to casting temperature in its significant impact on the formation of defects such as shrinkage and porosity in the formed parts. Uneven temperature distribution in the die casting mold often leads to local overheating or premature solidification, which in turn exacerbates the uneven distribution of shrinkage cavities and porosity, thus posing a significant challenge to the forming process.

[0004] To address the issues of poor cooling performance and easy leakage at the connection between the forming surface and the cooling channel in traditional straight-shaped machining cooling water channels for molds, it is necessary to manufacture conformal cooling channel inserts using 3D printing. Currently, the alloy powders used for additive manufacturing of die-casting molds are mainly H13 hot-work die steel and 18Ni300 maraging steel, but these have significant drawbacks: H13 is a medium-carbon steel with high crack sensitivity, easily forming microcracks during 3D printing, resulting in poor formability. Directly formed parts reach a hardness of approximately 55 HRC, exhibiting poor crack propagation. During use, crack propagation can lead to waterline rupture, posing a significant safety hazard. Compared to traditional die-casting mold steel (H13 steel, 24-26 W / mK), additive manufacturing... The thermal conductivity of H13 steel (8-18 W / mK) is also significantly reduced. 18Ni300 steel relies on high Ni (18-19%) and high Co (8.5-9.5%) for age hardening. The higher Ni content stabilizes the austenitic structure, forming a single martensitic matrix during rapid cooling after solution treatment, thus improving the fracture toughness of martensitic aging steel. Co can delay the recovery process of the martensitic matrix during high-temperature treatment, maintaining the stability of the matrix structure and ensuring that the material retains high strength and dimensional accuracy after aging. Patents CN 118792591 A and CN 109554626B also disclose designs based on high Co, Ni, and Mo compositions of 18Ni300 steel. However, the raw material cost of this type of steel is extremely high, and its thermal conductivity is less than 2 / 3 that of H13, resulting in poor thermal fatigue resistance and difficulty in meeting the requirements of high-load molds, thus limiting its application. Therefore, there is a need to develop special additive manufacturing materials with high thermal conductivity and printability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and, through optimized composition design and improved preparation methods, provide a high thermal conductivity metal powder for additive manufacturing of die-casting molds and its preparation method. This invention is suitable for 3D printing and the direct manufacturing of conformal water channel inserts for high-load die-casting molds. It solves the application bottlenecks of existing H13 steel in terms of formability and thermal conductivity, significantly improving the forming yield, thermal conductivity, and service life of additive manufacturing insert molds, and meeting the safety and efficient thermal management requirements of conformal water channels in integrated die-casting molds.

[0006] The technical approach adopted in this invention is as follows:

[0007] (1) Traditional H13 steel is a medium-carbon (0.4%) and medium-alloy steel (5%Cr-1%Mo-1%V). The strength and impact toughness of the material are adjusted by dissolving carbides during quenching and precipitating secondary carbides during tempering. However, in the 3D printing process, the laser beam locally melts the metal powder at high temperature, followed by rapid cooling. Medium and high carbon alloy steels have poor thermal conductivity (e.g., H13 steel is only 24-25 W / (m·K)), and heat easily accumulates inside the part, forming a huge temperature gradient. Repeated heating-cooling cycles between layers cause thermal stress to continuously accumulate, which can lead to cracks when the tensile strength of the material is exceeded. In addition, rapid cooling causes austenite to transform into hard and brittle martensite, accompanied by volume expansion. High carbon martensite has high inherent brittleness and is prone to microcrack initiation under residual stress. To solve this problem, the carbon content is reduced to a medium-low carbon level (significantly lower than 0.4% of H13), which reduces the brittleness of high carbon martensite and residual stress, suppresses solidification cracks, and also lowers the upper limit of the substrate preheating temperature. Reducing carbon content also improves the welding performance of the material; (2) Thermal conductivity is a key physical property of die casting mold material. Metal thermal conductivity is divided into free electron thermal conductivity and phonon thermal conductivity. At lower temperatures, free electron thermal conductivity is dominant. However, as the temperature increases, lattice vibration intensifies, the resistance of phonons to the movement of free electrons increases, electronic thermal conductivity is weakened, and phonon thermal conductivity becomes dominant. The thermal conduction of metal is mainly caused by the migration of free electrons, and therefore has a direct relationship with resistivity. At low concentrations, the effect of solute atoms on the resistivity of the metal matrix is ​​related to the difference in the outer electron structure of solute and matrix atoms. Si and Cr have the strongest effect on thermal conductivity. Si exists in steel in the form of solid solution, and its outer electron structure is quite different from that of iron atoms. Si significantly reduces thermal conductivity. When the mass fraction of Si increases from 0.1 to 0.3, the thermal conductivity decreases by 4 W / (m·K). In addition, increasing the content of Mn by 0.1 will lead to a decrease in the thermal diffusivity by 30 (10 -3 cm 2 ·s -1 ); Strong carbide elements Mo and W have little effect on the thermal conductivity of steel. Therefore, it is necessary to reduce the content of elements such as Si, Mn, and Cr to improve thermal conductivity; (3) H13 steel is rich in Cr and M 23 C6 or M7C3 carbides, especially spherical M 23 C6 carbides tend to aggregate and coarsen, resulting in poor thermal stability. When the Cr content is reduced and the Mo content is increased, independently nucleated MC and M2C7 carbides precipitate in dislocation regions and are less prone to aggregation and growth, effectively improving tempering softening properties and thermal fatigue resistance. W is a high-melting-point alloying element; adding W to tool and die steels significantly improves hot strength. The precipitation of M2C-type carbides from strengthening phases Mo and W is beneficial to thermal stability. Therefore, appropriately increasing the Mo and W content improves thermal stability. Through the combination of these effects, a high thermal conductivity metal powder chemical composition for additive manufacturing of die-casting molds is obtained.

[0008] The use of hypersonic gas laminar flow atomization pulverization technology effectively controls the particle size of metal powder and improves the sphericity of the powder; the use of protective hypersonic gas two-phase flow cooling technology effectively controls the increase in oxygen content of metal powder and reduces the phenomenon of metal powder agglomeration.

[0009] Based on the above objectives and overall technical solution, the specific technical solution of this invention is as follows:

[0010] A high thermal conductivity die-casting mold additive manufacturing metal powder, wherein the metal powder comprises, by mass percentage, the following chemical composition: C: 0.25-0.35%, Si: <0.1%, Mn: <0.20%, Ni: <3.00%, Cr: <2.00%, W: 1.80-2.50%, V: <0.1%, Mo: 2.50-3.80%, S: ≤0.02%, P≤0.025%, O≤0.025%, with the remainder being Fe and unavoidable impurities.

[0011] Preferably, the metal powder has the following chemical composition range: C: 0.28-0.32%, Mn: <0.10%, Ni: <2.50%, Cr: <0.1%, W: 1.90-2.10%, Mo: 2.80-3.20%.

[0012] The present invention discloses a method for preparing metal powder for additive manufacturing of high thermal conductivity die-casting molds, comprising the following process and steps:

[0013] (1) Mix the alloy raw materials according to the above mass percentages;

[0014] (2) Remove the oxide layer on the metal surface by mechanical grinding, pickling or electrolytic treatment to prevent impurities from entering the melt and affecting the purity of the powder;

[0015] (3) Place the pretreated alloy raw material from step (2) into the induction melting crucible, with a filling density of 80% to 90% of the raw material volume to prevent overflow during melting;

[0016] (4) Before melting, a vacuum must be drawn with a vacuum degree ≤1×10-3Pa and argon gas must be introduced;

[0017] (5) The pressure in the melting chamber and atomizing chamber is reduced to ≤1Pa, and the molten steel is transferred from the melting chamber to the atomizing chamber;

[0018] (6) The intermediate ladle is heated by high frequency graphite heating to reduce temperature loss and ensure that the molten steel melt temperature is ≥1650℃, the gas storage tank pressure is ≥24Mpa, the pressure regulating device is increased to ≥24Mpa, the ring hole gas jet cold atomization technology is adopted, the atomizing gas pressure is ≥10MPa, the nitrogen gas after being sprayed through the nozzle is in the form of supersonic gas-liquid two-phase flow, realizing hypersonic gas laminar flow atomization pulverization, effectively controlling the particle size of metal powder, improving the sphericity of powder, and reducing the phenomenon of metal powder agglomeration.

[0019] It also includes step (7), where the diameter of the metal powder guide nozzle is 4mm to 5.2mm, the satellite ball removal device is turned on, and the cyclone powder collection valve below the atomization chamber is turned on to ensure the sphericity of the powder in the powder collection chamber.

[0020] It also includes step (8), in which the metal powder obtained in step (7) is mechanically vibrated and sieved, and the particle size of the sieved metal powder is in the range of 15 to 53 μm.

[0021] Preferably, in step (1), the alloy raw material is a refined master alloy of EAF / MF+LF+VD, and the initial raw material has low levels of harmful elements such as oxygen and sulfur, which improves the cleanliness of the metal powder.

[0022] Preferably, in step (5), the gas in the atomizing pack is argon.

[0023] The roles and proportions of each element in the steel of this invention are based on the following, where "%" in the following description represents "mass percentage":

[0024] Carbon (C): The carbon content in steel determines the matrix hardness of quenched steel. Part of the carbon in the steel enters the steel matrix, causing solid solution strengthening, while another part combines with carbide-forming elements in the alloy to form alloy carbides. In this invention, the carbon content is reduced to a low-to-medium carbon level (0.25–0.35%) (significantly lower than the 0.4% of H13), reducing the brittleness and residual stress of high-carbon martensite, suppressing solidification cracks, effectively reducing the crack sensitivity of 3D printing, and also lowering the upper limit of the substrate preheating temperature (using the metal powder of this invention, the upper limit of the substrate preheating temperature is reduced from 200°C–250°C for traditional H13 steel to 120°C–150°C, effectively reducing the maintenance cost of 3D printing equipment). Reducing the carbon content also improves the weldability of the material. The carbon content of the steel in this invention is controlled at 0.25–0.35%, preferably 0.28–0.32%.

[0025] Nickel (Ni): Ni expands the γ-phase region, improves austenite stability, delays martensite transformation, and reduces phase transformation stress, thereby preventing cold cracking after the material contacts the substrate and improving toughness. Furthermore, the high Ni composition design allows the material to achieve the same hardness, strength, and mechanical properties after quenching and tempering through simple stress-relief annealing after 3D printing solidification, achieving the goal of eliminating the need for post-processing. Since Ni reduces the thermal conductivity of alloy steel through solid solution distortion and electron scattering, its content in the steel of this invention should be strictly controlled to <3.00%, preferably <2.50%.

[0026] Chromium (Cr): Chromium can replace iron atoms in cementite to form alloyed cementite or form alloyed carbides with C, thus stabilizing the carbides. At high temperatures, chromium combines with oxygen to form a dense Cr2O3 oxide film, effectively isolating oxygen and corrosive media, significantly delaying high-temperature oxidation and liquid metal erosion on the mold surface. In addition, chromium enhances high-temperature strength and wear resistance, and improves hardenability. However, Cr has a significant impact on thermal conductivity in steel. To minimize the reduction in thermal conductivity caused by Cr, the Cr content in the steel of this invention is controlled at <2.00%. To further improve the thermal conductivity of the material, Cr <0.10% is preferred.

[0027] Vanadium (V): Vanadium can reduce the overheating sensitivity of steel. Small amounts of vanadium can refine the steel grains, and when MC-type carbides are dispersed and precipitated through appropriate heat treatment, it mainly improves the wear resistance and strength of die steel, but reduces impact toughness. In the steel of this invention, the vanadium content is controlled at <0.10%.

[0028] Molybdenum (Mo): Molybdenum is a strong carbide-forming element. In steel, it can improve the hardenability of the steel and form special carbides, thereby improving the secondary hardening ability and wear resistance of the steel. The steel of this invention has a higher Mo content than H13 steel to compensate for the strength reduction caused by the low carbon chromium content. In the steel of this invention, the Mo content is controlled at 2.50-3.80%, preferably 2.80-3.20%.

[0029] Tungsten (W): Tungsten's role is similar to that of molybdenum, but it is superior to molybdenum in improving wear resistance. However, excessive addition reduces toughness. Considering the effective use of resources and the reduction of material costs, the steel of this invention adopts an alloying approach with Mo as the main element and W as the auxiliary element to compensate for the strength reduction caused by low carbon chromium content. In the steel of this invention, the tungsten content is controlled at 1.80-2.50%, preferably 1.90-2.10%.

[0030] Manganese (Mn): Manganese has a solid solution strengthening effect in steel, thereby improving the strength and hardness of tool steel and improving the hardenability of steel. It can also eliminate the harmful effects of sulfur. In this invention, the Mn content is controlled at <0.20%, preferably <0.10%.

[0031] Silicon (Si): As an alloying element in steel, silicon exists in solid solution form within ferrite or austenite, without forming carbides, thus improving hardenability. However, excessive silicon content significantly affects the material's thermal conductivity. This invention's steel, compared to H13 steel, significantly reduces the Si content, playing a crucial role in improving both thermal conductivity and toughness. The silicon content in this invention's steel is controlled to <0.1%.

[0032] Oxygen (O): Excessive oxygen content leads to the formation of numerous non-deformable inclusions, resulting in decreased alloy toughness and reduced fatigue performance. Oxygen content is a harmful element that must be controlled in 3D printing metal powder. Since current equipment cannot completely eliminate oxygen enrichment, the preferred alloy raw material is an EAF / MF+LF+VD refined master alloy to maintain low levels of harmful elements such as oxygen in the initial raw materials, thereby improving the cleanliness of the metal powder. The oxygen content of the steel in this invention is ≤0.025%, and more preferably ≤0.020%.

[0033] Sulfur (S): Sulfur readily combines with manganese in steel to form non-metallic inclusions MnS. This should be minimized as metallurgically as possible. During gas atomization, the S content in the steel remains essentially unchanged. Therefore, the preferred alloy raw material is an EAF / MF+LF+VD refined master alloy to maintain low levels of harmful elements such as sulfur in the initial raw materials. The sulfur content in the steel of this invention is no higher than 0.020%, preferably ≤0.003%.

[0034] Phosphorus (P): Phosphorus segregates at grain boundaries during heating at the austenitizing temperature, significantly increasing the brittleness of steel. The phosphorus content should be controlled below 0.025%, preferably below 0.015%, and the lower the content, the better.

[0035] The implementation of this invention has the following technical effects:

[0036] Based on the alloy system design and powder preparation process of this invention, the yield of fine powder in the 15-53 μm range reaches over 28%, which can effectively reduce the cost of preparing die-casting mold steel powder. Simultaneously, it exhibits high loose packing density (>3.75 g / cm³). 3 High tap density (>4.7 g / cm³) 3 The material exhibits excellent flowability (<17s / 50g), playing a crucial role in the subsequent 3D printing of high-performance molded parts. Using the metal powder of this invention, the upper limit of the substrate preheating temperature is reduced from 200℃~250℃ for traditional H13 steel to 120℃~150℃, effectively lowering the maintenance costs of 3D printing equipment. The material's thermal conductivity is improved by more than 1.8 times and 2.3 times compared to H13 steel and 18Ni300, respectively. Attached Figure Description

[0037] Figure 1Microscopic morphology of metal powder additively manufactured using a low-cost, high thermal conductivity die-casting mold, as shown in this embodiment of the invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the embodiments and accompanying drawings. It should be noted that the described embodiments are only intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0039] Example 1

[0040] This embodiment describes a method for preparing high thermal conductivity die-casting mold additive manufacturing metal powder, comprising the following steps:

[0041] (1) Mix the alloy raw materials by mass percentage. The composition of the alloy raw materials is shown in Table 1.

[0042] Preferably, the alloy raw material is a refined master alloy of EAF / MF+LF+VD, and the initial raw material has low levels of harmful elements such as oxygen and sulfur, which improves the cleanliness of the metal powder.

[0043] (2) Remove the oxide layer on the metal surface by mechanical grinding, pickling or electrolytic treatment to prevent impurities from entering the melt and affecting the purity of the powder;

[0044] (3) Place the pretreated alloy raw material from step (2) into the induction melting crucible, filling it to 85% of the raw material volume to prevent overflow during melting.

[0045] (4) Before melting, a vacuum must be drawn with a vacuum degree ≤1×10-3Pa and argon gas must be introduced;

[0046] (5) The pressure in the melting chamber and the atomizing chamber is reduced to ≤1Pa. The molten steel is transferred from the melting chamber to the atomizing package. The gas in the atomizing package is argon. Specifically, the molten steel in the melting chamber is transferred to the atomizing chamber through the intermediate ladle. Powdering is completed in the atomizing chamber by nitrogen atomization and other operations.

[0047] (6) The intermediate ladle is heated by high frequency graphite heating to reduce temperature loss and ensure that the molten steel is 1650℃ when it is smelted and exits the furnace. The pressure of the gas storage tank is 24Mpa and the pressure regulating device is increased to 24Mpa. The ring hole gas jet cold atomization technology is adopted, and the atomizing gas pressure is 10MPa. The nitrogen gas sprayed out through the nozzle is in the form of a supersonic gas-liquid two-phase flow, realizing hypersonic gas laminar flow atomization pulverization, effectively controlling the particle size of metal powder, improving the sphericity of powder, and reducing the phenomenon of metal powder agglomeration.

[0048] (7) The diameter of the metal powder guide nozzle is 5.2mm. Turn on the satellite ball removal device and turn on the cyclone powder collection valve below the atomization chamber to ensure the sphericity of the powder in the powder collection chamber.

[0049] (8) The metal powder obtained is subjected to mechanical vibration sieving, and the particle size range of the sieved metal powder is 15-53 μm.

[0050] Example 2

[0051] This embodiment describes a method for preparing high thermal conductivity die-casting mold additive manufacturing metal powder, comprising the following steps:

[0052] (1) Mix the alloy raw materials by mass percentage. The composition of the alloy raw materials is shown in Table 1.

[0053] Preferably, the alloy raw material is a refined master alloy of EAF / MF+LF+VD, and the initial raw material has low levels of harmful elements such as oxygen and sulfur, which improves the cleanliness of the metal powder.

[0054] (2) Remove the oxide layer on the metal surface by mechanical grinding, pickling or electrolytic treatment to prevent impurities from entering the melt and affecting the purity of the powder;

[0055] (3) Place the pretreated alloy raw material from step (2) into the induction melting crucible, filling it to 80% of the raw material volume to prevent overflow during melting;

[0056] (4) Before melting, a vacuum must be drawn with a vacuum degree ≤1×10-3Pa and argon gas must be introduced;

[0057] (5) The pressure in the melting chamber and the atomizing chamber is reduced to ≤1Pa. The molten steel is transferred from the melting chamber to the atomizing package. The gas in the atomizing package is argon. Specifically, the molten steel in the melting chamber is transferred to the atomizing chamber through the intermediate ladle. Powdering is completed in the atomizing chamber by nitrogen atomization and other operations.

[0058] (6) The intermediate ladle is heated by high frequency graphite heating to reduce temperature loss and ensure that the molten steel melt exiting the furnace at 1660℃. The pressure of the gas storage tank is 25Mpa, and the pressure regulating device is increased to 25Mpa. The ring hole gas jet cold atomization technology is adopted, and the atomizing gas pressure is 10MPa. The nitrogen gas sprayed out through the nozzle is in the form of a supersonic gas-liquid two-phase flow, realizing hypersonic gas laminar flow atomization pulverization, effectively controlling the particle size of metal powder, improving the sphericity of powder, and reducing the phenomenon of metal powder agglomeration.

[0059] (7) The diameter of the metal powder guide nozzle is 4.6mm. Turn on the satellite ball removal device and turn on the cyclone powder collection valve below the atomization chamber to ensure the sphericity of the powder in the powder collection chamber.

[0060] (8) The metal powder obtained is subjected to mechanical vibration sieving, and the particle size range of the sieved metal powder is 15-53 μm.

[0061] Example 3

[0062] This embodiment describes a method for preparing high thermal conductivity die-casting mold additive manufacturing metal powder, comprising the following steps:

[0063] (1) Mix the alloy raw materials by mass percentage. The composition of the alloy raw materials is shown in Table 1.

[0064] Preferably, the alloy raw material is a refined master alloy of EAF / MF+LF+VD, and the initial raw material has low levels of harmful elements such as oxygen and sulfur, which improves the cleanliness of the metal powder.

[0065] (2) Remove the oxide layer on the metal surface by mechanical grinding, pickling or electrolytic treatment to prevent impurities from entering the melt and affecting the purity of the powder;

[0066] (3) Place the pretreated alloy raw material from step (2) into the induction melting crucible, filling it to 90% of the raw material volume to prevent overflow during melting;

[0067] (4) Before melting, a vacuum must be drawn with a vacuum degree ≤1×10-3Pa and argon gas must be introduced;

[0068] (5) The pressure in the melting chamber and the atomizing chamber is reduced to ≤1Pa. The molten steel is transferred from the melting chamber to the atomizing package. The gas in the atomizing package is argon. Specifically, the molten steel in the melting chamber is transferred to the atomizing chamber through the intermediate ladle. Powdering is completed in the atomizing chamber by nitrogen atomization and other operations.

[0069] (6) The intermediate ladle is heated by high frequency graphite heating to reduce temperature loss and ensure that the molten steel is 1650℃ when it is smelted and exits the furnace. The pressure of the gas storage tank is 24Mpa and the pressure regulating device is increased to 24Mpa. The ring hole gas jet cold atomization technology is adopted, and the atomizing gas pressure is 10MPa. The nitrogen gas sprayed out through the nozzle is in the form of a supersonic gas-liquid two-phase flow, realizing hypersonic gas laminar flow atomization pulverization, effectively controlling the particle size of metal powder, improving the sphericity of powder, and reducing the phenomenon of metal powder agglomeration.

[0070] (7) The diameter of the metal powder guide nozzle is 4mm. Turn on the satellite ball removal device and turn on the cyclone powder collection valve below the atomization chamber to ensure the sphericity of the powder in the powder collection chamber.

[0071] (8) The metal powder obtained is subjected to mechanical vibration sieving, and the particle size range of the sieved metal powder is 15-53 μm.

[0072] Table 1. Statistical table of chemical composition (mass%) for Examples 1 to 3

[0073]

[0074] Table 2. Statistical table of measured particle size distribution of metal powders in Examples 1 to 3.

[0075]

[0076] Table 3. Statistical table of metal powder flowability and bulk density results from Examples 1 to 3.

[0077]

[0078]

[0079] As shown in Table 2, the D10, D50, and D90 of the die-casting mold steel powder in this embodiment can be used for formation using SLM (Selective Laser Melting) technology. Simultaneously, the yield of fine powder in the 15–53 μm range reached 28.77%, significantly reducing production costs. Table 3 presents the flowability and bulk density test results of the metal powders obtained in Examples 1–3. As shown in the table, the powder has excellent flowability and high powder spreading performance. Figure 1 The microstructure of the powder from the examples is shown. As can be seen from the figures, the powder from the examples has a high surface smoothness and few hollow particles. Overall, the mold steel metal powder from the examples exhibits good SLM printing performance.

[0080] The metal powder obtained in Example 1 was used to produce an alloy via SLM additive manufacturing. The substrate preheating temperature for SLM additive manufacturing was 135°C, which effectively reduced the maintenance cost of the 3D printing equipment. The alloy samples prepared using selective laser melting technology, after stress-relief annealing, showed the following thermal conductivity as shown in Table 4. Compared with H13 steel and 18Ni300, the thermal conductivity was increased by more than 1.8 times and 2.3 times, respectively.

[0081] Table 4. Comparison of thermal conductivity between the alloy prepared in Example 1 and existing steel grades.

[0082]

[0083] In summary, this invention provides a high thermal conductivity metal powder for additive manufacturing of die-casting molds and its preparation process. Through a comprehensive and innovative design combining master alloy composition design, smelting, and powder preparation processes, the metal powder possesses excellent overall physical properties and can be used in SLM technology within the field of laser additive manufacturing.

[0084] 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 the scope of protection of the present invention. 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 essence and scope of the technical solutions of the present invention.

Claims

1. A high thermal conductivity die-casting mold for additive manufacturing of metal powder, characterized in that, The metal powder comprises, by mass percentage, the following chemical composition: C: 0.25–0.35%, Si: <0.1%, Mn: <0.20%, Ni: <3.00%, Cr: <2.00%, W: 1.80–2.50%, V: <0.1%, Mo: 2.50–3.80%, S: ≤0.02%, P: ≤0.025%, O: ≤0.025%, with the remainder being Fe and unavoidable impurities.

2. The additive manufacturing of metal powder using a high thermal conductivity die-casting mold according to claim 1, characterized in that: The metal powder has the following chemical composition ranges: C: 0.28–0.32%, Mn: <0.10%, Ni: <2.50%, Cr: <0.1%, W: 1.90–2.10%, Mo: 2.80–3.20%.

3. The additive manufacturing of metal powder using a high thermal conductivity die-casting mold according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix the alloy raw materials according to the mass percentage; (2) Remove the oxide layer on the metal surface by mechanical grinding, pickling or electrolytic treatment to prevent impurities from entering the melt and affecting the purity of the powder; (3) Place the pretreated alloy raw material from step (2) into the induction melting crucible, with a filling density of 80% to 90% of the raw material volume to prevent overflow during melting; (4) Before melting, a vacuum must be drawn with a vacuum degree ≤1×10-3Pa and argon gas must be introduced; (5) The pressure in the melting chamber and atomizing chamber is reduced to ≤1Pa, and the molten steel is transferred from the melting chamber to the atomizing chamber; (6) The intermediate ladle is heated by high frequency graphite heating to reduce temperature loss and ensure that the molten steel melt temperature is ≥1650℃, the gas storage tank pressure is ≥24Mpa, the pressure regulating device is increased to ≥24Mpa, the ring hole gas jet cold atomization technology is adopted, the atomizing gas pressure is ≥10MPa, the nitrogen gas after being sprayed through the nozzle is in the form of supersonic gas-liquid two-phase flow, realizing hypersonic gas laminar flow atomization pulverization, effectively controlling the particle size of metal powder, improving the sphericity of powder, and reducing the phenomenon of metal powder agglomeration.

4. The additive manufacturing of metal powder using a high thermal conductivity die-casting mold according to claim 3, characterized in that: It also includes step (7), where the diameter of the metal powder guide nozzle is 4mm to 5.2mm, the satellite ball removal device is turned on, and the cyclone powder collection valve below the atomization chamber is turned on to ensure the sphericity of the powder in the powder collection chamber.

5. The additive manufacturing of metal powder using a high thermal conductivity die-casting mold according to claim 3, characterized in that: It also includes step (8), in which the metal powder obtained in step (7) is mechanically vibrated and sieved, and the particle size of the sieved metal powder is in the range of 15 to 53 μm.

6. The additive manufacturing of metal powder using a high thermal conductivity die-casting mold according to claim 3, characterized in that: In step (1), the alloy raw material is a refined master alloy of EAF / MF+LF+VD.

7. The additive manufacturing of metal powder using a high thermal conductivity die-casting mold according to claim 3, characterized in that: In step (5), the gas in the atomizing pack is argon.

8. The additive manufacturing of metal powder using a high thermal conductivity die-casting mold according to claim 3, characterized in that: The loose bulk density of the prepared metal powder is >3.75 g / cm³. 3 Tap density > 4.7 g / cm³ 3 Flowability <17s / 50g.

9. The additive manufacturing of metal powder using a high thermal conductivity die-casting mold according to claim 3, characterized in that: The obtained metal powder was used to produce an alloy through SLM additive manufacturing.

10. The additive manufacturing of metal powder using a high thermal conductivity die-casting mold according to claim 3, characterized in that: Thermal diffusivity is 0.1548 cm⁻¹ 2 / s, with a thermal conductivity of up to 62W / m·k.

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