High-thermal-conductivity high-hardness plastic mold die steel and preparation method thereof

Abstract

The application discloses a high-thermal-conductivity and high-hardness plastic mold steel and a preparation method thereof. In view of the low thermal conductivity, insufficient hardness and poor wear resistance of the existing plastic mold steel, the application realizes the optimization of the comprehensive performance of the material by directional modification of nano silicon nitride, titanium alloy powder and graphene, in combination with a specific component proportion and a preparation process. The mold steel is composed of a 42CrMo steel base body, modified nano silicon nitride, modified titanium alloy powder, modified graphene and alloy elements such as vanadium iron and niobium iron. The preparation process comprises the steps of batching, mixing, vacuum induction smelting, forging, heat treatment and finishing. Through the synergistic effect of the modified material and the alloy elements, the hardness of the mold steel reaches 62-65HRC, the thermal conductivity is 48-55W / (mK), the tensile strength is 1250-1300MPa, the impact toughness is 25-28J / cm 2 , and the wear loss is 6.8-8.5mg, the interface compatibility of the reinforced phase and the base body is improved, and the balance among the thermal conductivity, the hardness, the toughness and the wear resistance is realized.

Description

Technical Field

[0001] This invention relates to the field of mold steel technology, and in particular to a high thermal conductivity and high hardness plastic mold steel and its preparation method. Background Technology

[0002] Plastic mold steel is a core material in the injection molding process, and its performance directly determines the molding accuracy, production efficiency, and mold life of the injection molded parts. Currently, commonly used plastic mold steels (such as 42CrMo and S136) have two major drawbacks: firstly, their thermal conductivity is low (typically only 25-35 W / (m²)). K)) During the injection molding process, the heat transfer of the mold is slow, resulting in uneven cooling of the injection molded parts, which can easily cause defects such as warping and shrinkage marks, and prolong the molding cycle; secondly, the hardness and wear resistance are insufficient (the hardness after conventional heat treatment is about 50-55HRC), which makes it easy to wear and scratch under long-term high pressure and high speed friction conditions, leading to mold failure.

[0003] To improve the aforementioned properties, existing technologies often employ the addition of ceramic particles (such as silicon nitride and alumina) or alloying elements (such as tungsten and molybdenum). However, these methods have significant drawbacks: unmodified ceramic particles have poor interfacial compatibility with the steel matrix, easily agglomerating to form stress concentration points, leading to a decrease in the toughness of the mold steel; adding a single alloying element is unlikely to simultaneously achieve a synergistic improvement in thermal conductivity and hardness, often resulting in a trade-off. Furthermore, in the traditional mold steel manufacturing process, problems such as uneven dispersion of the reinforcing phase and poor matching of heat treatment process parameters further limit the optimization of the material's overall performance.

[0004] Therefore, there is an urgent need to develop a plastic mold steel that achieves a balance of high thermal conductivity, high hardness, and high toughness through multi-component modification synergy, optimized interface bonding, and preparation process. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a high thermal conductivity and high hardness plastic mold steel. By directional modification of three materials—nano silicon nitride, titanium alloy powder, and graphene—combined with a reasonable component ratio and preparation process, the thermal conductivity, hardness, wear resistance, and toughness of the material are synergistically improved. This invention also provides a preparation method for this mold steel, with a stable and controllable process suitable for industrial production.

[0006] Technical solution: A high thermal conductivity and high hardness plastic mold steel, comprising the following components by weight: 80 parts of 42CrMo steel matrix, 5 parts of modified nano silicon nitride, 3 parts of modified titanium alloy powder, 2 parts of modified graphene, 2 parts of ferrovanadium, 1 part of ferroniobium, 3 parts of nickel powder, 1 part of manganese powder, and 1 part of silicon powder. The 42CrMo steel matrix is ​​a high-quality alloy structural steel with the following chemical composition (mass fraction): C 0.40%, Cr 1.00%, Mo 0.20%, Si 0.30%, Mn 0.70%, P ≤ 0.03%, S ≤ 0.03%, and the balance is Fe. The modified nano-silicon nitride was modified by plasma treatment and silane coupling agent grafting, with an average particle size of 50 nm. The modified titanium alloy powder is Ti6Al4V alloy powder modified by mechanical alloying and alumina coating, with an average particle size of 10μm. The modified graphene is modified by hydrogen reduction and aminosilane grafting, with ≤5 layers and a sheet diameter of 1-3 μm. The ferrovanadium has a vanadium content of 50%, the ferroniobium has a niobium content of 60%, and the nickel powder, manganese powder, and silicon powder are all industrial grade with a purity of ≥99.5%.

[0007] Preferably, the preparation method of modified nano-silicon nitride is as follows: nano-silicon nitride is placed in a radio frequency inductively coupled plasma device, with a mixture of Ar and H2 gas at a volume ratio of 3:1 as the working gas, a power of 180W, and a treatment time of 12min, to introduce hydroxyl and amino active sites on the surface of nano-silicon nitride; the plasma-treated nano-silicon nitride is dispersed in anhydrous ethanol, and γ-aminopropyltriethoxysilane coupling agent (coupling agent to nano-silicon nitride mass ratio of 1.2:1) is added, and the reaction is stirred at 70℃ for 5h, forming a graft layer through chemical bonding between the active sites and silane groups; after the reaction is completed, the nano-silicon nitride is vacuum dried at 120℃ for 4h to obtain modified nano-silicon nitride with a surface grafting rate of 78%.

[0008] Preferably, the preparation method of modified titanium alloy powder is as follows: Ti6Al4V alloy powder and alumina powder are mixed at a mass ratio of 10:1 and added to a planetary ball mill. Stainless steel balls are used as the grinding media (ball-to-material ratio 15:1), and the rotation speed is 400 r / min. Mechanical alloying treatment is carried out for 8 hours to make the alumina particles uniformly adhere to the surface of the titanium alloy powder. Then, 3% of polyvinyl alcohol aqueous solution by mass of the mixture is added as a binder. The mixture is dried at 200℃ for 2 hours, pressed and sintered at 800℃ for 1 hour to form an alumina coating layer. After cooling, the mixture is pulverized to an average particle size of 10 μm to obtain modified titanium alloy powder with a coating layer thickness of 0.8-1.2 μm.

[0009] Preferably, the modified graphene is prepared as follows: raw graphene is placed in a tube furnace, hydrogen gas (flow rate 50 mL / min) is introduced, and it is reduced at 800 °C for 2 h to remove oxygen-containing impurities on the surface and improve conductivity; the reduced graphene is dispersed in N,N-dimethylformamide, KH550 aminosilane coupling agent (coupling agent to graphene mass ratio of 1.0:1) is added, and it is ultrasonically reacted at 65 °C for 3 h to achieve grafting through chemical bonding between the defect sites on the graphene surface and the aminosilane; after the reaction, it is centrifuged and vacuum dried at 100 °C for 3 h to obtain modified graphene with an amino content of 3.5 mmol / g on the surface.

[0010] Preferably, ferrovanadium and ferroniobium work synergistically to form V(Nb)C carbides during the smelting process, which refines the grains and improves the hardness of the material; nickel powder, manganese powder, and silicon powder are combined to improve the toughness and hardenability of the steel matrix and avoid the increase in brittleness caused by the addition of hard reinforcing phases.

[0011] A method for preparing a high thermal conductivity and high hardness plastic mold steel includes the following steps: S1. Ingredients: Accurately weigh 80 parts of 42CrMo steel matrix, 5 parts of modified nano silicon nitride, 3 parts of modified titanium alloy powder, 2 parts of modified graphene, 2 parts of ferrovanadium, 1 part of ferroniobium, 3 parts of nickel powder, 1 part of manganese powder, and 1 part of silicon powder according to the weight ratio, and set aside. S2. Mixing: Add all components to the double cone mixer, set the speed to 300 r / min, and mix for 30 minutes to ensure that the components are evenly dispersed to obtain the mixed raw material; S3, Vacuum Induction Melting: Add the mixed raw materials to the vacuum induction melting furnace and evacuate to a vacuum level of 1×10⁻⁶. -3 Pa, heat to 1550℃, hold for 3 hours, and stir every 30 minutes (stirring speed 50r / min) to ensure uniform melt composition; S4. Forging: The molten steel is poured into a mold and cooled to room temperature to obtain an ingot; the ingot is heated to 1100℃, held for 2 hours and then free forged, with a forging deformation of 60%; after forging, it is air-cooled to room temperature. S5. Heat treatment: The forged billet is quenched by heating to 850℃, holding for 2 hours, and then oil-cooled to room temperature; then tempered by heating to 550℃, holding for 3 hours, and air-cooled to room temperature to obtain the mold steel semi-finished product. S6. Precision machining: Grinding and polishing the semi-finished mold steel to obtain finished plastic mold steel with high thermal conductivity and high hardness.

[0012] Beneficial effects: This invention performs directional modification on three key materials: nano-silicon nitride, titanium alloy powder, and graphene, solving the problems of poor interfacial compatibility and easy agglomeration of traditional reinforcing phases with steel matrix. The modified nano-silicon nitride is grafted with silane through plasma treatment, which increases the density of surface active sites by more than 4 times and enhances the bonding force with the matrix interface, significantly improving the material's hardness and wear resistance. The alumina coating of the modified titanium alloy powder has both thermal conductivity and wear resistance properties, and its synergistic effect with Ti6Al4V improves the material's thermal conductivity. The hydrogen reduction and aminosilane grafting of the modified graphene constructs a continuous thermally conductive network, further optimizing the thermal conductivity.

[0013] Three modified materials, in synergy with alloying elements such as ferrovanadium and ferroniobium, achieve a balance between thermal conductivity and hardness: nano-silicon nitride and titanium alloy powder provide high hardness and wear resistance; graphene constructs thermal conductivity pathways; ferrovanadium and ferroniobium form carbides that refine grains; and nickel powder improves toughness, enabling the mold steel to simultaneously possess high thermal conductivity (≥45W / (m²)). K), high hardness (≥60HRC) and good toughness (impact toughness ≥25J / cm). 2 ).

[0014] The preparation process employs vacuum induction melting, forging, and precision heat treatment to ensure uniform dispersion of each component and densification of the microstructure. The vacuum environment prevents oxidation inclusions, forging improves the material density, and quenching and tempering processes enable the microstructure to form a uniform composite structure of tempered sorbite, carbides, and reinforcing phases, further enhancing the overall performance. Attached Figure Description

[0015] Figure 1 This is a comparison of the performance test results of the embodiments of the present invention and the comparative examples; Figure 2 This is a process flow diagram for the preparation of high thermal conductivity and high hardness plastic mold steel. Detailed Implementation

[0016] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] Example 1

[0018] (1) Preparation of modified nano-silicon nitride: 5g of nano-silicon nitride was placed in a radio frequency inductively coupled plasma device with Ar and H2 mixed gas in a volume ratio of 3:1 as the working gas, power 180W, and treatment time 12min; the treated nano-silicon nitride was dispersed in anhydrous ethanol, 6g of γ-aminopropyltriethoxysilane coupling agent was added, and the reaction was stirred at 70℃ for 5h; the nano-silicon nitride was dried under vacuum at 120℃ for 4h to obtain modified nano-silicon nitride; (2) Preparation of modified titanium alloy powder: 30g Ti6Al4V alloy powder and 3g alumina powder were mixed and added to a planetary ball mill with a ball-to-material ratio of 15:1 and a rotation speed of 400r / min. The mixture was mechanically alloyed for 8h. 1.0g polyvinyl alcohol aqueous solution was added and dried at 200℃ for 2h. After pressing and molding, the mixture was sintered at 800℃ for 1h and pulverized to an average particle size of 10μm to obtain modified titanium alloy powder. (3) Preparation of modified graphene: 2g of raw graphene was placed in a tube furnace, hydrogen flow rate was 50mL / min, and it was reduced at 800℃ for 2h; it was dispersed in N,N-dimethylformamide, 2g of KH550 aminosilane coupling agent was added, and it was ultrasonically reacted at 65℃ for 3h; after centrifugation, it was vacuum dried at 100℃ for 3h to obtain modified graphene; (4) Ingredients: Weigh out 80 parts of 42CrMo steel matrix, 5 parts of modified nano silicon nitride prepared in step (1), 3 parts of modified titanium alloy powder prepared in step (2), 2 parts of modified graphene prepared in step (3), 2 parts of ferrovanadium, 1 part of ferroniobium, 3 parts of nickel powder, 1 part of manganese powder, and 1 part of silicon powder. (5) Mixing: Add all components to a double cone mixer, mix at 300 r / min for 30 minutes to obtain a mixed raw material; (6) Vacuum induction melting: Add the mixed raw materials to the vacuum induction melting furnace and evacuate to 1×10 -3 Pa, keep warm at 1550℃ for 3 hours, stirring once every 30 minutes (50r / min); (7) Forging: molten steel is poured into a mold and cooled to obtain an ingot; it is held at 1100℃ for 2 hours, then free forged (60% deformation) and air-cooled to room temperature; (8) Heat treatment: oil quenching at 850℃ for 2 hours, and air tempering at 550℃ for 3 hours; (9) Finishing: Grinding and polishing to obtain high thermal conductivity and high hardness plastic mold steel finished products.

[0019] Example 2

[0020] (1) Preparation of modified nano-silicon nitride: Same as in Example 1, but the amount used is 8g and the amount of coupling agent is 9.6g; (2) Preparation of modified titanium alloy powder: Same as in Example 1, but the amount used is 5g, Ti6Al4V alloy powder 50g, alumina powder 5g, and polyvinyl alcohol aqueous solution 1.7g; (3) Preparation of modified graphene: Same as in Example 1, but the amount used is 3g, and KH550 aminosilane coupling agent is 3g; (4) Ingredients: Weigh out 79 parts of 42CrMo steel matrix, 8 parts of modified nano silicon nitride, 5 parts of modified titanium alloy powder, 3 parts of modified graphene, 2 parts of ferrovanadium, 1 part of ferroniobium, 3 parts of nickel powder, 1 part of manganese powder and 1 part of silicon powder by weight. (5) The steps of mixing, smelting, forging, heat treatment and finishing are the same as in Example 1.

[0021] Example 3

[0022] (1) Preparation of modified nano-silicon nitride: Same as in Example 1, but the amount used is 10g and the amount of coupling agent is 12g; (2) Preparation of modified titanium alloy powder: Same as in Example 1, but the amount used is 7g, Ti6Al4V alloy powder 70g, alumina powder 7g, and polyvinyl alcohol aqueous solution 2.3g; (3) Preparation of modified graphene: Same as in Example 1, but with a dosage of 4g and 4g of KH550 aminosilane coupling agent; (4) Ingredients: Weigh out 78 parts of 42CrMo steel matrix, 10 parts of modified nano silicon nitride, 7 parts of modified titanium alloy powder, 4 parts of modified graphene, 2 parts of ferrovanadium, 1 part of ferroniobium, 3 parts of nickel powder, 1 part of manganese powder and 1 part of silicon powder by weight. (5) The steps of mixing, smelting, forging, heat treatment and finishing are the same as in Example 1.

[0023] Comparative Example 1

[0024] Same as Example 1, except that: unmodified nano-silicon nitride (not subjected to plasma treatment and silane grafting) was used, while the other components and preparation steps were the same.

[0025] Comparative Example 2

[0026] Same as Example 1, except that no modified titanium alloy powder was added, while the other components and preparation steps are the same.

[0027] Comparative Example 3

[0028] Same as Example 1, except that: unmodified graphene (not subjected to hydrogen reduction and aminosilane grafting) is used, while the other components and preparation steps are the same.

[0029] Comparative Example 4

[0030] Same as Example 1, except that: ordinary electric arc melting is used instead of vacuum induction melting (the melting environment is atmospheric, and the other melting parameters are the same), and the other components and preparation steps are the same.

[0031] Comparative Example 5

[0032] Same as Example 1, except that the forging process is omitted (the ingot is directly heat-treated, and the remaining steps are the same), while the remaining components and preparation steps are the same.

[0033] Comparative Example 6

[0034] Same as Example 1, except that the heat treatment process is simplified (only quenching is performed, without tempering; quenching parameters: 850℃ for 2 hours, oil cooling), while the other components and preparation steps are the same.

[0035] Performance testing methods

[0036] Hardness (HRC): Tested according to GB / T231.1-2018 "Metallic materials - Brinell hardness test - Part 1: Test method"; Thermal conductivity (W / (m・K)): Tested according to GB / T3651-2008 "Method for Measurement of Thermal Conductivity of Metals at High Temperature" (test temperature 25℃); Tensile strength (MPa): Tested according to GB / T228.1-2010 "Metallic materials, tensile testing - Part 1: Test method at room temperature"; Impact toughness (J / cm²): Tested according to GB / T229-2007 "Metallic Materials Charpy Impact Test Method" (V-notch); Wear resistance (wear amount mg): Tested according to GB / T12444.2-2006 "Metallic materials wear test method part 2: dry sliding wear test" (load 50N, rotation speed 200r / min, time 2h).

[0037] Relative density (%): Tested according to GB / T29518-2013 "Method for Determination of Density of Metallic Materials", reflecting the degree of densification of the microstructure; Component segregation (%): Electron probe microanalysis (EPMA) was used to test and calculate the component fluctuation coefficient of the main reinforcing phase (nano silicon nitride). Segregation = (maximum content - minimum content) / average content × 100%, which reflects the uniformity of component dispersion.

[0038] The performance test results of the above embodiments and comparative examples are as follows: Figure 1 As shown, Examples 1-3 exhibit excellent properties: hardness reaches 62-65 HRC, and thermal conductivity is 48-55 W / (m²). K), tensile strength 1250-1300MPa, impact toughness 25-28J / cm² 2 The wear amount was only 6.8-8.5mg, indicating that the synergistic effect of the three modified materials and alloying elements was significant and the composition ratio was reasonable.

[0039] Comparative Example 1 (Unmodified Nano-Silicon Nitride): Hardness only 52 HRC, wear amount as high as 25.3 mg, thermal conductivity 35 W / (m²). Because unmodified nano-silicon nitride has poor interfacial bonding with the matrix and is prone to agglomeration, it cannot effectively enhance wear resistance and thermal conductivity, resulting in a significant decrease in performance.

[0040] Comparative Example 2 (without modified titanium alloy powder): thermal conductivity decreased to 38 W / (m The results showed that the alumina coating of the modified titanium alloy powder and Ti6Al4V had a hardness of 55HRC and a wear rate of 18.6mg, indicating that the synergistic effect of the alumina coating and Ti6Al4V was the key to improving thermal conductivity and wear resistance. The absence of these coatings significantly weakened the material properties.

[0041] Comparative Example 3 (unmodified graphene): Thermal conductivity 40 W / (m K), with a hardness of 58HRC, is difficult to construct a continuous thermally conductive network due to the large number of impurities on the surface of unmodified graphene and its poor compatibility with the matrix. Moreover, the enhancement effect is limited, and the performance is lower than that of the example.

[0042] Comparative Example 4 (Ordinary electric arc melting replacing vacuum induction melting): The relative density decreased to 97.2%, the component segregation was as high as 12.3%, and the hardness and thermal conductivity were only 56 HRC and 39 W / (m²), respectively. K). The reason is that melting under atmospheric conditions produces oxidative inclusions, and the lack of composition homogenization under vacuum conditions leads to agglomeration of the reinforcing phase and poor interfacial bonding, which verifies the key role of vacuum induction melting in avoiding oxidation and ensuring uniform dispersion of components.

[0043] Comparative Example 5 (forging process omitted): relative density 96.8%, impact toughness only 18 J / cm². 2 The tensile strength is 1020 MPa. Due to the lack of densification effect from forging, there are porosity defects inside the ingot, and the interface between the reinforcing phase and the matrix is ​​not effectively bonded, resulting in a significant decrease in the toughness and strength of the material. This proves that the forging process is the core step in improving the density of the microstructure and the interfacial bonding force.

[0044] Comparative Example 6 (simplified heat treatment, quenching only, no tempering): Although the hardness increased to 68 HRC, the impact toughness plummeted to 12 J / cm. 2 It has a tensile strength of 980 MPa, exhibiting the defect of being "hard and brittle". Because the microstructure after quenching is martensitic and it has not undergone tempering to relieve internal stress, it has extremely poor toughness and cannot meet the actual use requirements of mold steel. This highlights the importance of precise heat treatment of "quenching + tempering" for balancing hardness and toughness.

[0045] In summary, this invention, through the directional modification of nano-silicon nitride, titanium alloy powder, and graphene, combined with a reasonable component ratio and preparation process, successfully prepared a plastic mold steel with high thermal conductivity, high hardness, high toughness, and high wear resistance. This solves the performance shortcomings of traditional mold steel and is suitable for the plastic injection molding field where high molding precision and production efficiency are required.

[0046] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A high thermal conductivity and high hardness plastic mold steel, characterized in that, The composition by weight is as follows: 80 parts of 42CrMo steel matrix, 5 parts of modified nano silicon nitride, 3 parts of modified titanium alloy powder, 2 parts of modified graphene, 2 parts of ferrovanadium, 1 part of ferroniobium, 3 parts of nickel powder, 1 part of manganese powder, and 1 part of silicon powder. The 42CrMo steel matrix is ​​an alloy structural steel, and its chemical composition by mass fraction includes: C 0.40%, Cr 1.00%, Mo 0.20%, Si 0.30%, Mn 0.70%, P ≤ 0.03%, S ≤ 0.03%, with the balance being Fe; The modified nano-silicon nitride was modified by plasma treatment and silane coupling agent grafting, with an average particle size of 50 nm. The modified titanium alloy powder is Ti6Al4V alloy powder modified by mechanical alloying and alumina coating, with an average particle size of 10μm. The modified graphene is modified by hydrogen reduction and aminosilane grafting, with ≤5 layers and a sheet diameter of 1-3 μm. The ferrovanadium has a vanadium content of 50%, the ferroniobium has a niobium content of 60%, and the nickel powder, manganese powder, and silicon powder are all industrial grade with a purity of ≥99.5%.

2. The high thermal conductivity and high hardness plastic mold steel according to claim 1, characterized in that, The modified nano-silicon nitride is prepared as follows: nano-silicon nitride is placed in a radio frequency inductively coupled plasma device, with a mixture of Ar and H2 gas at a volume ratio of 3:1 as the working gas, a power of 180W, and a treatment time of 12min to introduce hydroxyl and amino active sites on the surface of nano-silicon nitride; the plasma-treated nano-silicon nitride is dispersed in anhydrous ethanol, and γ-aminopropyltriethoxysilane coupling agent is added at a ratio of 1.2:

1. The mixture is stirred and reacted at 70℃ for 5h to form a graft layer through chemical bonding between the active sites and silane groups; after the reaction is completed, the mixture is vacuum dried at 120℃ for 4h to obtain modified nano-silicon nitride.

3. The high thermal conductivity and high hardness plastic mold steel according to claim 1, characterized in that, The modified titanium alloy powder is prepared as follows: Ti6Al4V alloy powder and alumina powder are mixed at a mass ratio of 10:1 and added to a planetary ball mill. Stainless steel balls are used as the grinding medium, the ball-to-material ratio is 15:1, the rotation speed is 400 r / min, and mechanical alloying is performed for 8 hours to make the alumina particles uniformly adhere to the surface of the titanium alloy powder. Then, 3% polyvinyl alcohol aqueous solution is added as a binder, dried at 200℃ for 2 hours, pressed and sintered at 800℃ for 1 hour to form an alumina coating layer. After cooling, it is pulverized to an average particle size of 10 μm to obtain modified titanium alloy powder with a coating layer thickness of 0.8-1.2 μm.

4. The high thermal conductivity and high hardness plastic mold steel according to claim 1, characterized in that, The modified graphene is prepared as follows: raw graphene is placed in a tube furnace, hydrogen is introduced at a flow rate of 50 mL / min, and it is reduced at 800 °C for 2 h to remove oxygen-containing impurities on the surface and improve conductivity; the reduced graphene is dispersed in N,N-dimethylformamide, KH550 aminosilane coupling agent is added, the mass ratio of coupling agent to graphene is 1.0:1, and it is ultrasonically reacted at 65 °C for 3 h to achieve grafting through chemical bonding between the defect sites on the graphene surface and the aminosilane; after the reaction, it is centrifuged and vacuum dried at 100 °C for 3 h to obtain modified graphene with an amino content of 3.5 mmol / g on the surface.

5. The high thermal conductivity and high hardness plastic mold steel according to claim 1, characterized in that, The ferrovanadium and ferroniobium work synergistically to form V(Nb)C carbides during the smelting process, which refines the grains and increases the hardness of the material. Nickel powder, manganese powder, and silicon powder work together to improve the toughness and hardenability of the steel matrix and avoid the increase in brittleness caused by the addition of hard reinforcing phases.

6. A method for preparing high thermal conductivity and high hardness plastic mold steel as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Ingredients: Accurately weigh 80 parts of 42CrMo steel matrix, 5 parts of modified nano silicon nitride, 3 parts of modified titanium alloy powder, 2 parts of modified graphene, 2 parts of ferrovanadium, 1 part of ferroniobium, 3 parts of nickel powder, 1 part of manganese powder, and 1 part of silicon powder according to the weight ratio, and set aside. S2. Mixing: Add all components to the double cone mixer, set the speed to 300 r / min, and mix for 30 minutes to ensure that the components are evenly dispersed to obtain the mixed raw material; S3, Vacuum Induction Melting: Add the mixed raw materials to the vacuum induction melting furnace and evacuate to a vacuum level of 1×10⁻⁶. -3 Pa, heat to 1550℃, hold for 3 hours, and stir every 30 minutes at a speed of 50 r / min to ensure uniform melt composition; S4. Forging: The molten steel is poured into a mold and cooled to room temperature to obtain an ingot; the ingot is heated to 1100℃, held for 2 hours and then free forged, with a forging deformation of 60%; after forging, it is air-cooled to room temperature. S5. Heat treatment: The forged billet is quenched by heating to 850℃, holding for 2 hours, and then oil-cooled to room temperature; then tempered by heating to 550℃, holding for 3 hours, and air-cooled to room temperature to obtain the mold steel semi-finished product. S6. Precision machining: Grinding and polishing the semi-finished mold steel to obtain finished plastic mold steel with high thermal conductivity and high hardness.

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