Die steel material for additive manufacturing lattice die and preparation process of die steel material

Abstract

The invention discloses a die steel material for additive manufacturing of a lattice die and a preparation process of the die steel material, and the preparation process comprises the following steps: heating and melting an alloy base material, atomizing and pulverizing to obtain alloy base material powder, mixing mixed additive phase powder formed by mixing nano zirconium nitride particles and AlTiLa intermediate alloy powder with the alloy base material powder, and carrying out heat treatment to obtain the die steel material for additive manufacturing of the lattice die. And the die steel powder is subjected to selective laser melting treatment and heat treatment, and then the die steel material is obtained. Under the laser high temperature of selective laser melting treatment, interface reaction of zirconium nitride, AlTiLa intermediate alloy and alloy base material powder can be triggered, formation of intermetallic compounds, refining of carbide particles, purification of grain boundaries and improvement of the heat conduction capacity of the die steel material are promoted, and after heat treatment, residual stress can be fully released, so that the service life of the die steel material is prolonged. Internal stress and structure defects are eliminated, anisotropy is effectively eliminated, and the thermal fatigue resistance of the die steel material is prolonged.

Description

Technical Field

[0001] This invention relates to the field of mold steel technology, and more specifically, to a mold steel material for additive manufacturing lattice molds and its preparation process. Background Technology

[0002] Additive manufacturing is a digital manufacturing technology that creates solid parts by layer-by-layer material deposition based on 3D model data. It enables near-net-shape forming of complex structural components and is widely used in aerospace, automotive, and medical fields. Due to their lightweight and multifunctional design characteristics, lattice structures are highly compatible with additive manufacturing technology, allowing for the integrated molding process to solve problems such as irregular cavities and embedded flow channels that are difficult to process using traditional molds. For example, it can be used in the medical industry for customized prosthetic molds, or in the daily necessities industry for the rapid production of personalized packaging molds, making it particularly suitable for flexible manufacturing needs involving small batches and diverse product varieties.

[0003] Martensitic aging steels (such as 18Ni300) have attracted much attention in the field of additive manufacturing due to their high strength, high toughness, and easy age hardening properties, especially suitable for the manufacture of complex lightweight structures (such as lattice molds). However, most martensitic aging steels have limited thermal conductivity. In structures like lattice molds with extremely uneven heat dissipation, this can easily exacerbate the uneven distribution of residual stress, increasing the risk of deformation and cracking. Furthermore, for lattice molds with interconnected and repeating three-dimensional structures composed of rods and nodes, the layer-by-layer deposition in additive manufacturing can easily lead to anisotropic mechanical properties. During thermal fatigue, the surface of the mold steel material undergoes repeated heating and cooling cycles, generating thermal stress. Uneven distribution of thermal stress in different directions can easily lead to local stress concentration, becoming a path for crack initiation and propagation, thereby reducing the thermal fatigue resistance of the mold steel material. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a mold steel material for additive manufacturing lattice molds and its preparation process.

[0005] A process for preparing a mold steel material for additive manufacturing lattice molds includes the following steps: S1: The alloy substrate is heated and melted, and then atomized into powder under inert gas conditions. After sieving and drying, the alloy substrate powder is obtained. S2: Mix nano-zirconium nitride particles with AlTiLa master alloy powder at a mass ratio of (0.8~1.2):1 to obtain mixed additive phase powder. Ball mill the alloy substrate powder and the mixed additive phase powder together. The amount of mixed additive phase powder added is 2.2~4% of the mass of the alloy substrate powder to obtain mold steel powder. S3: Selective laser melting is performed on the mold steel powder to obtain a mold steel processing sample after selective laser melting treatment; S4: Heat-treat the mold steel sample to obtain the mold steel material; The specific steps of heat treatment are as follows: Annealing: heat to 820–950℃, hold for 4–8 hours, then air cool to 560–600℃; Solution treatment, heating to 980–1010℃, holding at that temperature for 1–2 hours, and then oil cooling to room temperature; For aging, heat to 430-460℃, hold for 2-6 hours, and then air cool to room temperature.

[0006] Furthermore, the alloy substrate is composed of the following elements by mass percentage: C: 0.01–0.03%, Cr: 0.2–1.1%, Mo: 4.6–5.4%, Ni: 16.5–20.0%, Co: 7.5–9.5%, Al: 0.04–0.12%, with the balance being Fe and unavoidable impurities; The alloy substrate powder is a spherical powder with a particle size of 15–53 μm.

[0007] Furthermore, the atomizing pressure of the gas atomization powder is 3-6 MPa, and the airflow velocity is 120-180 m / s.

[0008] Furthermore, the particle size of the nano-zirconium nitride particles is 50–100 nm.

[0009] Furthermore, the particle size of the AlTiLa master alloy powder is 3-10 μm. The AlTiLa master alloy powder is obtained by heating and melting the AlTiLa master alloy and then atomizing it into powder. The mass fraction of Ti in the AlTiLa master alloy is 5%, and the mass fraction of La is 3%.

[0010] Furthermore, the parameters for selective laser melting (SLM) are as follows: powder layer thickness 40–80 µm, laser scanning power 120–500 W, scanning speed 400–1000 mm / s, scanning spacing 50–1000 µm, and laser energy density 50–160 J / mm². 3 The substrate preheating temperature is 180-300℃.

[0011] Furthermore, the annealing heating rate is 8–10 °C / min.

[0012] Furthermore, the heating rate for solid solution is 10–15 °C / min.

[0013] Furthermore, the aging heating rate is 5–10 °C / min.

[0014] A mold steel material for additive manufacturing lattice molds is prepared by the aforementioned preparation process of a mold steel material for additive manufacturing lattice molds.

[0015] Compared with the prior art, the present invention has at least the following advantages: 1. In this invention, nano-zirconium nitride particles and AlTiLa master alloy powder are ball-milled and mixed, then added to alloy substrate powder to prepare mold steel powder. The nano-zirconium nitride particles and AlTiLa master alloy powder, as additive phases, can provide high thermal conductivity, interface strengthening, and grain refinement, thereby improving the strength and toughness of the mold steel material. Under the high temperature of selective laser melting, the interface reaction between zirconium nitride, AlTiLa master alloy, and alloy substrate powder is triggered, promoting the combination of some zirconium nitride and AlTiLa master alloy with elements such as iron and nickel in the alloy substrate powder to form intermetallic compounds, refining carbide particles and purifying grain boundaries. At the same time, the nano-zirconium nitride particles and AlTiLa master alloy powder can react with each other, which is conducive to the combination of titanium in AlTiLa master alloy with nitrogen elements released from some zirconium nitride to form titanium nitride. This allows titanium nitride and zirconium nitride to synergistically form composite nitrides, constituting a double-dispersion strengthening network, further improving the mechanical properties and thermal conductivity of the mold steel material.

[0016] 2. In this invention, the amount of mixed additive phase powder is controlled within the range of 2.2% to 4% of the alloy base powder mass. This is beneficial to achieving a balance between grain refinement, inclusion control, and process adaptability, ensuring the additive manufacturing performance of the mold steel powder. It not only guarantees the mechanical properties of the mold steel material but also ensures that the mold steel material has high thermal conductivity, avoiding problems such as insufficient grain refinement, increased brittleness, and insignificant performance improvement that affect the mechanical and thermal properties of the mold steel material.

[0017] 3. Conventional heat treatment of martensitic aging steel typically involves only solution treatment and aging. Compared to conventional heat treatment of martensitic aging steel, this invention performs a high-temperature annealing step before solution treatment. High-temperature annealing helps to fully release residual stress, eliminate internal stress and structural defects generated during selective laser melting, and make the microstructure of the mold steel material more uniform and refined, reducing the risk of deformation and cracking. Furthermore, solution treatment allows alloying elements to fully dissolve into the solid solution, forming a low-carbon lath martensitic matrix. Aging treatment then promotes precipitation strengthening of the matrix, facilitating the uniform precipitation of strengthening phases and effectively pinning dislocations within the low-carbon lath martensitic matrix. This effectively eliminates anisotropy and improves the thermal fatigue resistance of the mold steel material. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: A process for preparing mold steel material for additive manufacturing lattice molds, specifically including the following steps: S1: The alloy substrate is heated and melted under vacuum conditions, and then atomized into powder under argon conditions. The atomizing pressure of the gas is 4.5MPa and the gas flow rate is 150m / s. Subsequently, after sieving and drying, spherical powdered alloy substrate powder with a particle size range of 15-53μm is obtained. The alloy substrate is composed of the following elements by mass percentage: C: 0.02%, Cr: 0.6%, Mo: 5.0%, Ni: 18.0%, Co: 8.0%, Al: 0.08%, with the balance being Fe and unavoidable impurities; S2: 75nm nano-zirconium nitride particles and AlTiLa master alloy powder with a particle size range of 3-10μm are added to a V-type powder mixer at a mass ratio of 1:1 and mixed for 21 hours to obtain mixed additive phase powder. Then, the alloy base powder and the mixed additive phase powder are ball-milled and mixed. The amount of mixed additive phase powder added is 3.1% of the mass of the alloy base powder to obtain mold steel powder. The AlTiLa master alloy powder is obtained by heating, melting and atomizing AlTiLa master alloy. The mass fraction of Ti in AlTiLa master alloy is 5% and the mass fraction of La is 3%. S3: Selective laser melting of mold steel powder. The parameters for selective laser melting are: powder layer thickness of 60µm, laser scanning power of 310W, scanning speed of 700mm / s, scanning spacing of 500µm, and laser energy density of 100J / mm². 3 The substrate is preheated to 240℃, and after selective laser melting, a mold steel sample is obtained. S4: Heat-treat the mold steel sample to obtain the mold steel material; Heat treatment includes annealing, solution treatment, and aging. Annealing: Heat to 885℃ at a rate of 9℃ / min, hold for 6 hours, and air cool to 580℃. Solution treatment, heating to 995℃ at a rate of 12.5℃ / min, holding for 1.5h, and then oil cooling to room temperature; Aging time: Heat to 445℃ at a rate of 7.5℃ / min, hold for 4 hours, and then air cool to room temperature.

[0020] Example 2: A process for preparing mold steel material for additive manufacturing lattice molds, specifically including the following steps: S1: The alloy substrate is heated and melted under vacuum conditions, and then atomized into powder under argon conditions. The atomizing pressure of the gas is 6MPa and the gas flow rate is 180m / s. Subsequently, after sieving and drying, spherical powdered alloy substrate powder with a particle size range of 15-53μm is obtained. The alloy substrate is composed of the following elements by mass percentage: C: 0.03%, Cr: 1.1%, Mo: 5.4%, Ni: 20.0%, Co: 9.5%, Al: 0.12%, with the balance being Fe and unavoidable impurities; S2: 100 nm nano-zirconium nitride particles and AlTiLa master alloy powder with a particle size range of 3-10 μm are added to a V-type powder mixer at a mass ratio of 1.2:1 and mixed for 24 h to obtain mixed additive phase powder. Then, the alloy base powder and the mixed additive phase powder are ball-milled and mixed. The amount of mixed additive phase powder added is 4% of the mass of the alloy base powder to obtain mold steel powder. The AlTiLa master alloy powder is obtained by heating, melting and atomizing AlTiLa master alloy. The mass fraction of Ti in AlTiLa master alloy is 5% and the mass fraction of La is 3%. S3: Selective laser melting of mold steel powder. The parameters for selective laser melting are: powder layer thickness of 80µm, laser scanning power of 500W, scanning speed of 1000mm / s, scanning spacing of 1000µm, and laser energy density of 160J / mm². 3 The substrate is preheated to 300℃, and after selective laser melting, a sample of mold steel is obtained. S4: Heat-treat the mold steel sample to obtain the mold steel material; Heat treatment includes annealing, solution treatment, and aging. Annealing: heat to 950℃ at a rate of 10℃ / min, hold for 8 hours, and air cool to 600℃. Solution treatment, heating to 1010℃ at a rate of 15℃ / min, holding for 2 hours, and then oil cooling to room temperature; Aging time: Heat to 460℃ at a rate of 10℃ / min, hold for 6 hours, and then air cool to room temperature.

[0021] Example 3: A process for preparing mold steel material for additive manufacturing lattice molds, specifically including the following steps: S1: The alloy substrate is heated and melted under vacuum conditions, and then atomized into powder under argon conditions. The atomization pressure of the gas is 3MPa and the gas flow rate is 120m / s. Subsequently, after sieving and drying, spherical powdered alloy substrate powder with a particle size range of 15-53μm is obtained. The alloy substrate is composed of the following elements by mass percentage: C: 0.01%, Cr: 0.2%, Mo: 4.6%, Ni: 16.5%, Co: 7.5%, Al: 0.04%, with the balance being Fe and unavoidable impurities; S2: Nano-zirconium nitride particles with a particle size of 50 nm and AlTiLa master alloy powder with a particle size range of 3-10 μm are added to a V-type powder mixer at a mass ratio of 0.8:1 and mixed for 18 hours to obtain mixed additive phase powder. Then, the alloy base powder and the mixed additive phase powder are ball-milled and mixed. The amount of mixed additive phase powder added is 2.2% of the mass of the alloy base powder to obtain mold steel powder. The AlTiLa master alloy powder is obtained by heating, melting and atomizing AlTiLa master alloy. The mass fraction of Ti in AlTiLa master alloy is 5% and the mass fraction of La is 3%. S3: Selective laser melting of mold steel powder. The parameters for selective laser melting are: powder layer thickness of 40µm, laser scanning power of 120W, scanning speed of 400mm / s, scanning spacing of 50µm, and laser energy density of 50J / mm². 3 The substrate is preheated to 180℃, and after selective laser melting, a sample of mold steel is obtained. S4: Heat-treat the mold steel sample to obtain the mold steel material; Heat treatment includes annealing, solution treatment, and aging. Annealing: heat to 820℃ at a rate of 8℃ / min, hold for 4 hours, and air cool to 560℃. Solution treatment, heating to 980℃ at a rate of 10℃ / min, holding for 1 hour, and then oil cooling to room temperature; Aging time: Heat to 430℃ at a rate of 5℃ / min, hold for 2 hours, and then air cool to room temperature.

[0022] Comparative Example 1 Compared with Example 1, the difference of Comparative Example 1 is that the step of mixing nano-zirconium nitride particles with AlTiLa master alloy powder to prepare mixed additive phase powder in step S2 is removed. Instead, the alloy substrate powder is directly ball-milled and mixed with AlTiLa master alloy powder. The amount of AlTiLa master alloy powder added is 3.1% of the mass of the alloy substrate powder to obtain mold steel powder. The remaining steps remain unchanged to prepare mold steel material, which is referred to as Comparative Example 1.

[0023] Comparative Example 2 Compared with Example 1, the difference of Comparative Example 2 is that the step of mixing nano-zirconium nitride particles with AlTiLa intermediate alloy powder to prepare mixed additive phase powder in step S2 is removed. Instead, the alloy substrate powder is directly ball-milled and mixed with nano-zirconium nitride particles. The amount of nano-zirconium nitride particles added is 3.1% of the mass of the alloy substrate powder to obtain mold steel powder. The remaining steps remain unchanged to prepare mold steel material, which is referred to as Comparative Example 2.

[0024] Comparative Example 3 Compared with Example 1, the difference of Comparative Example 3 is that step S2 is removed, and the mold steel powder in step S3 is replaced with the alloy substrate powder in step S1. The remaining steps remain unchanged, and the mold steel material is prepared. This is referred to as Comparative Example 3.

[0025] Comparative Example 4 Compared with Example 1, the difference of Comparative Example 4 is that the amount of mixed additive phase powder added in step S2 is 2.0% of the mass of alloy base material powder, and the other steps remain unchanged. Mold steel material is prepared and is referred to as Comparative Example 4.

[0026] Comparative Example 5 Compared with Example 1, the difference of Comparative Example 5 is that the amount of mixed additive phase powder added in step S2 is 1.8% of the mass of alloy base powder, and the other steps remain unchanged. Mold steel material is prepared and is referred to as Comparative Example 5.

[0027] Comparative Example 6 Compared with Example 1, the difference of Comparative Example 6 is that the amount of mixed additive phase powder added in step S2 is 4.2% of the mass of alloy base powder, and the other steps remain unchanged. Mold steel material is prepared and is referred to as Comparative Example 6.

[0028] Comparative Example 7 Compared with Example 1, the difference of Comparative Example 7 is that the amount of mixed additive phase powder added in step S2 is 4.4% of the mass of alloy base material powder, and the other steps remain unchanged. Mold steel material is prepared and is referred to as Comparative Example 7.

[0029] According to GB / T22588-2008, the thermal conductivity of the mold steel materials prepared in Examples 1-3 and Comparative Examples 1-7 at room temperature was tested; according to GB / T228.1-2021, the mechanical properties of the mold steel materials prepared in Examples 1-3 and Comparative Examples 1-6 were tested, and the test results are shown in Table 1.

[0030] Table 1: Group Thermal conductivity (W / m·K) Hardness (HRC) Tensile strength (MPa) Elongation at break (%) Example 1 35.64 58 1973 15.7 Example 2 34.88 57 1958 15.2 Example 3 34.25 57 1941 15.5 Comparative Example 1 26.16 50 1662 12.7 Comparative Example 2 24.72 52 1740 13.4 Comparative Example 3 20.25 48 1346 10.4 Comparative Example 4 31.07 52 1862 14.3 Comparative Example 5 30.85 51 1845 13.7 Comparative Example 6 32.26 53 1856 14.6 Comparative Example 7 32.03 51 1851 14.0 As shown in Table 1, the mold steel materials prepared in Examples 1-3 exhibit superior thermal conductivity, hardness, tensile strength, and elongation at break compared to those prepared in Comparative Examples 1-7. A comparison of the test results from Examples 1-3 and Comparative Examples 1-3 reveals that, compared to adding only nano-zirconium nitride particles or AlTiLa master alloy powder, or not adding the mixed additive phase powder, the mold steel material prepared by mixing nano-zirconium nitride particles and AlTiLa master alloy powder, adding the resulting mixed additive phase powder to the alloy substrate powder, and then selectively laser melting exhibits higher thermal conductivity and mechanical properties. The nano-zirconium nitride particles or AlTiLa master alloy powder in the mixed additive phase powder synergistically enhance both thermal conductivity and mechanical properties. A comparison of the test results of Examples 1-3 and Comparative Examples 4-7 shows that when the amount of mixed additive phase powder added is >4% or <2.2%, the thermal conductivity and mechanical properties of the prepared mold steel material will be affected to a certain extent. When the amount of mixed additive phase powder added is <2.2% of the mass of alloy base powder, the improvement in thermal conductivity is limited, the grain refinement strengthening effect is limited, and the improvement in strength and toughness is insufficient. When the amount of mixed additive phase powder added is >4% of the mass of alloy base powder, the hardness, tensile strength and elongation at break of the mold steel material all decrease, and the brittleness of the mold steel material increases.

[0031] Comparative Example 8 Compared with Example 1, Comparative Example 8 differs in that the annealing step in step S4 is removed, and the heat treatment only includes solution treatment and aging, while the other steps remain unchanged, to prepare mold steel material, which is referred to as Comparative Example 8.

[0032] The mold steel materials prepared in Examples 1-3 and Comparative Example 8 were subjected to thermal fatigue resistance tests. The test specimens were 30mm×20mm×5mm in size, and there were 5 test specimens in each group. The test specimens were placed in a heating device and heated to 650℃ for 60s, and then immersed in a water bath at 25℃ for 5s to cool, completing one heating and cooling cycle. The above test steps were repeated until the 2000th heating and cooling cycle was completed. The main crack length of each group of test specimens was recorded after the 1000th and 2000th heating and cooling cycles. The average main crack length of each group of test specimens after the 1000th and 2000th cycles was calculated as the test results. The results are shown in Table 2.

[0033] Table 2: Group Length of the 1000th main crack (μm) Length of the 2000th main crack (μm) Example 1 25.6 84.7 Example 2 28.4 89.4 Example 3 30.7 92.1 Comparative Example 8 57.3 130.7 As shown in Table 2, the mold steel materials prepared in Examples 1-3, after 1000 heating and cooling cycles, had a main crack length of ≤30.7μm on the surface, which was much smaller than the 57.3μm of the mold steel material in Comparative Example 8. After 2000 heating and cooling cycles, the main crack length of the mold steel materials prepared in Examples 1-3 was also smaller than the main crack length of the mold steel material in Comparative Example 8. This indicates that in the heat treatment process of the present invention, a high-temperature annealing step is performed before solution treatment, followed by solution treatment and aging treatment in sequence, which can yield mold steel materials with better thermal fatigue resistance.

[0034] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A process for preparing mold steel material for additive manufacturing lattice molds, characterized in that, Includes the following steps: S1: The alloy substrate is heated and melted, and then atomized into powder under inert gas conditions. After sieving and drying, the alloy substrate powder is obtained. S2: Mix nano-zirconium nitride particles with AlTiLa master alloy powder at a mass ratio of (0.8~1.2):1 to obtain mixed additive phase powder. Ball mill the alloy substrate powder and the mixed additive phase powder together. The amount of mixed additive phase powder added is 2.2~4% of the mass of the alloy substrate powder to obtain mold steel powder. S3: Selective laser melting is performed on the mold steel powder to obtain a mold steel processing sample after selective laser melting treatment; S4: Heat-treat the mold steel sample to obtain the mold steel material; The specific steps of heat treatment are as follows: Annealing: heat to 820–950℃, hold for 4–8 hours, then air cool to 560–600℃; Solution treatment, heating to 980–1010℃, holding at that temperature for 1–2 hours, and then oil cooling to room temperature; For aging, heat to 430-460℃, hold for 2-6 hours, and then air cool to room temperature.

2. The preparation process of a mold steel material for additive manufacturing lattice molds according to claim 1, characterized in that, The alloy base material is composed of the following elements by mass percentage: C: 0.01-0.03%, Cr: 0.2-1.1%, Mo: 4.6-5.4%, Ni: 16.5-20.0%, Co: 7.5-9.5%, Al: 0.04-0.12%, with the balance being Fe and unavoidable impurities; The alloy substrate powder is a spherical powder with a particle size of 15–53 μm.

3. The preparation process of a mold steel material for additive manufacturing lattice molds according to claim 2, characterized in that, The atomizing pressure of the gas atomization powder is 3-6 MPa, and the airflow velocity is 120-180 m / s.

4. The preparation process of a mold steel material for additive manufacturing lattice molds according to claim 3, characterized in that, The particle size of the nano-zirconium nitride particles is 50–100 nm.

5. The preparation process of a mold steel material for additive manufacturing lattice molds according to claim 4, characterized in that, The particle size of AlTiLa master alloy powder is 3-10 μm. AlTiLa master alloy powder is obtained by heating, melting and atomizing AlTiLa master alloy. The mass fraction of Ti in AlTiLa master alloy is 5% and the mass fraction of La is 3%.

6. The preparation process of a mold steel material for additive manufacturing lattice molds according to claim 5, characterized in that, The parameters for selective laser melting (SLM) are as follows: powder layer thickness 40–80 µm, laser scanning power 120–500 W, scanning speed 400–1000 mm / s, scanning spacing 50–1000 µm, and laser energy density 50–160 J / mm². 3 The substrate preheating temperature is 180-300℃.

7. The preparation process of a mold steel material for additive manufacturing lattice molds according to claim 6, characterized in that, The annealing heating rate is 8–10 °C / min.

8. The preparation process of a mold steel material for additive manufacturing lattice molds according to claim 7, characterized in that, The heating rate for solid solution is 10–15 °C / min.

9. The preparation process of a mold steel material for additive manufacturing lattice molds according to claim 8, characterized in that, The aging heating rate is 5–10 °C / min.

10. A mold steel material for additive manufacturing lattice molds, characterized in that, It is prepared by the preparation process of a mold steel material for additive manufacturing lattice molds according to any one of claims 1-9.