3D printing die steel and preparation method thereof

Abstract

The invention relates to 3D printing die steel and a preparation method thereof, and belongs to the technical field of metal materials. The 3D printing die steel is prepared from the following components in percentage by mass: 0.2 to 0.4 weight percent of C, 2 to 7 weight percent of Cr, 1.5 to 5.0 weight percent of Ni, 3.0 to 7.0 weight percent of Co, 0 to 3.0 weight percent of Mo, 0 to 1.0 weight percent of V, 0 to 1.0 weight percent of Si, 0 to 1.0 weight percent of Nb, 0 to 2 weight percent of Al, 0 to 1.0 weight percent of Ti, 0 to 1.0 weight percent of Cu, 0 to 1.0 weight percent of Mn and the balance of Fe and other inevitable impurities, and the martensite transformation temperature Ms point is controlled to be 280 to 330 DEG C. The preparation method comprises the steps of smelting, gas atomization powder preparation, selective laser melting 3D printing, heat treatment, post-treatment and the like, wherein the post-treatment comprises ultrasonic rolling treatment and salt bath nitriding oxidation treatment. The 3D printing die steel provided by the invention has excellent mechanical properties and corrosion resistance, and can be widely applied to the field of high-performance die manufacturing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of 3D printing, in particular to a 3D printing die steel and a preparation method thereof. BACKGROUND

[0002] Die steel is a special steel material used to manufacture various dies, which has high hardness, high strength, high wear resistance and good thermal stability. With the development of manufacturing industry, the performance requirements of die steel are becoming higher and higher, especially in the manufacturing of complex structure dies, the traditional die steel manufacturing process has been difficult to meet the demand. In recent years, 3D printing technology (additive manufacturing) has been widely used in die manufacturing due to its advantages of being able to manufacture complex shape parts, shorten production cycle and reduce manufacturing cost.

[0003] At present, 3D printing die steel mainly includes hot work die steel and cold work die steel. Hot work die steel is mainly used for die manufacturing in high temperature environment, such as die casting die, hot forging die, etc.; cold work die steel is mainly used for die manufacturing in normal temperature or low temperature environment, such as stamping die, plastic die, etc. In the research of 3D printing die steel, H13 steel, 18Ni300 maraging steel, Corrax stainless steel, etc. are commonly used materials. These materials are prepared into spherical powder by gas atomization method, and then formed by selective laser melting (SLM) or direct metal laser sintering (DMLS) and other 3D printing technologies.

[0004] CN116334491B discloses a die steel prepared by 3D printing technology, which is mainly prepared by atomizing H13 steel powder with alloy additives, and the alloy additives are vanadium nitride with an average particle size of 20-200nm, titanium nitride, aluminum nitride, etc. In this way, the defect of relatively poor mechanical properties of 3D printed H13 die steel is overcome. CN116103567A discloses a high mirror corrosion-resistant die steel, 3D printing powder and preparation method, which is designed with low C and low Mn to reduce the crack sensitivity in the 3D printing process; by adding appropriate amount of Ni, Al and Cu, the prepared parts after 3D printing are supplemented with appropriate heat treatment process, which can precipitate Ni3Al, Ni3Cu and δCu nano particles, and play the role of precipitation strengthening.

[0005] CN118222933A discloses a hot work die steel powder for additive manufacturing and a preparation method thereof, the alloying elements in the powder are as follows in mass percentage: W(C): 0.25-0.45%, W(Cr): 4.5-5.5%, 2.0%≤W(Mo)≤0.54W(Cr) and the like, the die steel prepared from the powder has low cost, good printing effect, high density, tensile strength ≥1600MPa, elongation ≥13%, and hardness ≥48HRC. CN117987730A provides a hot work die steel easy to be additive manufactured, which comprises C 0.12-0.26%, Cr 4.5-5.8%, Mo 0.8-1.5% and the like in mass percentage, the mechanical properties are improved by forming carbide and introducing β-NiAl phase and / or Cu-rich phase; reducing the contents of C and Si not only improves the strength-ductility / toughness ratio, avoids the cracking tendency during additive manufacturing, but also improves the thermal conductivity and service life.

[0006] CN119614994A discloses a super high-strength high-toughness ultra-fine structure hot work die steel and a preparation method thereof, the die steel comprises the following components in mass percentage: C: 0.30-0.45%, Cr: 3.0-4.5%, Mo: 0.8-1.5%, V: 0.80-1.20% and the like, the martensite structure is ultra-fined by the organization regulation of conventional equipment and production process, and the strength of the hot work die steel is significantly improved.

[0007] However, the existing 3D printing die steel still has some technical problems: first, the traditional die steel is prone to generate large residual stress during 3D printing due to the characteristics of rapid cooling and heating, which leads to stress cracking and limits the printing size of the workpiece; second, the anti-tempering and anti-cracking performance of the commonly used 3D printing materials such as 18Ni300 is much lower than that of the traditional hot work die steel, which cannot meet the demand of high-temperature working environment; third, some die steel powders for 3D printing on the market such as 18Ni300 and Corrax have high content of precious elements, which leads to high cost of powder raw materials and limits its wide application; fourth, the die steel powders such as S136 and 420 have high carbon content, which has the risk of cracking during laser 3D printing, affecting the printing quality and yield; finally, the existing materials have low thermal conductivity, which affects the cooling efficiency of the die and the production efficiency.

[0008] Therefore, it is urgent to develop a new type of 3D printing die steel material which can not only meet the requirements of 3D printing process, but also has excellent comprehensive performance and moderate cost to meet the needs of modern die manufacturing industry. SUMMARY

[0009] In order to solve the problems of large residual stress, easy cracking, high cost, insufficient thermal performance and low thermal conductivity coefficient of the existing 3D printing die steel material, the present application provides a kind of 3D printing die steel and its preparation method.

[0010] The technical scheme adopted by the present application to solve its technical problems is to provide a kind of 3D printing die steel, its chemical composition includes, by weight percentage: carbon (C): 0.2-0.4wt%, chromium (Cr): 2-7wt%, nickel (Ni): 1.5-5.0wt%, cobalt (Co): 3-7.0wt%, molybdenum (Mo): 0-3.0wt%, vanadium (V): 0-1.0wt%, silicon (Si): 0-1.0wt%, niobium (Nb): 0-1.0wt%, aluminum (Al): 0-2wt%, titanium (Ti): 0-1.0wt%, copper (Cu): 0-1.0wt%, manganese (Mn): 0-1.0wt%, the balance is iron (Fe) and unavoidable impurities, at the same time, the martensite transformation temperature Ms point of the die steel is controlled in 280-330℃, to adapt to the thermal cycle working condition of rapid cooling and rapid heating in the process of laser selective melting (SLM) and other 3D printing, to avoid the cracking problem caused by incomplete transformation of the structure and accumulation of residual austenite.

[0011] The present application introduces cobalt, nickel, chromium, molybdenum, vanadium, niobium and other elements in the alloy system, and cooperates to design the content interval, replaces the medium entropy alloy system characterized by high Ni or high Cu in the prior art, and is also different from the traditional die steel design idea mainly with Fe-Cr-Mo, the innovation of the element combination in composition control not only can realize no quenching but direct tempering strengthening after 3D printing, but also the material has excellent thermal conductivity, high temperature strength and toughness and anti-cracking property, specifically, the principle of the above composition design of the present application is as follows: The present application realizes the comprehensive optimization of the performance of the die steel under the condition of 3D printing through the precise regulation and control of the alloy composition. Carbon element is one of the core elements affecting the strength and hardness of die steel, but if the content is too high, it is easy to cause lattice distortion in martensite phase, which leads to significant increase of residual stress in the printing process, affecting the size accuracy of the final forming; and if the carbon content is too low, it is difficult to form enough amount of carbide, thereby weakening the high temperature stability of the material. Therefore, the carbon content is controlled in a reasonable interval of 0.2-0.4wt% to balance the strength, hardness and printing stress.

[0012] Chromium element has excellent high temperature oxidation resistance, especially suitable for hot working environment such as die casting, can form a dense oxide film on the surface of steel, and improve the oxidation life. At the same time, chromium can also improve the hardenability, which is helpful to improve the subsequent heat treatment performance. However, excessive chromium may generate M 23C7 type carbide, instead of being detrimental to the high temperature performance of the material. Therefore, the chromium content in the present application is set to 2-7wt% to achieve the optimal balance of performance.

[0013] The introduction of nickel can effectively improve the stacking fault energy of the matrix, promote the activation of cross-slip mechanism, thereby enhancing the plasticity and toughness of the material under stress, and effectively relieving the risk of cracks caused by thermal stress during printing.

[0014] Cobalt as a strengthening solid solution element has a significant effect on improving strength and toughness at high temperatures, and can inhibit the recovery behavior of dislocations in the matrix, while promoting the stable precipitation of carbides in the grain boundary region. Such carbides have good coherency with the parent phase, not only do not impair toughness, but also enhance high temperature performance.

[0015] Molybdenum and vanadium form high-temperature stable carbides by forming carbon, providing pinning sites at the grain boundaries, strengthening the secondary hardening ability of the material, and significantly improving its temper resistance. This mechanism is crucial for the stability of the mold under high temperature and high pressure periodic service conditions.

[0016] In addition, trace elements such as niobium and titanium can significantly refine austenite grains, avoid grain coarsening during printing and heat treatment, and improve the overall toughness and dimensional stability of the material. These elements have good synergistic strengthening effect with SLM (selective laser melting) process, which can significantly improve the density and service reliability of the printed part.

[0017] In summary, the 3D printed mold steel of the present application is comprehensively controlled by the above-mentioned alloying elements, and the martensite transformation temperature (Ms point) is strictly controlled at 280-330℃. The mold steel can achieve complete martensite transformation during 3D printing, without the need for quenching to obtain excellent mechanical properties, greatly simplifying the post-processing process and improving the consistency and production efficiency of the parts.

[0018] Preferably, the chemical composition of the 3D printed mold steel includes, by weight percentage: C: 0.2-0.3wt%, Cr: 3.0-5.0wt%, Ni: 2.0-3.0wt%, Co: 4.0-6.0wt%, Mo: 2.0-3.0wt%, V: 0.5-1.0wt%, Si: 0.3-1.2wt%, Nb: 0.5-1.0wt%, Al: 0-1.5wt%, Ti: 0-0.5wt%, Cu: 0-0.1wt%, Mn: 0-0.1wt%, and the balance is Fe and unavoidable impurities.

[0019] Compared with the prior art, the above preferred technical scheme of the present application further controls the carbon content in the range of 0.2-0.3wt%, effectively balancing the residual stress in the 3D printing process and the required mechanical strength after printing; the chromium content is set to 3-5wt%, not only ensuring good oxidation resistance at high temperature, but also enhancing the hardenability during post-processing; the synergistic effect of nickel and cobalt can improve the crack resistance and thermal fatigue performance of the material by adjusting the stacking fault energy and grain boundary structure, especially suitable for the working condition requirements of high-temperature die casting molds; in addition, molybdenum and vanadium form high-temperature stable carbides, which play a secondary hardening and microstructure pinning role, significantly improving the temper resistance; the niobium and titanium elements can refine the austenite grains, improve the strength and toughness of the material after heat treatment, and effectively reduce the tendency of grain coarsening, especially suitable for realizing 3D printing of large mold parts; the addition of trace amounts of copper and manganese optimizes the composition stability, further improves the thermal conductivity and strengthens the comprehensive organizational performance.

[0020] Compared with the prior art, the 3D printing die steel and the above preferred scheme of the present application first systematically unify the "printability", "hot working performance", "heat treatment simplification" and "thermal conductivity efficiency" of the 3D printing die steel in the same alloy system through the synergistic design of the above multi-element alloy, especially by precisely controlling the Ms point in the range of 280-330℃, which can realize martensite structure without additional quenching after printing, effectively avoiding thermal stress cracks, and significantly reducing energy consumption and post-processing cost. The above technical features have obvious synergistic correlation, which constitutes an important basis for the substantial progress of the present application.

[0021] Further, the present application also provides a preparation method of the above 3D printing die steel, comprising the following steps: S1: Melting: Put the raw materials into a vacuum induction heating furnace, control the vacuum degree to be between 10 -3 to 10 -4 Pa, the melting temperature is 1550-1650℃, and the melting time is 2-3 hours to form a uniform alloy liquid; S2: Gas atomization powdering: atomize the alloy liquid through a gas atomization device to obtain alloy powder with a particle size of 15-53μm; S3: 3D printing: use a selective laser melting device to layer by layer melt and form the alloy powder; S4: Heat treatment: temper the formed die steel, the tempering temperature is 400-650℃, and the cooling method is air cooling or furnace cooling to obtain a 3D printing die steel.

[0022] Compared with existing technologies, the 3D printing mold steel proposed in this application has the following advantages: This invention optimizes the traditional mold steel production process of casting, forging, machining, and heat treatment into an integrated process of "precise composition design + powder metallurgy + additive manufacturing + simplified heat treatment," significantly improving the material's performance compatibility with 3D printing processes. By combining vacuum melting with gas atomization powder production, impurity content and compositional uniformity are effectively controlled, ensuring the compactness of the forming process during printing. Furthermore, by incorporating Ms-point controlled compositional design, the material can directly form a martensitic structure during SLM printing, eliminating the need for quenching and allowing the target strength, toughness, and thermal stability to be obtained through tempering, simplifying the post-processing steps. In addition, compared to traditional H13 or 18Ni300 steel, this invention achieves a coordinated balance of thermal conductivity, tempering resistance, and toughness through a composite alloy system, making it particularly suitable for manufacturing large-size molds in high-temperature, high-speed hot working environments. This overcomes problems such as printing cracking, uneven microstructure, and unstable performance caused by high carbon content or element mismatch in traditional mold steels. Therefore, the synergistic optimization between the preparation process and the material composition not only solves the key technical bottlenecks such as large residual stress and easy cracking, but also significantly improves the printing efficiency and service reliability of the mold, demonstrating the significant technological progress and practical value of this invention in the field of 3D printing mold steel.

[0023] Specifically, in the smelting stage, this invention employs a vacuum induction heating furnace for smelting operations. By precisely controlling the vacuum level, smelting temperature, and holding time within the furnace, it ensures that all elements in the alloy are fully melted and uniformly mixed, effectively suppressing the introduction of impurities and thus improving the purity and overall uniformity of the alloy composition. In the gas atomization powder preparation stage, this invention further regulates the pressure of high-pressure argon gas and the flow rate of the alloy liquid to stably obtain alloy powder with a particle size distribution between 15 and 53 μm. Powder within this particle size range exhibits excellent flowability and spreading performance, enabling good interlayer fusion and laser melting effects during 3D printing, significantly improving the density and dimensional accuracy of the printed parts. During 3D printing, by setting appropriate laser power, scanning speed, powder thickness, and substrate preheating temperature, the powder material melts and solidifies layer by layer, gradually building a mold blank with complex geometry and a dense structure. After printing, the molded part undergoes optimized tempering heat treatment, controlling specific temperature ranges and tempering times to eliminate residual stress caused by rapid thermal cycling, adjust the microstructure, and ultimately achieve excellent strength, hardness, and high-temperature stability, meeting the mold's service requirements under hot working conditions.

[0024] Preferably, in step S2, the conditions for powder production by the gas atomizing device are: high-pressure argon gas is used as the atomizing gas, and the argon gas pressure is 3-5 MPa, and the alloy liquid flow rate is 5-10 kg / min.

[0025] Compared with existing technologies, the above-mentioned technical solution can significantly improve the sphericity and particle size distribution of powder particles. By using high-pressure inert gas to form strong shear turbulence at the alloy liquid outlet, the metal droplets are rapidly cooled and broken into spherical particles with uniform particle size, avoiding the formation of oxide inclusions. This further yields spherical powder with good flowability, high density, and suitability for 3D printing, improving the printing quality and internal compactness of the material, effectively avoiding printing defects and porosity, and enhancing the mechanical properties and consistency of the finished product.

[0026] Preferably, in step S3, the printing parameters for the layer-by-layer melting and forming are: laser power 200-300W, scanning speed 800-1200mm / s, powder thickness 30-50μm, and substrate temperature 150-250℃.

[0027] Compared with existing technologies, the above parameter combination enables precise control of laser energy input and molten pool stability. This preferred method ensures complete powder melting without overheating through moderate energy density (matching laser power and scanning speed). Combined with thin-layer powder spreading and substrate preheating, it effectively reduces interlayer stress gradients, guaranteeing high density, excellent surface quality, and uniform microstructure in the printed parts. Simultaneously, it suppresses warping and cracking tendencies, making it particularly suitable for printing thermally stress-sensitive alloy systems such as the mold steel described in this invention, thus improving the printing stability and dimensional accuracy of complex mold structures.

[0028] Preferably, in step S4, the tempering process is performed in 2-3 tempering cycles, with each tempering cycle lasting 2-3 hours.

[0029] Compared with existing technologies, the multi-stage tempering heat treatment strategy can more fully release the residual stress accumulated during the 3D printing process. This preferred method performs multiple temperings under relatively mild heat treatment conditions, which helps stabilize the martensitic structure, promotes the dispersed precipitation of strengthening phases, and prevents coarsening of the structure or decrease in toughness caused by a single high-temperature treatment. It improves the material's resistance to tempering softening, maintains high hardness, and enhances fracture toughness and thermal stability. It is particularly suitable for hot work dies that operate under high-frequency thermal cycling loads, extending their service life and simplifying the quenching process in traditional processes.

[0030] Furthermore, after step S4 is completed, the following steps are also included: S5: Post-processing S51: Ultrasonic rolling treatment is performed on tempered 3D printing mold steel. S52: The 3D printing mold steel is subjected to preheating treatment, salt bath nitriding treatment, salt bath oxidation treatment, secondary oxidation treatment and oiling treatment in sequence to complete the preparation.

[0031] Compared with existing technologies, the above-mentioned post-processing techniques (including ultrasonic rolling, salt bath nitriding, oxidation, and oiling) can systematically improve the surface quality and service stability of 3D printing mold steel. Ultrasonic rolling induces plastic deformation to strengthen the surface structure, followed by preheating, salt bath nitriding, salt bath oxidation, secondary oxidation, and oiling. This not only forms a reinforced nitriding layer and a dense oxide film on the material surface, but also effectively improves fatigue resistance, corrosion resistance, and high-temperature friction stability. Consequently, it significantly enhances the overall service performance of the mold steel under high temperature, high pressure, and high-frequency thermal cycling, extending its service life and reducing subsequent maintenance and replacement costs. Preheating dries the moisture on the workpiece surface, preventing the workpiece from entering the nitriding furnace with water and causing danger. It also prevents cold workpieces from directly entering the nitriding furnace, which would lower the furnace temperature too much, playing a significant role in reducing deformation and improving the appearance. Preferably, in step S51, the processing parameters of ultrasonic rolling include: ultrasonic amplitude of 5-10 μm, static pressure of 600-1000 N, and ultrasonic frequency of 30 kHz.

[0032] Compared with existing technologies, the ultrasonic rolling processing parameters of 5–10 μm ultrasonic amplitude, 600–1000 N static pressure, and 30 kHz ultrasonic frequency can achieve plastic deformation and strengthening of microscopic surface structures. Moreover, the ultrasonic rolling parameters of this invention work synergistically with alloying elements, including Nb, V, and Ti, which provide strengthening phases. Ultrasonic shaping induces surface recrystallization and strengthening, achieving coordinated development of surface hardening and toughness, rather than simply increasing hardness. Under the combined action of high-frequency vibration and a certain static load in the above-mentioned preferred method, dislocation slip and accumulation occur in the surface lattice of the material, inducing micro-nano-level recrystallization structures, forming residual compressive stress zones, increasing surface hardness and inhibiting crack initiation. Without introducing heat input, it effectively reduces the surface roughness and stress concentration of printed parts, improves the fatigue strength, wear resistance, and the combined effect of subsequent nitriding / oxidation treatment of the material, and provides a reliable guarantee for the high-precision service of hot-working molds.

[0033] Preferably, in step S52, the conditions for the preheating treatment, salt bath nitriding treatment, salt bath oxidation treatment, secondary oxidation treatment, and oiling treatment include: preheating to 250~380℃ and holding for 10~30 min; salt bath nitriding treatment: holding at 520-580℃ for 10-180 min; salt bath oxidation treatment: holding at 360-430℃ for 10-30 min; secondary oxidation treatment: holding at 400℃ for 10-30 min; and oiling treatment: immersing the sample in 20-40 g machine oil.

[0034] Compared with existing technologies, the multi-stage treatment combination of "nitriding-oxidation-re-oxidation-oiling" not only optimizes the nitrided layer structure but also enhances the surface's oxidation resistance and corrosion resistance. In this process, salt bath nitriding is first performed at 520–580℃ to form a high-hardness nitride phase and diffusion layer, providing a uniform interface foundation for subsequent oxidation. Next, salt bath oxidation is performed at 360℃ to form a uniform oxide film on the surface, while simultaneously decomposing residual cyanide ions and removing toxic residues. A second oxidation is then performed at 400℃ to replenish the oxide film lost during polishing. Finally, a hydrophobic and rust-preventive protective layer is formed by oil coating. This effectively avoids stress concentration in the surface oxide film, improving surface stability and durability, making it suitable for long-term service in complex geometric molds. Furthermore, the secondary oxidation and surface pretreatment steps of this invention perfectly combine with the oxidation stabilization mechanism of Cr- and V-rich elements in the alloy, resulting in a denser oxide film with lower residual tensile stress, significantly improving corrosion resistance and thermal cycling life, exhibiting excellent synergistic effects.

[0035] Preferably, in step S52, the step of cooling cleaning and surface polishing is further included between the salt bath oxidation treatment and the secondary oxidation treatment, including: Cooling and cleaning: The 3D printing mold steel, after salt bath oxidation treatment, is air-cooled at room temperature to make the nitrided layer structure more uniform and dense, while promoting the increase of the diffusion layer depth and effectively decomposing cyanide ions (CN) remaining on the sample surface. - ; Surface polishing: Polishing the surface of the 3D printing mold steel removes any loose layers that may form on the surface, reducing the risk of tensile stress in the oxide film during subsequent secondary oxidation, thereby improving the material's corrosion resistance.

[0036] Compared with existing technologies, the above-mentioned preferred method adds a cooling cleaning and surface polishing step between salt bath oxidation and secondary oxidation, which can significantly optimize the quality of subsequent surface structure formation. The cooling cleaning promotes densification of the nitrided layer in an air-cooled environment and removes residual CN. - Sufficient hydrolysis and decomposition occur, avoiding side reactions during subsequent oxidation; while surface polishing can effectively remove the loose layer or oxide scale that may be formed during the oxidation process, avoiding uneven oxide film thickness or the formation of crack sources, thereby reducing the risk of cracking caused by oxidation tensile stress. Ultimately, a high-quality, low-defect oxide film structure is achieved, effectively improving the stability and service life of the mold in high humidity and corrosive environments. Attached Figure Description

[0037] Figure 1 The image shows the three-dimensional wear morphology of sample No. 1. Figure 2 The image shows the three-dimensional wear morphology of sample No. 2. Figure 3 The image shows the three-dimensional wear morphology of sample No. 3. Figure 4 This is a two-dimensional wear morphology diagram of sample No. 1; Figure 5 The image shows the two-dimensional wear morphology of sample No. 2. Figure 6 The image shows the two-dimensional wear morphology of sample No. 3. Figure 7 The friction coefficient curves for samples 1–3 are shown. Figure 8 The wear track depth profile curves for samples 1–3 are shown. Detailed Implementation

[0038] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of this application and are not intended to limit the scope of protection of the embodiments of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0039] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0040] This invention provides a 3D printing mold steel, which, by weight ratio, comprises: C: 0.2-0.4wt%, Cr: 2-7wt%, Ni: 1.5-5.0wt%, Co: 3.0-7.0wt%, Mo: 0-3.0wt%, V: 0-1.0wt%, Si: 0-1.0wt%, Nb: 0-1.0wt%, Al: 0-2wt%, Ti: 0-1.0wt%, Cu: 0-1.0wt%, Mn: 0-1.0wt%, with the balance being Fe and other unavoidable impurities. The martensitic transformation temperature Ms of the 3D printing mold steel is controlled at 280-330℃.

[0041] As a preferred embodiment, the 3D printing mold steel comprises, by weight ratio: C: 0.2-0.3wt%, Cr: 3.0-5.0wt%, Ni: 2.0-3.0wt%, Co: 4.0-6.0wt%, Mo: 2.0-3.0wt%, V: 0.5-1.0wt%, Si: 0.3-1.2wt%, Nb: 0.5-1.0wt%, Al: 0-1.5wt%, Ti: 0-0.5wt%, Cu: 0-0.1wt%, Mn: 0-0.1wt%, with the balance being Fe and other unavoidable impurities.

[0042] The present invention also provides a method for preparing the 3D printing mold steel, comprising the following steps: S1: Melting: Place the raw materials into a vacuum induction heating furnace and control the vacuum level at 10. -3 Up to 10 -4 Between Pa, the melting temperature is 1550-1650℃, and the melting time is 2-3 hours to form a uniform alloy liquid; S2: Gas atomization powder making: The alloy liquid is made into powder by passing it through a gas atomization device to obtain alloy powder with a particle size of 15-53μm; S3: 3D printing: using a selective laser melting device to melt the alloy powder layer by layer to form a shape; S4: Heat treatment: Temper the mold steel after forming at a temperature of 400-650℃ and cool it by air cooling or furnace cooling to obtain 3D printing mold steel.

[0043] As a preferred embodiment, in step S2, the powder-making conditions of the gas atomizing device are as follows: high-pressure argon is used as the atomizing gas, and the argon pressure is 3-5 MPa, and the flow rate of the alloy liquid is 5-10 kg / min.

[0044] As a preferred embodiment, in step S3, the printing parameters for the layer-by-layer melting and forming are: laser power 200-300W, scanning speed 800-1200mm / s, and powder thickness 30-50μm.

[0045] As a preferred embodiment, in step S4, the tempering process is performed under the following conditions: 2-3 tempering processes are conducted, and each tempering process lasts for 2-3 hours.

[0046] As a preferred embodiment, after step S4 is completed, the method further includes: S5: Post-processing S51: Ultrasonic rolling treatment is performed on tempered 3D printing mold steel. S52: The 3D printing mold steel is subjected to preheating treatment, salt bath nitriding treatment, salt bath oxidation treatment, secondary oxidation treatment and oiling treatment in sequence to complete the preparation.

[0047] As a preferred embodiment, in step S51, the processing parameters of ultrasonic rolling include: ultrasonic amplitude of 5-10 μm, static pressure of 600-1000 N, and ultrasonic frequency of 30 kHz.

[0048] As a preferred embodiment, in step S52, the conditions for the preheating treatment, salt bath nitriding treatment, salt bath oxidation treatment, secondary oxidation treatment, and oiling treatment include: preheating to 250~380℃ and holding for 10~30 min; salt bath nitriding treatment: holding at 520-580℃ for 10-180 min; salt bath oxidation treatment: holding at 360-430℃ for 10-30 min; secondary oxidation treatment: holding at 400℃ for 10-30 min; and oiling treatment: immersing the sample in 20-40# machine oil.

[0049] As a preferred embodiment, step S52 further includes a cooling cleaning and surface polishing step between the salt bath oxidation treatment and the secondary oxidation treatment, including: Cooling and cleaning: The 3D printing mold steel, after salt bath oxidation treatment, is air-cooled at room temperature to make the nitrided layer structure more uniform and dense, while promoting the increase of the diffusion layer depth and effectively decomposing cyanide ions (CN) remaining on the sample surface. - ; Surface polishing: Polishing the surface of the 3D printing mold steel removes any loose layers that may form on the surface, reducing the risk of tensile stress in the oxide film during subsequent secondary oxidation, thereby improving the material's corrosion resistance.

[0050] The beneficial effects of the 3D printing mold steel obtained by this invention are as follows: (1) Cost control advantages Compared to some carbon-free or high-nickel SLM mold steel alloy systems, this invention significantly reduces the use of expensive alloying elements, especially through optimized nickel and cobalt content, while maintaining necessary strength and thermal stability, effectively lowering raw material costs. Furthermore, since no quenching treatment is required after printing, the energy and time costs of the heat treatment process are further reduced.

[0051] (2) Excellent hot working performance Thanks to the synergistic design of multiple elements and the control of crystal structure, the material of this invention exhibits good stability, tempering resistance and crack resistance in high-temperature environments, which can meet the service requirements of mold steel under extreme working conditions such as die casting and hot extrusion, and significantly improve the reliability and service life of molds.

[0052] (3) Simplified heat treatment process By controlling a higher martensitic transformation temperature, the printing process can obtain a martensitic structure, eliminating the need for the quenching and hardening process required for traditional mold steel. After printing, only multiple tempering processes are needed to obtain the ideal structure and properties, significantly improving production efficiency and dimensional control accuracy.

[0053] (4) Large-size printing is less prone to cracking This invention reduces the carbon balance generated by residual stress, strengthens the grain refinement mechanism, and regulates alloy toughness, enabling mold steel to have stronger structural integrity during 3D printing, significantly suppressing the tendency to crack due to thermal stress accumulation, and supporting the integrated printing of larger mold parts.

[0054] (5) Significantly improves thermal conductivity Through elemental synergistic optimization design, such as introducing appropriate amounts of Cu and controlling the content of Si and Mo, the material of this invention has a thermal conductivity that is 3-4 times higher than that of conventional 3D printing mold steel. It can complete the mold cooling process more efficiently, shorten the molding cycle, and improve manufacturing efficiency, and has extremely high application value in high-frequency injection molding, die casting and other fields.

[0055] This invention optimizes the performance of 3D printing mold steel by precisely controlling the mass percentage of each alloying element. The carbon content is limited to the range of 0.2–0.4 wt% to balance the control of printing strength, hardness, and residual stress; the chromium content is set to 2–7 wt% to effectively improve the material's oxidation resistance at high temperatures and its hardenability after heat treatment; while the scientific synergy of elements such as nickel, cobalt, molybdenum, and vanadium plays a key role in improving toughness, enhancing high-temperature strength and toughness, and achieving secondary hardening, respectively. Meanwhile, the martensitic transformation temperature Ms is precisely controlled between 330 and 280°C to ensure that the microstructure can be completely transformed into martensite during the printing process, thereby avoiding the quenching step in traditional heat treatment and further improving the simplicity of the process and dimensional stability. From raw material preparation to final molding, this invention establishes a highly optimized preparation process: in the melting stage, by controlling the vacuum degree, temperature and holding time, the alloy components are ensured to be fully fused, with high purity and uniform composition; in the gas atomization process, by adjusting the atomization pressure and liquid flow rate, spherical powder with a particle size of 15–53 μm is obtained, which greatly improves the uniformity of powder spreading and melting density; in the 3D printing stage, appropriate laser power, scanning speed, powder spreading thickness and substrate temperature are set to ensure the stability and structural integrity of layer-by-layer molding; finally, in the heat treatment stage, multiple tempering operations are performed to effectively release residual stress and adjust the microstructure, so that the finished product has excellent mechanical properties and thermal stability.

[0056] The present invention will now be described in detail with reference to the embodiments: Example 1 In this embodiment, the 3D printing mold steel specifically comprises the following components by mass percentage: C: 0.25%, Cr: 4.2%, Ni: 2.5%, Co: 5.0%, Mo: 2.5%, V: 0.8%, Si: 0.6%, Nb: 0.8%, Al: 1.0%, Ti: 0.3%, Cu: 0.05%, Mn: 0.05%, with the balance being Fe and other unavoidable impurities. This composition ratio results in a martensitic transformation temperature (Ms) of 305°C for the 3D printing mold steel, falling within the ideal range of 280-330°C.

[0057] The method for preparing this 3D printing mold steel includes the following steps: S1: First, accurately weigh each element raw material according to the design ratio, including high-purity iron, high-purity carbon, metallic chromium, metallic nickel, metallic cobalt, metallic molybdenum, metallic vanadium, metallic silicon, metallic niobium, metallic aluminum, metallic titanium, metallic copper, and metallic manganese.

[0058] Next, the weighed raw materials are placed in a vacuum induction melting furnace and melted under argon protection. The melting temperature is controlled between 1550-1650℃, and the melting time is 2 hours to ensure that all elements are fully fused.

[0059] S2: The powder is prepared by gas atomization, with high-purity argon as the atomization medium, atomization pressure of 4.0 MPa, and atomization temperature of 1600℃.

[0060] S3: Subsequently, the obtained alloy powder is loaded into a 3D printing device for selective laser melting and forming. The 3D printing parameters are set as follows: laser power 200-300W, scanning speed 800-1200mm / s, scanning spacing 0.08-0.12mm, and layer thickness 0.02-0.04mm. During the printing process, the forming chamber is filled with high-purity argon gas, the oxygen content is controlled below 100ppm, and the platform preheating temperature is 150-200℃.

[0061] S4: After printing, the 3D printed part undergoes heat treatment. Heat treatment: The mold steel after molding is tempered at a temperature of 550℃ and cooled by air cooling to obtain the 3D printing mold steel. The tempering conditions are: two tempering treatments, each lasting 2 hours.

[0062] S5: Post-processing S51: Ultrasonic rolling treatment is performed on the tempered 3D printing mold steel. The ultrasonic rolling processing parameters include: ultrasonic amplitude of 5μm, static pressure of 600N, and ultrasonic frequency of 30kHz. S52: The 3D printing mold steel is subjected to preheating treatment, salt bath nitriding treatment, salt bath oxidation treatment, secondary oxidation treatment, and oiling treatment in sequence to complete the preparation. Specific treatment conditions are as follows: Preheating: Preheat to 250℃ and hold for 10 minutes; Salt bath nitriding treatment: hold at 520℃ for 10 minutes; Salt bath oxidation treatment: hold at 360℃ for 10 minutes; Between the salt bath oxidation treatment and the secondary oxidation treatment, a cooling cleaning and surface polishing step was also performed: Cooling and cleaning: The 3D printing mold steel, after salt bath oxidation treatment, is air-cooled at room temperature to make the nitrided layer structure more uniform and dense, while promoting the increase of the diffusion layer depth and effectively decomposing cyanide ions (CN) remaining on the sample surface. - ; Surface polishing: Polishing the surface of the 3D printing mold steel removes any loose layers that may form on the surface, reducing the risk of tensile stress in the oxide film during subsequent secondary oxidation, thereby improving the material's corrosion resistance. Secondary oxidation treatment: hold at 400℃ for 10 minutes; Oiling treatment: Immerse the sample in 30# machine oil.

[0063] After performance testing, the 3D printing mold steel exhibits the following characteristics: hardness of 52 HRC, tensile strength of 1800 MPa, yield strength of 1600 MPa, elongation at break of 8%, and impact toughness of 15 J / cm². 2 Even at high temperatures (650℃), this mold steel maintains good hardness (42HRC) and resistance to thermal fatigue.

[0064] In a preferred embodiment, the composition of the 3D printing mold steel can be adjusted to: C: 0.28%, Cr: 4.5%, Ni: 2.8%, Co: 5.5%, Mo: 2.8%, V: 0.9%, Si: 0.8%, Nb: 0.9%, Al: 1.2%, Ti: 0.4%, Cu: 0.08%, Mn: 0.08%, with the balance being Fe and other unavoidable impurities. This optimized formulation increases the martensitic transformation temperature Ms of the mold steel to 315℃, further improving its heat resistance and thermal fatigue resistance.

[0065] By adjusting the contents of elements such as C, Cr, Ni, and Co, the martensitic transformation temperature (Ms point) can be precisely controlled. Increasing the C content lowers the Ms point, while increasing the Co content raises it. In this embodiment, the Ms point is stabilized within the ideal range by rationally proportioning the C and Co contents. The addition of Cr, Mo, and V elements mainly improves the wear resistance and high-temperature strength of the steel, while Ni element improves the toughness of the steel. Nb and Ti elements form fine carbides, playing a role in grain refinement and precipitation strengthening.

[0066] This 3D printing mold steel is particularly suitable for making molds for high-temperature working environments such as hot work molds, die casting molds, and extrusion molds. It has excellent heat resistance, wear resistance, high-temperature strength, and thermal fatigue resistance, which can significantly extend the service life of molds and improve production efficiency.

[0067] Example 2 This embodiment provides a method for preparing 3D printing mold steel, which is similar to the method for preparing 3D printing mold steel described in Embodiment 1, but differs in the specific preparation process parameters.

[0068] The 3D printing mold steel prepared in this embodiment has the same composition as in Example 1, including the following components by mass percentage: C: 0.25%, Cr: 4.2%, Ni: 2.5%, Co: 5.0%, Mo: 2.5%, V: 0.8%, Si: 0.6%, Nb: 0.8%, Al: 1.0%, Ti: 0.3%, Cu: 0.05%, Mn: 0.05%, with the balance being Fe and other unavoidable impurities.

[0069] The method for preparing the 3D printing mold steel includes the following steps: S1: Melting: Place the weighed raw materials according to the above proportions into a vacuum induction heating furnace, and control the vacuum degree at 10. -3 Up to 10 -4 Between Pa, the melting temperature is 1600℃, the melting time is 2.5 hours, and a uniform alloy liquid is formed; S2: Gas atomization powder production: The alloy liquid is atomized using a gas atomization device to obtain alloy powder with a particle size of 15-53μm. The conditions for gas atomization powder production are: high-pressure argon gas is used as the atomizing gas, the argon gas pressure is 4.5MPa, and the alloy liquid flow rate is 8kg / min; S3: 3D Printing: Utilizing a selective laser melting system to melt alloy powder layer by layer to form a 3D model. The printing parameters for layer-by-layer melting are: laser power 250W, scanning speed 1000mm / s, and powder thickness 40μm. S4: Heat Treatment: The molded mold steel is tempered at 550℃ using air cooling to obtain 3D printing mold steel. The tempering conditions are: three tempering treatments, each lasting 2.5 hours.

[0070] After completing the above steps, this embodiment also performs the following post-processing steps: S5: Post-processing S51: Ultrasonic rolling treatment is performed on the tempered 3D printing mold steel. The processing parameters for ultrasonic rolling include: ultrasonic amplitude of 8μm, static pressure of 800N, and ultrasonic frequency of 30kHz. S52: The 3D printing mold steel is subjected to preheating treatment, salt bath nitriding treatment, salt bath oxidation treatment, secondary oxidation treatment, and oiling treatment in sequence to complete the preparation. Specific treatment conditions are as follows: Preheating: Preheat to 380℃ and hold for 10 minutes; Salt bath nitriding treatment: 540℃ for 180 min; Salt bath oxidation treatment: hold at 430℃ for 10 min; Between the salt bath oxidation treatment and the secondary oxidation treatment, a cooling cleaning and surface polishing step was also performed: Cooling and cleaning: The 3D printing mold steel, after salt bath oxidation treatment, is air-cooled at room temperature to make the nitrided layer structure more uniform and dense, while promoting the increase of the diffusion layer depth and effectively decomposing cyanide ions (CN) remaining on the sample surface. - ; Surface polishing: Polishing the surface of the 3D printing mold steel removes any loose layers that may form on the surface, reducing the risk of tensile stress in the oxide film during subsequent secondary oxidation, thereby improving the material's corrosion resistance. Secondary oxidation treatment: hold at 400℃ for 20 minutes; Oiling treatment: Immerse the sample in 30# machine oil.

[0071] The 3D printing mold steel obtained by the above preparation method has excellent comprehensive properties, with a hardness of 54 HRC, a tensile strength of 1950 MPa, a yield strength of 1750 MPa, an elongation at break of 9.5%, and an impact toughness of 17 J / cm. 2 At a high temperature of 650℃, the mold steel still maintains a hardness of 44HRC and good thermal fatigue resistance. Compared with Example 1, this example optimizes the preparation process parameters, especially the gas atomization powder preparation and ultrasonic rolling treatment parameters, resulting in a more uniform surface quality and internal structure of the mold steel, further improving its service life and operational stability.

[0072] Example 3: This embodiment provides a method for preparing 3D printing mold steel. The composition of the 3D printing mold steel, by mass percentage, includes: C: 0.25wt%, Cr: 4.0wt%, Ni: 2.5wt%, Co: 5.0wt%, Mo: 2.5wt%, V: 0.8wt%, Si: 0.8wt%, Nb: 0.7wt%, Al: 1.0wt%, Ti: 0.3wt%, Cu: 0.05wt%, Mn: 0.05wt%, with the balance being Fe and other unavoidable impurities.

[0073] The method for preparing the 3D printing mold steel includes the following steps: S1: Melting: Place the raw materials into a vacuum induction heating furnace and control the vacuum level at 10. -3 Up to 10 -4 The melting temperature was 1600℃, and the melting time was 2.5 hours, forming a homogeneous alloy liquid. During the melting process, the alloy liquid needed to be stirred regularly to ensure that all components were fully and evenly mixed.

[0074] S2: Gas Atomization Powder Production: The molten alloy is atomized using a gas atomization device with high-pressure argon gas at a pressure of 4 MPa and a flow rate of 7 kg / min, resulting in alloy powder with a particle size of 15-53 μm. During the gas atomization process, by controlling the gas pressure and nozzle angle, the powder exhibits good sphericity and flowability, which is beneficial for the uniformity of powder spreading in subsequent 3D printing processes.

[0075] S3: 3D Printing: Using a selective laser melting device to melt alloy powder layer by layer to form a shape. The laser power is 200W, the scanning speed is 800mm / s, and the powder thickness is 30μm; or the laser power is set to 300W, the scanning speed is 1200mm / s, and the powder thickness is 50μm. During the printing process, a cross-scanning strategy is adopted, and the scanning directions of adjacent layers are perpendicular to each other to reduce the accumulation of internal stress and anisotropy.

[0076] S4: Heat treatment: The molded mold steel is tempered at 600℃ for 3 times, with each tempering lasting 3 hours. The cooling method is air cooling to obtain 3D printing mold steel. Multiple tempering treatments can effectively reduce the internal stress of the material and improve its toughness and dimensional stability.

[0077] S5: Post-processing S51: Ultrasonic Roller Burnishing: The tempered 3D printing mold steel is subjected to ultrasonic roller burnishing with an ultrasonic amplitude of 10μm, a static pressure of 1000N, and an ultrasonic frequency of 30kHz. Ultrasonic roller burnishing can effectively improve the surface quality of the material, increase surface hardness and fatigue resistance, while reducing surface microcracks and defects.

[0078] S52: The 3D printing mold steel is sequentially subjected to preheating treatment, salt bath nitriding treatment, salt bath oxidation treatment, secondary oxidation treatment, and oiling treatment to complete the preparation. Specific treatment conditions are as follows: Preheating: Preheat to 380℃ and hold for 30 minutes; Salt bath nitriding treatment: 580℃ for 180 min; Salt bath oxidation treatment: hold at 430℃ for 30 minutes; Cooling and cleaning: The 3D printing mold steel, after salt bath oxidation treatment, is air-cooled at room temperature to make the nitrided layer structure more uniform and dense, while promoting the increase of the diffusion layer depth and effectively decomposing cyanide ions (CN) remaining on the sample surface. - .

[0079] Surface polishing: Polishing the surface of the 3D printing mold steel removes any loose layers that may form on the surface, reducing the risk of tensile stress in the oxide film during subsequent secondary oxidation, thereby improving the material's corrosion resistance.

[0080] Secondary oxidation treatment: The polished mold steel is placed in a secondary oxidation salt bath, the temperature is controlled at 400℃, and it is kept at this temperature for 30 minutes. Secondary oxidation can further improve the density and corrosion resistance of the oxide film.

[0081] Oiling treatment: Immerse the treated mold steel in 50# machine oil to form a protective oil film, prevent damage to the oxide layer, and provide additional lubrication and rust protection.

[0082] The 3D printing mold steel prepared using the above process exhibits excellent comprehensive properties, with a hardness reaching 54 HRC, a bending strength of 1900 MPa, a yield strength of 1760 MPa, an elongation at break of 9.0%, and an impact toughness of 17.2 J / cm². 2 Even at a high temperature of 650℃, this mold steel still maintains a hardness of 43HRC and good thermal fatigue resistance, as well as good corrosion resistance and thermal stability. It is particularly suitable for the rapid manufacturing of complex-shaped molds and mold applications with high performance requirements.

[0083] Example 4: Example 4 provides a method for preparing 3D printing mold steel, which is the same as the method for preparing 3D printing mold steel described in Example 3. The composition of the 3D printing mold steel is: C: 0.2wt%, Cr: 3.5wt%, Ni: 2.2wt%, Co: 4.5wt%, Mo: 2.2wt%, V: 0.6wt%, Si: 0.5wt%, Nb: 0.6wt%, Al: 0.8wt%, Ti: 0.2wt%, Cu: 0.08wt%, Mn: 0.08wt%, with the balance being Fe and other unavoidable impurities.

[0084] The 3D printing mold steel prepared using the above process exhibits excellent comprehensive properties, with a hardness reaching 55 HRC, a tensile strength of 1700 MPa, a yield strength of 1550 MPa, an elongation at break of 10.5% (slightly better plasticity), and an impact toughness of 18.0 J / cm². 2(More focused on toughness), the high-temperature hardness (650℃) is 41HRC. Due to the relatively low levels of reinforcing elements such as carbon, cobalt, molybdenum, and vanadium, the hardness and strength of Example 4 are slightly inferior to those of Example 3, but its plasticity and toughness are better. It is suitable for mold applications with high requirements for forming accuracy and crack resistance, and is especially suitable for the printing and manufacturing of molds with complex shapes or thin walls.

[0085] Example 5: Example 5 provides a method for preparing 3D printing mold steel, which is the same as the method for preparing 3D printing mold steel described in Example 3. The composition of the 3D printing mold steel is: C: 0.3wt%, Cr: 5.0wt%, Ni: 3.0wt%, Co: 6.0wt%, Mo: 3.0wt%, V: 1.0wt%, Si: 1.2wt%, Nb: 1.0wt%, Al: 1.5wt%, Ti: 0.5wt%, Cu: 0.1wt%, Mn: 0.1wt%, with the balance being Fe and other unavoidable impurities.

[0086] The 3D printing mold steel prepared using the above process exhibits excellent comprehensive properties, with a hardness reaching 56–57 HRC, tensile strength of 2000 MPa, yield strength of 1800 MPa, elongation at break of 7.5% (slightly decreased), and impact toughness of 15.5 J / cm². 2 High temperature hardness (650℃): 45 HRC; Example 5 significantly enhances the material's resistance to high temperature softening and hardness by increasing the content of key alloying elements (such as C, Co, Cr, Mo, V, Nb). It is particularly suitable for hot work dies under high load, high impact, and continuous working environments. Its resistance to thermal fatigue and high temperature strength are among the best in the system of this invention, making it suitable for use in extreme working conditions.

[0087] To further explain the technical effects of the present invention, comparative examples are provided below: Comparative Example 1: Comparative Example 1 had the exact same ingredient ratios as Example 3, and also used the same melting, atomization powder preparation, 3D printing, and heat treatment steps. However, the ultrasonic rolling process parameters used a traditional, weaker combination of parameters, as follows: In step S51, the ultrasonic rolling amplitude is 5 μm; The static pressure is 300N; The ultrasonic frequency is 20kHz.

[0088] The other processing steps are the same as in Example 3.

[0089] Experimental results show that: In this comparative example, the ultrasonic rolling strength was insufficient. Although it slightly improved the surface quality, the shallow depth of plastic deformation and insufficient dislocation density during rolling prevented sufficient induction of surface recrystallization and strengthening phase precipitation. Combined with the Nb, Ti, and V alloy system used, the potential of these elements to construct nano-precipitates was not effectively utilized, resulting in limited strengthening effect. Its specific properties include: hardness of 48 HRC, relatively fast fatigue crack propagation rate, approximately 20% decrease in thermal fatigue life, and impact toughness of 15.3 J / cm². 2 Slightly lower than 17.2 J / cm in Example 3. 2 In the microstructure, the surface strengthening layer is insufficient in thickness and the stress relief is inadequate. Comparative Example 1 demonstrates that ultrasonic rolling with only weak parameters cannot work synergistically with high Nb / V / Ti alloy systems, and cannot achieve synergistic precipitation of surface recrystallization strengthening and strengthening phases. Example 3 of this invention, through parameter optimization, enables ultrasonic rolling to achieve a synergistic mechanism of "strengthening + toughness coordinated development" with a specific alloy system, significantly improving overall mechanical and fatigue properties.

[0090] Comparative Example 2: Comparative Example 2 is identical to Example 3 in alloy composition and front-end preparation processes (including smelting, powder preparation, 3D printing, heat treatment, and ultrasonic rolling), but adopts a traditional simplified scheme in the post-processing: The post-processing sequence was: salt bath nitriding → primary oxidation → oiling treatment. Cooling cleaning, surface polishing and secondary oxidation were not included. Other parameters were the same as in Example 3.

[0091] In this comparative example, although a certain nitrided layer and oxide film can be formed on the surface, the residual cyanide after nitriding is not completely decomposed due to the lack of cooling, cleaning and polishing, and the oxide film has poor adhesion due to the presence of a loose layer; at the same time, the lack of a secondary oxidation process results in insufficient film density and insufficient release of tensile stress.

[0092] During the testing of the sample prepared in Comparative Example 2, its surface corrosion rate was more than 35% higher than that in Example 3; and after 30 high-temperature thermal cycles, obvious film peeling occurred on the surface; the hardness at high temperature (650℃) was 39HRC, lower than the 43HRC of Example 3; microcracks were visible in the oxide layer in the metallographic structure, affecting the thermal fatigue life; Comparative Example 2 demonstrated that the traditional post-treatment process cannot fully stimulate the potential of elements such as Cr and V to build a stable oxide film on the surface, resulting in a film that is easy to peel off and has poor corrosion resistance and thermal stability. In contrast, Example 3 of this invention, by introducing processes such as cooling cleaning, polishing, and secondary oxidation, enhanced the density and stability of the surface structure, demonstrating a good synergy between the treatment process and the composition system, and significantly improving the heat resistance and corrosion resistance of the mold steel.

[0093] To compare the effects of different surface treatment processes on the wear resistance of the 3D printed mold steel of this invention, this invention further uses three samples in different states for comparative testing. Sample 1 is the matrix material prepared according to steps S1–S4 of Example 2 of this invention, which only underwent conventional surface polishing without any surface strengthening processes such as ultrasonic rolling or salt bath nitriding, and serves as a baseline control group. Sample 2 is from Example 2, which, after completing steps S1–S4, did not undergo ultrasonic rolling but directly underwent salt bath nitriding and oxidation treatment as defined in step S52, thereby obtaining a surface structure strengthened by a single chemical heat treatment. Sample 3 is from Example 2 of this invention, which, after completing steps S1–S4, first underwent ultrasonic rolling surface plastic strengthening according to step S51, and then underwent preheating, salt bath nitriding, and oxidation treatments according to step S52, thereby forming a composite integrated strengthening layer structure with the synergistic effect of USRP and nitriding.

[0094] The wear test parameters include: the wear test is carried out at 300℃, using reciprocating friction, with a load of 50 N, a stroke of 10 mm, a frequency of 3 Hz, a test time of 30 min, and the wear pair is Si3N4 ceramic balls (10 mm in diameter).

[0095] The test results are as follows: Wear volume

[0096] Based on the above tests, the wear volume of sample 1 (the original sample without wear) was 0.052 mm. 3 The wear mass was 0.0074 g; the wear volume of sample 2 decreased to 0.047 mm. 3 The wear mass was significantly reduced to 0.0009 g; the wear of sample No. 3, which underwent USRP + nitriding composite treatment, was the lowest, with a wear volume of only 0.042 mm. 3 The wear mass was 0.0006 g, indicating that the composite surface strengthening process can significantly improve the wear resistance of the material.

[0097] As shown in Figures 1-3, there are significant differences in the three-dimensional wear morphology of samples 1, 2, and 3: Sample 1 has the most obvious wear grooves with a large depth and a high amount of surface material removed; Sample 2, after salt bath nitriding treatment, has a reduced wear groove depth and a relatively gentle groove profile; while Sample 3, under the combined action of ultrasonic rolling and salt bath nitriding, has the shallowest wear grooves, a relatively smooth surface, and a significantly reduced degree of wear. The two-dimensional wear morphology shown in Figure 4-6 further verifies the above results: Among them, the wear area of ​​sample 1 exhibits a deep groove-like feature, with clear wear mark boundaries and obvious differences in depth; the wear mark depth of sample 2 is smaller than that of sample 1, and the surface height change tends to be gentle; the wear mark of sample 3 is the shallowest, and the wear area transitions smoothly, indicating that the composite strengthening treatment significantly inhibits the formation of wear grooves. As shown in the friction coefficient curves in Figure 7, sample 1 has the highest friction coefficient with a large fluctuation range; sample 2 has a lower friction coefficient, but still exhibits some fluctuation; sample 3 has the lowest friction coefficient with the most stable change, indicating that the surface after composite treatment has better anti-friction ability and more stable friction behavior. The wear track profile depth curves shown in Figure 8 further characterize the wear differences of different samples. Sample 1 has the deepest wear track with a clear valley bottom; sample 2 has a reduced wear track depth; sample 3 has the shallowest wear track, and the wear track width is also reduced. It can be seen that the present invention, through the composite treatment of ultrasonic rolling and salt bath nitriding, can significantly reduce the depth and width of wear grooves, making the material surface exhibit better wear resistance.

[0098] The analysis of the above embodiments and comparative examples further demonstrates the significant technical effects brought about by the high synergy between the composition design and the preparation process of this invention. This invention not only rationally selects strengthening elements such as C, Cr, Ni, Co, Mo, V, Nb, and Ti in the alloy system and precisely controls their content to ensure that the Ms point is stable within the ideal martensitic transformation temperature range (280–330℃), but also fully explores and stimulates the potential of the strengthening phase in the alloy and the structural control ability of the surface microstructure through the process optimization of ultrasonic rolling and post-treatment rhythm in the preparation process. In particular, in Example 3, the ultrasonic rolling parameters and the high Nb / V / Ti alloy system work together to achieve a composite mechanism of "plastic-induced recrystallization + nanoprecipitation strengthening", which significantly improves the surface strengthening depth, fatigue resistance and impact toughness. At the same time, the cooling cleaning, polishing and secondary oxidation steps in the post-treatment process are adapted to the composition distribution of the Cr / V rich surface, control the stress gradient of the oxide film, and effectively improve the film density, adhesion and corrosion resistance. Comparative Examples 1 and 2 clearly demonstrate that when the ultrasonic rolling or post-processing process fails to match the alloy system, even if the alloy composition remains unchanged, its final performance will significantly decrease. This verifies that the synergistic optimization strategy between "process-composition-structure-performance" in this invention is an irreplaceable technological innovation.

[0099] In summary, this invention significantly improves the mechanical properties, thermal stability, and service reliability of 3D printing mold steel through the synergistic integration of chemical composition design, process parameter control, and post-processing steps. It solves problems such as molding cracking, difficulty in achieving both strength and toughness, and film layer peeling in existing technologies. It has good prospects for industrial application and promotion value, and possesses significant innovation, practicality, and feasibility.

[0100] In the description of this application, the references to terms such as "an embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0101] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A 3D printing mold steel, characterized in that, The 3D printing mold steel comprises, by weight ratio: C: 0.2-0.4wt%, Cr: 2-7wt%, Ni: 1.5-5.0wt%, Co: 3.0-7.0wt%, Mo: 0-3.0wt%, V: 0-1.0wt%, Si: 0-1.0wt%, Nb: 0-1.0wt%, Al: 0-2wt%, Ti: 0-1.0wt%, Cu: 0-1.0wt%, Mn: 0-1.0wt%, with the balance being Fe and other unavoidable impurities. The martensitic transformation temperature Ms of the 3D printing mold steel is controlled between 280-330℃.

2. The 3D printing mold steel according to claim 1, characterized in that, By weight ratio, the 3D printing mold steel comprises: C: 0.2-0.3wt%, Cr: 3.0-5.0wt%, Ni: 2.0-3.0wt%, Co: 4.0-6.0wt%, Mo: 2.0-3.0wt%, V: 0.5-1.0wt%, Si: 0.3-1.2wt%, Nb: 0.5-1.0wt%, Al: 0-1.5wt%, Ti: 0-0.5wt%, Cu: 0-0.1wt%, Mn: 0-0.1wt%, with the balance being Fe and other unavoidable impurities.

3. A method for preparing the 3D printing mold steel according to any one of claims 1-2, characterized in that, Includes the following steps: S1: Melting: Place the raw materials into a vacuum induction heating furnace and control the vacuum level at 10. -3 Up to 10 -4 Between Pa, the melting temperature is 1550-1650℃, and the melting time is 2-3 hours to form a uniform alloy liquid; S2: Gas atomization powder making: The alloy liquid is made into powder by passing it through a gas atomization device to obtain alloy powder with a particle size of 15-53μm; S3: 3D printing: using a selective laser melting device to melt the alloy powder layer by layer to form a shape; S4: Heat treatment: Temper the mold steel after forming at a temperature of 400-650℃ and cool it by air cooling or furnace cooling to obtain 3D printing mold steel.

4. The method for preparing 3D printing mold steel according to claim 3, characterized in that, In step S2, the conditions for powder production by the gas atomization device are as follows: high-pressure argon is used as the atomizing gas, and the argon pressure is 3-5 MPa, and the flow rate of the alloy liquid is 5-10 kg / min.

5. The method for preparing 3D printing mold steel according to claim 3, characterized in that, In step S3, the printing parameters for the layer-by-layer melting and forming are: laser power 200-300W, scanning speed 800-1200mm / s, and powder thickness 30-50μm.

6. The method for preparing 3D printing mold steel according to claim 3, characterized in that, In step S4, the tempering process is performed in 2-3 cycles, with each tempering cycle lasting 2-3 hours.

7. The method for preparing 3D printing mold steel according to claim 3, characterized in that, After step S4 is completed, the following steps are also included: S5: Post-processing S51: Ultrasonic rolling treatment is performed on tempered 3D printing mold steel. S52: The 3D printing mold steel is subjected to preheating treatment, salt bath nitriding treatment, salt bath oxidation treatment, secondary oxidation treatment and oiling treatment in sequence to complete the preparation.

8. The method for preparing 3D printing mold steel according to claim 7, characterized in that, In step S51, the processing parameters for ultrasonic rolling include: ultrasonic amplitude of 5-10 μm, static pressure of 600-1000 N, and ultrasonic frequency of 30 kHz.

9. The method for preparing 3D printing mold steel according to claim 7, characterized in that, In step S52, the conditions for the preheating treatment, salt bath nitriding treatment, salt bath oxidation treatment, secondary oxidation treatment, and oiling treatment include: preheating to 250~380℃ and holding for 10~30 min; salt bath nitriding treatment: holding at 520-580℃ for 10-180 min; salt bath oxidation treatment: holding at 360-430℃ for 10-30 min; secondary oxidation treatment: holding at 400℃ for 10-30 min; and oiling treatment: immersing the sample in 20-40# machine oil.

10. The method for preparing 3D printing mold steel according to claim 9, characterized in that, In step S52, the process between the salt bath oxidation treatment and the secondary oxidation treatment further includes a cooling cleaning and surface polishing step, including: Cooling and cleaning: The 3D printing mold steel, after salt bath oxidation treatment, is air-cooled at room temperature to make the nitrided layer structure more uniform and dense, while promoting the increase of the diffusion layer depth and effectively decomposing cyanide ions (CN) remaining on the sample surface. - ; Surface polishing: Polishing the surface of the 3D printing mold steel removes any loose layers that may form on the surface, reducing the risk of tensile stress in the oxide film during subsequent secondary oxidation, thereby improving the material's corrosion resistance.

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