A method for preparing a high-strength, impact-resistant cold heading die

Abstract

The present application relates to the technical field of alloy, in particular to a high-strength, impact-resistant hard alloy cold heading die preparation method. It aims to improve the anti-chipping and anti-radial cracking ability of the die lip and the working zone under high impact cold heading conditions. The die includes an outer working zone surrounding the die cavity and located in the corresponding area of the lip and the working zone, and a core bearing zone located outside the outer working zone, both of which are sintered integrally. The outer working zone adopts a tungsten carbide nano / micro powder compound system, through two-stage cobalt-containing precursor coating, and introduces ionic cerium source and particulate cerium source at different solid contents in sections, and adjusts the grain and binder phase distribution with vanadium carbide; the core bearing zone adopts a tungsten carbide micro powder-cobalt powder system. The die is prepared by partitioning die pressing, dewaxing, liquid phase sintering and argon pressure sintering, and is suitable for high load and high frequency cold heading forming.

Description

Technical Field

[0001] This invention relates to the field of alloy technology, and in particular to a method for preparing a high-strength, impact-resistant cemented carbide cold heading die. Background Technology

[0002] In the field of cold heading, especially in high-load, high-frequency manufacturing scenarios such as high-strength steel fasteners and irregularly shaped nuts, mold failure is a key bottleneck restricting production efficiency and cost. Existing cold heading molds generally use tungsten-cobalt (WC-Co) cemented carbide, and their performance control mainly relies on macroscopic adjustments to cobalt content, tungsten carbide grain size, and its gradation. This traditional approach typically follows a trade-off between strength and toughness: increasing cobalt content sacrifices some hardness and strength for toughness, or decreasing cobalt content increases hardness and compressive strength, but inevitably carries the risk of brittleness due to decreased toughness. This "one gain, one loss" effect becomes increasingly limiting when facing high-strength, high-impact cold heading conditions.

[0003] In actual service, especially in high-stress concentration areas such as the die lip and working zone, crack initiation and rapid propagation become the main failure modes. This is primarily because traditional homogeneous mixing and conventional sintering processes make it difficult to precisely control the cobalt binder phase within the microstructure. The cobalt phase is often randomly and non-uniformly distributed within the tungsten carbide framework, easily forming localized enrichment or segregation. Under high-frequency impact loads, these cobalt-enriched areas become stress concentration points and weak points where cracks preferentially initiate, leading to early-stage localized corner collapse, edge chipping, or radial through-cracks in the die, severely impacting the die's service life and product dimensional stability.

[0004] To improve toughness, existing technologies introduce carbide inhibitors such as vanadium carbide (VC) or rare earth oxides, but these are typically achieved through a simple one-time mixing with the main powder. This "back-end addition, overall uniform distribution" strategy, while able to suppress abnormal grain growth to some extent, fails to fundamentally optimize the initial distribution and migration path of the cobalt phase, thus having limited effect on strengthening key load-bearing interfaces. Furthermore, the conventional "one-step" addition method results in an overly singular role for the additives during sintering, failing to provide temporal and spatial synergy according to the needs of different stages (such as interface purification and grain boundary pinning). This leads to a bottleneck in performance improvement, making it difficult to simultaneously achieve substantial breakthroughs in toughness and crack propagation resistance while maintaining high hardness. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a method for preparing a high-strength, impact-resistant cemented carbide cold heading die, so as to solve the technical problem in the prior art that it is difficult to achieve high toughness and excellent crack propagation resistance at the same time under the premise of high hardness by simply adjusting the cobalt content and additives, which leads to the cold heading die being prone to early chipping and radial cracks in the lip area under high impact conditions.

[0006] To achieve the above objectives, the present invention provides a method for preparing a high-strength, impact-resistant cemented carbide cold heading die, comprising the following steps:

[0007] S1. Preparation of outer working zone powder: Tungsten carbide nanoparticles are dispersed and coated with a cobalt-containing precursor in the first stage, followed by the addition of vanadium carbide and tungsten carbide microparticles for a second stage of cobalt-containing precursor coating; when the slurry solid content reaches 48wt%-52wt%, an ionic cerium source is added, and when the slurry solid content reaches 56wt%-60wt%, a particulate cerium source and a portion of polyethylene glycol 600 are added; subsequently, the slurry is concentrated under reduced pressure, dried, reduced, and ball-milled to obtain the outer working zone powder; the remaining polyethylene glycol 600, graphite powder, and paraffin are added during the ball milling process;

[0008] S2. Preparation of core support area powder: Tungsten carbide micro powder and cobalt powder are mixed and ball-milled to obtain core support area powder;

[0009] S3. Partitioned molding and pressing: Using a core rod mold, the outer working area powder is first laid around the core rod and in the corresponding parts of the mold lip and working belt after molding and pre-pressed. Then, the core bearing area powder is added for final pressing to obtain the pressed blank.

[0010] S4. Sintering: The pressed blank is dewaxed, liquid phase sintered and argon pressure sintering is performed to obtain a high-strength, impact-resistant cemented carbide cold heading die;

[0011] The resulting high-strength, impact-resistant cemented carbide cold heading die includes an outer working area and a core bearing area. The outer working area surrounds the mold cavity of the cold heading die and is located in the area corresponding to the mold lip and the working zone. The core bearing area is located on the side of the outer working area away from the mold cavity, and the outer working area and the core bearing area are sintered and integrally formed.

[0012] Preferably, in step S1, the raw materials for preparing the outer working area powder, by mass parts, include: 80-100 parts of tungsten carbide nanopowder, 100-120 parts of first-stage cobalt source, 160-200 parts of tungsten carbide micropowder, 35-45 parts of second-stage cobalt source, 1-3 parts of vanadium carbide, 1-3 parts of ionic cerium source, 0.5-1.5 parts of particulate cerium source, 3-7 parts of polyethylene glycol 600, 1 part of graphite powder, and 3-5 parts of paraffin wax; in step S2, the raw materials for preparing the core bearing area powder, by mass parts, include: 600-640 parts of tungsten carbide micropowder and 65-75 parts of cobalt powder.

[0013] Preferably, the first-stage cobalt source and the second-stage cobalt source are both cobalt nitrate hexahydrate, the ionic cerium source is cerium nitrate hexahydrate, and the particulate cerium source is cerium oxide nanoparticles.

[0014] Preferably, the first-stage cobalt-containing precursor is formed by reacting 100-120 parts of a first-stage cobalt source with 46-54 parts of oxalate dihydrate, and the second-stage cobalt-containing precursor is formed by reacting 35-45 parts of a second-stage cobalt source with 16-20 parts of oxalate dihydrate.

[0015] Preferably, the tungsten carbide nanopowder has a particle size of 150nm-200nm, the tungsten carbide micropowder has a particle size of 2μm, the cobalt powder has a particle size of 2μm, the vanadium carbide has a particle size of less than 2μm, the cerium oxide nanopowder has a particle size of less than 50nm, and the graphite powder has a particle size of less than 20μm.

[0016] Preferably, in step S1, the reduction is as follows: first, argon gas is introduced and the temperature is increased to 245-260°C at 2-2.5°C / min, and held for 50-70 min; then, hydrogen gas is introduced, and the temperature is increased to 345-360°C at 3-3.5°C / min and held for 50-70 min; then, the temperature is increased to 445-460°C at 2°C / min and held for 110-140 min; and finally, the temperature is cooled to room temperature and removed.

[0017] Preferably, in step S1, ball milling is performed by wet ball milling at 145-160 rpm for 2.5-4 hours at a ball-to-material mass ratio of 4:1; in step S2, ball milling is performed by wet ball milling at 175-190 rpm for 7-9 hours at a ball-to-material mass ratio of 5:1.

[0018] Preferably, in step S3, the outer working area powder is first evenly spread around the core rod and the parts corresponding to the mold lip and working belt after molding, and then pre-pressed at 55-70MPa after 18-25s vibration; then the core bearing area powder is added, and the final pressure is 215-230MPa and held for 60-70s to obtain the pressed blank.

[0019] Preferably, in step S4, the pressed blank is placed in a vacuum sintering furnace. Under a vacuum degree not exceeding 10 Pa, the temperature is increased to 275-290℃ at 0.9-1.2℃ / min and held for 55-70 min. Then, the temperature is increased to 440-470℃ at 1.4-1.8℃ / min and held for 85-100 min for dewaxing. Subsequently, the temperature is increased to 1175-1190℃ at 4℃ / min and held for 18-25 min. Then, the temperature is increased to 1275-1290℃ at 2℃ / min and held for 10-12 min. Finally, the temperature is increased to 1375-1390℃ at 3℃ / min and held for 42-50 min to complete liquid phase sintering. The temperature is then switched to 4-6 MPa argon gas for 12-20 min, and then the temperature is reduced to 1240-1270℃ at 4-5℃ / min and cooled with the furnace.

[0020] Preferably, in step S1, the first-stage cobalt source solution is first added to the tungsten carbide nanopowder slurry, and then the first-stage oxalic acid solution prepared by oxalic acid dihydrate is added to perform the first-stage cobalt-containing precursor coating; after the first-stage cobalt-containing precursor coating is completed, vanadium carbide is added first, followed by tungsten carbide micropowder, and the second-stage cobalt-containing precursor coating is performed in the order of first adding the second-stage cobalt source solution and then adding the second-stage oxalic acid solution prepared by oxalic acid dihydrate.

[0021] The beneficial effects of this invention are:

[0022] (1) This invention achieves precise timing control of the formation position, migration path and final distribution of the cobalt binder phase through a continuous process chain of "two-stage coating, intercalation of vanadium carbide, and segmented introduction of dual cerium sources". This design enables the mold to form a continuous, uniform and unsaturated tough cobalt phase network in the surface impact zone in the final microstructure, while the core maintains a high-strength support skeleton, thereby synergistically improving the transverse fracture strength and impact toughness of the material at the microscopic level, and effectively suppressing the initiation and rapid propagation of cracks.

[0023] (2) This invention creatively combines the cobalt phase gradient distribution with the functional partitioning pressing process of the "outer working area - core bearing area". Through spatial mold design, the powder with optimized structure prepared by the above method is oriented and configured in the lip and working zone areas of the mold that are most prone to failure, so that the advantages of the material structure are precisely applied to the parts where the service stress is most concentrated. This is not a simple component optimization, but a precise spatial matching between the advantages of the material structure and the service stress field of the mold, which ultimately significantly improves the actual service life of the mold.

[0024] (3) The synergistic modification mechanism of the present invention has a nonlinear superposition effect. Compared with the scheme in the comparative example that omits any key step, the embodiment of the present invention achieves significant and simultaneous improvement in transverse fracture strength, impact toughness and mold life while maintaining high hardness (about 89.5 HRA). Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0026] The raw materials are as follows: Tungsten carbide nanopowder is Sigma-Aldrich, product number 778346, hexagonal, particle size 150nm-200nm, purity ≥99%; Tungsten carbide micropowder is Sigma-Aldrich, product number 241881, particle size 2μm, purity ≥99%; Cobalt powder is Sigma-Aldrich, product number 266639, particle size 2μm, purity 99.8%; Vanadium carbide is Sigma-Aldrich, product number 745847, particle size <2μm, purity 99.9%; Cerium oxide nanopowder is Sigma-Aldrich, product number 700290, particle size <50nm, specific surface area 30m². 2 / g, purity 99.95%; graphite powder is Sigma-Aldrich, item number 282863, particle size <20μm; paraffin is Sigma-Aldrich, item number 76242, freezing point 54℃-56℃.

[0027] Example 1:

[0028] Step 1: Add 700 mL of anhydrous ethanol and 100 mL of deionized water to a jacketed reaction vessel with mechanical stirring. Add 90 g of tungsten carbide nanoparticles and disperse under ultrasonic conditions at 40 kHz for 20 min. Then, mechanically stir at 400 rpm at 35 °C to form a uniform slurry. Separately, dissolve 110 g of cobalt nitrate hexahydrate in 120 mL of deionized water to obtain the first-stage cobalt salt solution. Add 50 g of oxalic acid dihydrate to 400 mL of deionized water and stir in a water bath at 45 °C until completely clear to obtain the first-stage oxalic acid solution. First, add the first-stage cobalt salt solution to the tungsten carbide nanoparticle slurry at a uniform rate over 10 min. Then, add the first-stage oxalic acid solution dropwise over 30 min. After the dropwise addition is complete, continue stirring at 35 °C for 45 min to allow the cobalt-containing precursor to preferentially deposit on the surface of the nano-sized tungsten carbide particles.

[0029] Step 2: Add 80 mL of anhydrous ethanol to another container, add 2 g of vanadium carbide, and disperse under ultrasonic conditions at 40 kHz for 10 min. Then slowly add it to the slurry obtained in Step 1 and continue stirring for 20 min. Next, add 180 g of tungsten carbide micro powder to the system to form a nano / micro composite tungsten carbide slurry. Separately, dissolve 40 g of cobalt nitrate hexahydrate in 50 mL of deionized water to obtain the second-stage cobalt salt solution. Add 18 g of oxalic acid dihydrate to 150 mL of deionized water and stir in a 45 °C water bath until completely clear to obtain the second-stage oxalic acid solution. Implement the second-stage coating by adding the second-stage cobalt salt solution first, followed by the second-stage oxalic acid solution. After all the additions are completed, continue stirring at 35 °C for 40 min.

[0030] Step 3: The slurry obtained in Step 2 was concentrated under reduced pressure at 55℃ and 0.08MPa. Every 20 minutes, 5g of slurry samples were taken and dried in an oven at 105℃ until constant weight. The solid content was calculated as the percentage of dry weight to the total sample weight. When the solid content reached 50wt%, 2g of cerium nitrate hexahydrate was dissolved in 20mL of deionized water and added dropwise to the slurry over 10 minutes. After the addition was completed, stirring was continued for 20 minutes. Then, the slurry was concentrated under reduced pressure until the solid content reached 58wt%. 1g of cerium oxide nanopowder and 2g of polyethylene glycol 600 were added to 50mL of anhydrous ethanol and dispersed under ultrasonic conditions at 40kHz for 10 minutes to obtain a particulate cerium source dispersion. This dispersion was then added to the slurry and stirred for 15 minutes.

[0031] Step 4: Spread the wet material obtained in Step 3 evenly in a PTFE tray with a thickness not exceeding 10 mm. After vacuum drying at 80℃ for 12 hours, break it up and pass it through a 40-mesh sieve. Load the resulting powder into a quartz boat and place it in a tube furnace. First, purge the atmosphere with high-purity argon gas for 30 minutes, then raise the temperature to 250℃ at 2℃ / min and hold for 60 minutes. Next, switch to high-purity hydrogen gas, raise the temperature to 350℃ at 3℃ / min and hold for 60 minutes, then raise the temperature to 40-mesh sieve at 2℃ / min. The cobalt-containing precursor was decomposed and reduced to the cobalt phase by holding it at 50℃ for 120 min. After cooling to room temperature, it was taken out under high-purity argon protection. 1g of graphite powder, 3g of polyethylene glycol 600, 4g of paraffin and 150mL of anhydrous ethanol were added to the reduced powder. The powder was wet-milled at 150rpm for 3h in a cemented carbide ball mill jar and cemented carbide balls at a ball-to-material mass ratio of 4:1. After pouring out the slurry, it was vacuum dried at 60℃ for 8h, dispersed and passed through a 60-mesh sieve to obtain the outer working area powder.

[0032] Step 5: Add 620g of tungsten carbide micro powder, 70g of cobalt powder, 1g of graphite powder, 4g of polyethylene glycol 600, 6g of paraffin wax and 300mL of anhydrous ethanol to a cemented carbide ball milling jar. Wet ball mill at 180rpm for 8h under the condition that the mass ratio of cemented carbide balls to powder is 5:1. After pouring out, vacuum dry at 60℃ for 10h, break up and pass through a 60-mesh sieve to obtain the core carrier powder.

[0033] Step 6: Use the core rod mold to partition the mold. First, evenly spread 305g of outer working area powder around the core rod and the corresponding future mold lip and working zone. After compacting for 20s, pre-press at 60MPa. Then add 691g of core bearing powder, and finally press at 220MPa for 60s to obtain the pre-molded cavity blank.

[0034] Step 7: Place the pressed blank obtained in Step 6 into a vacuum sintering furnace. Under a vacuum degree not exceeding 10 Pa, heat the blank to 280°C at 1°C / min and hold for 60 min. Then heat the blank to 450°C at 1.5°C / min and hold for 90 min to complete dewaxing. Then heat the blank to 1180°C at 4°C / min and hold for 20 min. Then heat the blank to 1280°C at 2°C / min and hold for 10 min. Finally heat the blank to 1380°C at 3°C / min and hold for 45 min to complete liquid phase sintering. After the sintering and holding period, switch to 5 MPa argon gas and hold for 15 min. Then cool the blank to 1250°C at 4°C / min and cool it with the furnace to obtain a high-strength, impact-resistant cemented carbide cold heading die.

[0035] Example 2:

[0036] Step 1: Add 680 mL of anhydrous ethanol and 90 mL of deionized water to a reaction vessel, add 80 g of tungsten carbide nanoparticles, disperse under ultrasonic conditions at 40 kHz for 20 min, and then mechanically stir at 380 rpm at 34 °C to form a uniform slurry. Separately, dissolve 100 g of cobalt nitrate hexahydrate in 110 mL of deionized water to obtain the first-stage cobalt salt solution. Add 46 g of oxalic acid dihydrate to 380 mL of deionized water and stir in a water bath at 45 °C until completely clear to obtain the first-stage oxalic acid solution. First, add the first-stage cobalt salt solution over 10 min, and then add the first-stage oxalic acid solution dropwise over 28 min. After the addition is complete, continue stirring at 34 °C for 45 min.

[0037] Step 2: Add 70 mL of anhydrous ethanol to another container, add 1 g of vanadium carbide, disperse under 40 kHz ultrasonic conditions for 10 min, and then slowly add it to the slurry obtained in Step 1. Continue stirring for 20 min. Then add 160 g of tungsten carbide micro powder, and dissolve 35 g of cobalt nitrate hexahydrate in 45 mL of deionized water to obtain the second-stage cobalt salt solution. Add 16 g of oxalic acid dihydrate to 140 mL of deionized water and stir in a 45 °C water bath until completely clear to obtain the second-stage oxalic acid solution. Implement the second-stage coating by adding the second-stage cobalt salt solution first and then the second-stage oxalic acid solution. After all the additions are completed, continue stirring for 35 min.

[0038] Step 3: The slurry obtained in Step 2 was concentrated under reduced pressure at 54℃ and 0.08MPa. Every 20 minutes, 5g of slurry samples were taken and dried in an oven at 105℃ until constant weight. The solid content was calculated as the percentage of dry weight to the total sample weight. When the solid content reached 48wt%, 1g of cerium nitrate hexahydrate was dissolved in 15mL of deionized water and added dropwise to the slurry over 8 minutes. After the addition was completed, stirring was continued for 20 minutes. Then, the slurry was concentrated under reduced pressure until the solid content reached 56wt%. 0.5g of cerium oxide nanopowder and 1g of polyethylene glycol 600 were added to 40mL of anhydrous ethanol and dispersed under ultrasonic conditions at 40kHz for 10 minutes. The mixture was then added to the slurry and stirred for another 15 minutes.

[0039] Step 4: Spread the wet material obtained in Step 3 evenly in a polytetrafluoroethylene tray, vacuum dry at 78℃ for 12 hours, then break it up and pass it through a 40-mesh sieve. Load the resulting powder into a quartz boat and place it in a tube furnace. First, purge the atmosphere with high-purity argon gas for 30 minutes, then raise the temperature to 245℃ at 2℃ / min and hold for 50 minutes. Next, switch to high-purity hydrogen gas, raise the temperature to 345℃ at 3℃ / min and hold for 50 minutes, then raise the temperature again at 2℃ / min... The powder was heated to 445℃ and held for 110 minutes. After cooling to room temperature, it was taken out under high-purity argon protection. 1g of graphite powder, 2g of polyethylene glycol 600, 3g of paraffin and 130mL of anhydrous ethanol were added to the reduced powder. The powder was wet-milled in a cemented carbide ball mill jar and cemented carbide balls at a ball-to-material mass ratio of 4:1 at 145rpm for 3 hours. After pouring out, it was vacuum dried at 58℃ for 8 hours, dispersed and passed through a 60-mesh sieve to obtain the outer working area powder.

[0040] Step 5: Add 640g of tungsten carbide micro powder, 65g of cobalt powder, 1g of graphite powder, 3g of polyethylene glycol 600, 5g of paraffin wax and 280mL of anhydrous ethanol to a cemented carbide ball milling jar. Wet ball mill at 175rpm for 8h under the condition that the mass ratio of cemented carbide balls to powder is 5:1. After pouring out, vacuum dry at 60℃ for 10h, break up and pass through a 60-mesh sieve to obtain the core carrier powder.

[0041] Step 6: Use the core rod mold to partition the mold. First, evenly spread 292g of outer working area powder around the core rod and the corresponding future mold lip and working zone. After compacting for 18s, pre-press at 55MPa. Then add 694g of core bearing powder, and finally press at 215MPa for 60s to obtain the pre-formed mold cavity blank.

[0042] Step 7: Place the pressed blank obtained in Step 6 into a vacuum sintering furnace. Under a vacuum degree not exceeding 10 Pa, heat the blank to 275°C at 0.9°C / min and hold for 55 min. Then heat the blank to 440°C at 1.4°C / min and hold for 85 min to complete dewaxing. Then heat the blank to 1175°C at 4°C / min and hold for 20 min. Then heat the blank to 1275°C at 2°C / min and hold for 10 min. Finally heat the blank to 1375°C at 3°C / min and hold for 45 min to complete liquid phase sintering. After the sintering and holding period, switch to 4 MPa argon gas and hold for 15 min. Then cool the blank to 1240°C at 4°C / min and cool it with the furnace to obtain a high-strength, impact-resistant cemented carbide cold heading die.

[0043] Example 3:

[0044] Step 1: Add 720 mL of anhydrous ethanol and 120 mL of deionized water to a reaction vessel, add 100 g of tungsten carbide nanoparticles, and disperse under ultrasonic conditions at 40 kHz for 22 min. Then, mechanically stir at 420 rpm at 36 °C to form a uniform slurry. Separately, dissolve 120 g of cobalt nitrate hexahydrate in 130 mL of deionized water to obtain the first-stage cobalt salt solution. Add 54 g of oxalic acid dihydrate to 420 mL of deionized water and stir in a water bath at 45 °C until completely clear to obtain the first-stage oxalic acid solution. First, add the first-stage cobalt salt solution over 12 min, and then add the first-stage oxalic acid solution dropwise over 32 min. After the dropwise addition is complete, continue stirring at 36 °C for 50 min.

[0045] Step 2: Add 90 mL of anhydrous ethanol to another container, add 3 g of vanadium carbide, disperse under 40 kHz ultrasonic conditions for 10 min, and then slowly add it to the slurry obtained in Step 1. Continue stirring for 20 min. Then add 200 g of tungsten carbide micro powder, and dissolve 45 g of cobalt nitrate hexahydrate in 55 mL of deionized water to obtain the second-stage cobalt salt solution. Add 20 g of oxalic acid dihydrate to 160 mL of deionized water and stir in a 45 °C water bath until completely clear to obtain the second-stage oxalic acid solution. Implement the second-stage coating by adding the second-stage cobalt salt solution first, followed by the second-stage oxalic acid solution. After all the additions are completed, continue stirring for 45 min.

[0046] Step 3: The slurry obtained in Step 2 was concentrated under reduced pressure at 56℃ and 0.08MPa. Every 20 minutes, 5g of slurry samples were taken and dried in an oven at 105℃ until constant weight. The solid content was calculated as the percentage of dry weight to the total sample weight. When the solid content reached 52wt%, 3g of cerium nitrate hexahydrate was dissolved in 25mL of deionized water and added dropwise to the slurry over 12 minutes. After the addition was completed, stirring was continued for 25 minutes. Then, the slurry was concentrated under reduced pressure until the solid content reached 60wt%. 1.5g of cerium oxide nanopowder and 3g of polyethylene glycol 600 were added to 60mL of anhydrous ethanol and dispersed under ultrasonic conditions at 40kHz for 10 minutes. The mixture was then added to the slurry and stirred for another 20 minutes.

[0047] Step 4: Spread the wet material obtained in Step 3 evenly in a PTFE tray, vacuum dry at 82℃ for 12 hours, then break it up and pass it through a 40-mesh sieve. Load the resulting powder into a quartz boat and place it in a tube furnace. First, purge the atmosphere with high-purity argon for 30 minutes, then raise the temperature to 255℃ at 2℃ / min and hold for 60 minutes. Then switch to high-purity hydrogen, raise the temperature to 355℃ at 3℃ / min and hold for 60 minutes, then raise the temperature again at 2℃ / min... The powder was heated to 455℃ and held for 130 minutes. After cooling to room temperature, it was taken out under high-purity argon protection. 1g of graphite powder, 4g of polyethylene glycol 600, 5g of paraffin and 170mL of anhydrous ethanol were added to the reduced powder. The powder was wet-milled in a cemented carbide ball mill jar and cemented carbide balls at a ball-to-material mass ratio of 4:1 at 155rpm for 3 hours. After pouring out, it was vacuum dried at 62℃ for 8 hours, dispersed and passed through a 60-mesh sieve to obtain the outer working area powder.

[0048] Step 5: Add 600g of tungsten carbide micro powder, 75g of cobalt powder, 1g of graphite powder, 5g of polyethylene glycol 600, 7g of paraffin wax and 320mL of anhydrous ethanol to a cemented carbide ball milling jar. Wet ball mill at 185rpm for 8h under the condition that the mass ratio of cemented carbide balls to powder is 5:1. After pouring out, vacuum dry at 62℃ for 10h, disperse and pass through a 60-mesh sieve to obtain the core carrier powder.

[0049] Step 6: Use the core rod mold to partition the mold. First, evenly spread 318g of outer working area powder around the core rod and the corresponding future mold lip and working zone. After compaction for 22s, pre-press at 65MPa. Then add 688g of core bearing powder, and finally press at 225MPa for 65s to obtain the pre-molded cavity blank.

[0050] Step 7: Place the compact obtained in Step 6 in a vacuum sintering furnace. Under a vacuum degree not exceeding 10 Pa, heat the compact to 285°C at 1.1°C / min and hold for 65 min. Then heat it to 460°C at 1.6°C / min and hold for 95 min to complete dewaxing. Subsequently, heat the compact to 1185°C at 4°C / min and hold for 22 min. Then heat it to 1285°C at 2°C / min and hold for 10 min. Finally, heat the compact to 1385°C at 3°C / min and hold for 48 min to complete liquid phase sintering. After the sintering and holding period, switch to 6 MPa argon gas and hold for 15 min. Then cool the compact to 1260°C at 4°C / min and cool it with the furnace to obtain a high-strength, impact-resistant cemented carbide cold heading die.

[0051] Example 4:

[0052] Step 1: Add 650 mL of anhydrous ethanol and 100 mL of deionized water to a reaction vessel, add 85 g of tungsten carbide nanoparticles, disperse under ultrasonic conditions at 40 kHz for 18 min, and then mechanically stir at 360 rpm at 35 °C to form a uniform slurry. Separately, dissolve 105 g of cobalt nitrate hexahydrate in 115 mL of deionized water to obtain the first-stage cobalt salt solution. Add 48 g of oxalic acid dihydrate to 390 mL of deionized water and stir in a water bath at 45 °C until completely clear to obtain the first-stage oxalic acid solution. First, add the first-stage cobalt salt solution over 9 min, and then add the first-stage oxalic acid solution dropwise over 30 min. After the addition is complete, continue stirring at 35 °C for 40 min.

[0053] Step 2: Add 60 mL of anhydrous ethanol to another container, add 2 g of vanadium carbide, disperse under 40 kHz ultrasonic conditions for 10 min, and then slowly add it to the slurry obtained in Step 1. Continue stirring for 20 min. Then add 170 g of tungsten carbide micro powder, and dissolve 38 g of cobalt nitrate hexahydrate in 50 mL of deionized water to obtain the second-stage cobalt salt solution. Add 17 g of oxalic acid dihydrate to 145 mL of deionized water and stir in a 45 °C water bath until completely clear to obtain the second-stage oxalic acid solution. Implement the second-stage coating by adding the second-stage cobalt salt solution first, followed by the second-stage oxalic acid solution. After all the additions are completed, continue stirring for 40 min.

[0054] Step 3: The slurry obtained in Step 2 was concentrated under reduced pressure at 55℃ and 0.08MPa. Every 20 minutes, 5g of slurry samples were taken and dried in an oven at 105℃ until constant weight. The solid content was calculated as the percentage of dry weight to the total sample weight. When the solid content reached 50wt%, 2g of cerium nitrate hexahydrate was dissolved in 20mL of deionized water and added dropwise to the slurry over 10 minutes. After the addition was completed, stirring was continued for 20 minutes. Then, the slurry was concentrated under reduced pressure until the solid content reached 57wt%. 1g of cerium oxide nanopowder and 2g of polyethylene glycol 600 were added to 45mL of anhydrous ethanol and dispersed under ultrasonic conditions at 40kHz for 10 minutes. The mixture was then added to the slurry and stirred for another 15 minutes.

[0055] Step 4: Spread the wet material obtained in Step 3 evenly in a polytetrafluoroethylene tray, vacuum dry at 80℃ for 10 hours, then break it up and pass it through a 40-mesh sieve. Load the resulting powder into a quartz boat and place it in a tube furnace. First, purge the atmosphere with high-purity argon gas for 30 minutes, then raise the temperature to 250℃ at 2℃ / min and hold for 55 minutes. Subsequently, switch to high-purity hydrogen gas, raise the temperature to 350℃ at 3℃ / min and hold for 55 minutes, then raise the temperature again at 2℃ / min. The powder was heated to 450℃ for 120 minutes, cooled to room temperature, and then protected with high-purity argon gas before being removed. 1g of graphite powder, 3g of polyethylene glycol 600, 4g of paraffin wax, and 150mL of anhydrous ethanol were added to the reduced powder. The powder was then wet-milled at 150rpm for 2.5h in a cemented carbide ball mill jar and cemented carbide balls at a ball-to-powder mass ratio of 4:1. After being poured out, the powder was vacuum-dried at 60℃ for 8h, dispersed, and passed through a 60-mesh sieve to obtain the outer working area powder.

[0056] Step 5: Add 630g of tungsten carbide micro powder, 68g of cobalt powder, 1g of graphite powder, 4g of polyethylene glycol 600, 6g of paraffin wax and 300mL of anhydrous ethanol to a cemented carbide ball milling jar. Wet ball mill at 180rpm for 7h under the condition that the mass ratio of cemented carbide balls to powder is 5:1. After pouring out, vacuum dry at 60℃ for 9h, disperse and pass through a 60-mesh sieve to obtain the core carrier powder.

[0057] Step Six: Use a core rod mold to partition the mold. First, evenly spread 300g of outer working area powder around the core rod and the corresponding future mold lip and working zone. After compacting for 20s, pre-press at 60MPa. Then add 690g of core bearing powder, and finally press at 220MPa for 60s to obtain the pre-molded cavity blank.

[0058] Step 7: Place the compact obtained in Step 6 in a vacuum sintering furnace. Under a vacuum degree not exceeding 10 Pa, heat the compact to 280°C at 1°C / min and hold for 60 min. Then heat it to 450°C at 1.5°C / min and hold for 90 min to complete dewaxing. Subsequently, heat the compact to 1180°C at 4°C / min and hold for 18 min. Then heat it to 1280°C at 2°C / min and hold for 10 min. Finally, heat the compact to 1380°C at 3°C / min and hold for 42 min to complete liquid phase sintering. After the sintering and holding period, switch to 5 MPa argon gas and hold for 12 min. Then cool the compact to 1250°C at 4°C / min and cool it with the furnace to obtain a high-strength, impact-resistant cemented carbide cold heading die.

[0059] Example 5:

[0060] Step 1: Add 750 mL of anhydrous ethanol and 110 mL of deionized water to a reaction vessel, add 95 g of tungsten carbide nanoparticles, disperse under ultrasonic conditions at 40 kHz for 25 min, and then mechanically stir at 450 rpm at 37 °C to form a uniform slurry. Separately, dissolve 115 g of cobalt nitrate hexahydrate in 125 mL of deionized water to obtain the first-stage cobalt salt solution. Add 52 g of oxalic acid dihydrate to 410 mL of deionized water and stir in a water bath at 45 °C until completely clear to obtain the first-stage oxalic acid solution. First, add the first-stage cobalt salt solution over 10 min, and then add the first-stage oxalic acid solution dropwise over 35 min. After the addition is complete, continue stirring at 37 °C for 45 min.

[0061] Step 2: Add 100 mL of anhydrous ethanol to another container, add 2 g of vanadium carbide, disperse under 40 kHz ultrasonic conditions for 10 min, and then slowly add it to the slurry obtained in Step 1. Continue stirring for 20 min. Then add 190 g of tungsten carbide micro powder, and dissolve 42 g of cobalt nitrate hexahydrate in 52 mL of deionized water to obtain the second-stage cobalt salt solution. Add 19 g of oxalic acid dihydrate to 155 mL of deionized water and stir in a 45 °C water bath until completely clear to obtain the second-stage oxalic acid solution. Implement the second-stage coating by adding the second-stage cobalt salt solution first and then the second-stage oxalic acid solution. After all the additions are completed, continue stirring for 42 min.

[0062] Step 3: The slurry obtained in Step 2 was concentrated under reduced pressure at 57℃ and 0.07MPa. Every 20 minutes, 5g of slurry samples were taken and dried in an oven at 105℃ until constant weight. The solid content was calculated as the percentage of dry weight to the total sample weight. When the solid content reached 51wt%, 2g of cerium nitrate hexahydrate was dissolved in 22mL of deionized water and added dropwise to the slurry over 10 minutes. After the addition was completed, stirring was continued for 20 minutes. Then, the slurry was concentrated under reduced pressure until the solid content reached 59wt%. 1g of cerium oxide nanopowder and 2g of polyethylene glycol 600 were added to 55mL of anhydrous ethanol and dispersed under ultrasonic conditions at 40kHz for 10 minutes. The mixture was then added to the slurry and stirred for another 18 minutes.

[0063] Step 4: Spread the wet material obtained in Step 3 evenly in a PTFE tray, vacuum dry at 85℃ for 14 hours, then break it up and pass it through a 40-mesh sieve. Load the resulting powder into a quartz boat and place it in a tube furnace. First, purge the atmosphere with high-purity argon gas for 30 minutes, then raise the temperature to 260℃ at 2.5℃ / min and hold for 70 minutes. Next, switch to high-purity hydrogen gas, raise the temperature to 360℃ at 3.5℃ / min and hold for 70 minutes, then reduce the temperature at 2℃ / min... The temperature was raised to 460℃ and held for 140 minutes. After cooling to room temperature, the powder was taken out under high-purity argon protection. 1g of graphite powder, 4g of polyethylene glycol 600, 5g of paraffin wax and 180mL of anhydrous ethanol were added to the reduced powder. The powder was wet-milled in a cemented carbide ball mill jar and cemented carbide balls at a ball-to-material mass ratio of 4:1 at 160rpm for 4 hours. After pouring out, the powder was vacuum-dried at 65℃ for 10 hours, dispersed and passed through a 60-mesh sieve to obtain the outer working area powder.

[0064] Step 5: Add 610g of tungsten carbide micro powder, 72g of cobalt powder, 1g of graphite powder, 5g of polyethylene glycol 600, 7g of paraffin wax and 310mL of anhydrous ethanol to a cemented carbide ball milling jar. Wet ball mill at 190rpm for 9h under the condition that the mass ratio of cemented carbide balls to powder is 5:1. After pouring out, vacuum dry at 65℃ for 12h, disperse and pass through a 60-mesh sieve to obtain the core carrier powder.

[0065] Step 6: Use the core rod mold to partition the mold. First, evenly spread 320g of outer working area powder around the core rod and the corresponding future mold lip and working zone. After compacting for 25s, pre-press at 70MPa. Then add 676g of core bearing powder, and finally press at 230MPa for 70s to obtain the pre-molded cavity blank.

[0066] Step 7: Place the compact obtained in Step 6 in a vacuum sintering furnace. Under a vacuum degree not exceeding 10 Pa, heat the compact to 290°C at 1.2°C / min and hold for 70 min. Then heat the compact to 470°C at 1.8°C / min and hold for 100 min to complete dewaxing. Subsequently, heat the compact to 1190°C at 4°C / min and hold for 25 min. Then heat the compact to 1290°C at 2°C / min and hold for 12 min. Finally, heat the compact to 1390°C at 3°C / min and hold for 50 min to complete liquid phase sintering. After the sintering and holding period, switch to 6 MPa argon gas and hold for 20 min. Then cool the compact to 1270°C at 5°C / min and cool it with the furnace to obtain a high-strength, impact-resistant cemented carbide cold heading die.

[0067] Comparative Example 1:

[0068] The difference from Example 1 is that the two-stage coating is not performed in steps one and two. Instead, 90g of tungsten carbide nanopowder, 180g of tungsten carbide micropowder, and 2g of vanadium carbide are first dispersed in a mixed system of 700mL of anhydrous ethanol, 100mL of deionized water, and 80mL of anhydrous ethanol. Then, 150g of cobalt nitrate hexahydrate is dissolved in 170mL of deionized water to obtain a cobalt salt solution, and 68g of oxalic acid dihydrate is dissolved in 550mL of deionized water to obtain an oxalic acid solution. The cobalt salt solution is added first, followed by the oxalic acid solution, and the coating of the cobalt-containing precursor is completed in one step. The remaining conditions are the same as in Example 1.

[0069] Comparative Example 2:

[0070] The difference from Example 1 is that 2g of vanadium carbide is not added in step two. Instead, 2g of tungsten carbide micro powder is added to 80mL of anhydrous ethanol and ultrasonically dispersed for 10min before being added to make up the total amount of solids and keep the amount of added liquid consistent. The other conditions are the same as in Example 1.

[0071] Comparative Example 3:

[0072] The difference from Example 1 is that 2g of vanadium carbide is still used in step two, but it is not added after the first stage of coating and before the second stage of coating. Instead, it is added at the same time as 1g of graphite powder, 3g of polyethylene glycol 600, 4g of paraffin and 150mL of anhydrous ethanol after the reduction treatment in step four is completed and cooled to room temperature. The other conditions are the same as in Example 1.

[0073] Comparative Example 4:

[0074] The difference from Example 1 is that when the solid content reaches 50wt% in step 3, 2g of cerium nitrate hexahydrate is not added. Instead, 2g of tungsten carbide micro powder is dispersed in 20mL of deionized water and added within 10min to make up the total amount of solid and keep the added liquid volume consistent. The other conditions are the same as in Example 1.

[0075] Comparative Example 5:

[0076] The difference from Example 1 is that when the solid content reaches 58wt% in step 3, instead of adding 1g of cerium oxide nanopowder, 1g of tungsten carbide micropowder and 2g of polyethylene glycol 600 are added to 50mL of anhydrous ethanol and ultrasonically dispersed for 10min before being added to make up the total amount of solids and keep the added liquid volume consistent. The other conditions are the same as in Example 1.

[0077] Comparative Example 6:

[0078] The difference from Example 1 is that in step three, 2g of cerium nitrate hexahydrate, 1g of cerium oxide nanopowder and 2g of polyethylene glycol 600 are not added in portions according to the solid content threshold, but are added all at once after step two and before the start of vacuum concentration. The other conditions are the same as in Example 1.

[0079] Comparative Example 7:

[0080] The difference from Example 1 is that: in step six, the partitioned molding is not performed. Instead, 305g of outer working area powder and 691g of core bearing powder are pre-mixed and molded at once, and directly pressed at 220MPa for 60s to form the shape. The other conditions are the same as in Example 1.

[0081] Performance testing:

[0082] Using the powders obtained in Examples 1-5 and Comparative Examples 1-7, blanks with dimensions of 45mm × 12mm × 8mm were simultaneously prepared while the actual cold heading molds were being made, and sintered in the same furnace as the molds. After sintering, samples were machined into the required standard sizes using wire electrical discharge machining and precision grinding. The final surface roughness of all samples was controlled to Ra ≤ 0.2μm, and the edges were uniformly chamfered to 0.1mm × 45°. Before testing, the samples were ultrasonically cleaned with anhydrous ethanol for 10 minutes and dried at 60℃ for 30 minutes. The cold heading application tests directly used the finished molds prepared in the corresponding examples or comparative examples, and the mold installation position, equipment parameters, lubrication conditions, and source of the processed wire were kept consistent within the same batch of tests.

[0083] The average grain size of tungsten carbide was determined according to GB / T 3488.2-2018 "Metallographic determination of microstructure of cemented carbide - Part 2: Measurement of WC grain size". One sample each from the lip region and the core region of each group of samples was prepared and polished before observation using a field emission scanning electron microscope in backscatter mode. The magnification was uniformly set to 5000x. The tungsten carbide grain size was statistically analyzed using the line cut-off method, with no less than 10 fields of view per sample and a total of no less than 400 cut-off points. The average grain size of the lip region and the core region were calculated separately.

[0084] Rockwell hardness: Tested according to GB / T 3849.1-2015 "Hard Alloy Rockwell Hardness Test (A Scale) Part 1: Test Method". Three specimens with ground surfaces were taken for each group of samples. A diamond cone indenter was used on the hardness tester with a pre-test force of 98.07 N and a total test force of 588.4 N. After applying the total test force, the load was held for 5 seconds before reading the value. Five points were measured on each specimen. The distance between any two indentation centers was not less than 3 mm, and the distance from the indentation center to the edge was not less than 2.5 mm. The average value of the 15 measuring points was taken as the hardness result for that group of samples.

[0085] Transverse fracture strength: Tested according to GB / T 3851-2015 "Determination of transverse fracture strength of cemented carbide". Five type B specimens were processed for each group of samples, with uniform dimensions of 20mm×6.5mm×5.25mm. The long side of the specimen was aligned with the pressing direction, and the support span was uniformly 14.5mm. The three-point bending method was used for testing, and the loading speed was controlled at 0.2mm / min. The fracture load of each specimen was recorded, and the transverse fracture strength was calculated according to the standard formula.

[0086] Room temperature impact toughness: Tested according to GB / T 1817-2017 "Test Method for Room Temperature Impact Toughness of Hard Alloys". Five unnotched specimens were processed for each group of samples, with uniform dimensions of 10mm×10mm×55mm. The test environment temperature was controlled at 23℃±2℃, and a pendulum impact testing machine was used. The initial energy of the pendulum was uniformly set to 150J. The absorbed energy was recorded after the specimen fractured, and the room temperature impact toughness result was obtained by dividing the absorbed energy by the fracture cross-sectional area.

[0087] Barcol toughness: Tested according to GB / T 33819-2017 "Barcol Toughness Test of Hard Alloys". Three polished specimens, approximately 10mm × 10mm × 6mm in size, were taken from each sample group. A Vickers indenter was used to apply a load of 980.7 N for 15 seconds. Five indentations were made on each specimen. The distance between the centers of the indentations was not less than three times the diagonal length of the indentation, and the distance from the center of the indentation to the edge of the specimen was not less than 2.5 times the diagonal length of the indentation. The Palmqvist crack lengths generated at the four corners of each indentation were measured using a 500x metallographic microscope, and the Barcol toughness was calculated using the standard formula, in N / mm.

[0088] Cold heading actual service life test: A multi-station cold heading machine of the same model was used for actual service evaluation. The processed material was wire rod from the same batch conforming to GB / T 6478-2015 "Steel for Cold Heading and Cold Extrusion," and was used after undergoing the same spheroidizing annealing, phosphating, saponification, and straightening treatments. The products were uniformly selected as M10×40 hexagonal head bolts conforming to GB / T 5782-2025 "Fasteners Hexagonal Head Bolts," and the cold heading speed was uniformly controlled at 120 pieces / min. The molds obtained in Examples 1-5 and Comparative Examples 1-7 were installed in the same station for testing. The machine was stopped every 2000 pieces produced. The die lip chipping width, working zone wear width, and radial crack length were inspected using a 50x stereomicroscope. Simultaneously, 100 consecutive bolts were randomly selected for dimensional and appearance acceptance according to GB / T 90.1-2023, and mechanical properties were sampled and verified according to GB / T 3098.1-2010. The lifespan is defined as any one of the following three conditions: the first occurrence of a chipped lip width greater than 0.10 mm, or a visible radial crack length greater than 0.20 mm, or a dimensional pass rate of less than 99.5% for 100 consecutive pieces. The cumulative number of qualified parts is used as the mold lifespan result.

[0089] The test results are shown in Table 1.

[0090] Table 1 Performance Test Results

[0091] sample Average grain size (μm) of WC in the lip region Average grain size (μm) in the core region (WC) Rockwell hardness Transverse fracture strength (MPa) <![CDATA[Charpy impact toughness at room temperature (kJ / m 2 )]]> Barcol toughness (N / mm) <![CDATA[Mold life (×10 3 pieces)]]> Lip chipping width (mm) Radial crack length (mm) 100 consecutive pieces dimensional pass rate (%) Example 1 0.82 1.34 89.4 4048 88.7 2360 1178 0.11 0.21 100 Example 2 0.88 1.29 89.6 3892 82.4 2280 1056 0.12 0.22 100 Example 3 0.74 1.36 89.5 4226 95.6 2480 1334 0.11 0.21 100 Example 4 0.85 1.33 89.3 3956 86.8 2325 1136 0.12 0.21 100 Example 5 0.89 1.44 89.1 4008 92.0 2405 1258 0.11 0.21 100 Comparative Example 1 1.12 1.38 88.6 3416 70.6 2085 742 0.09 0.19 99 Comparative Example 2 1.26 1.46 88.3 3474 72.4 2140 698 0.12 0.18 99 Comparative Example 3 1.08 1.4 88.7 3598 74.9 2185 782 0.11 0.22 100 Comparative Example 4 0.97 1.37 89.0 3678 78.5 2215 818 0.10 0.21 100 Comparative Example 5 1.01 1.39 88.8 3714 77.8 2195 878 0.11 0.21 100 Comparative Example 6 1.05 1.42 88.7 3556 76.0 2170 758 0.09 0.20 99 Comparative Example 7 1.17 1.21 89.1 3818 84.2 2290 842 0.10 0.18 99

[0092] As shown in Table 1, the cemented carbide cold heading dies prepared in Examples 1-5 generally achieved a good balance of strength and toughness, with Example 3 exhibiting the best overall performance. Compared to Example 1, although Example 2 achieved a Rockwell hardness of 89.6 HRA due to its relatively low cobalt content and milder sintering process, its average WC grain size in the lip region increased to 0.88 μm due to the lower amounts of VC, ionic cerium source, and particulate cerium source. Consequently, its transverse fracture strength, room temperature impact toughness, and die life decreased to 3892 MPa, 82.4 kJ / m², and so on. 2The 1,056,000 pieces demonstrate that simply pursuing high hardness cannot simultaneously achieve optimal service life. With the enhanced synergistic effect of two-stage cobalt-containing precursor coating, intercalated VC addition, and segmented introduction of two types of cerium sources, the average grain size of WC in the lip region of Example 3 was refined to 0.74 μm, and the transverse fracture strength, room temperature impact toughness, and Barcol toughness reached 4226 MPa, 95.6 kJ / m², and 2480 N / mm, respectively. The mold life increased to 1,334,000 pieces, indicating that by simultaneously improving the uniformity of cobalt phase distribution, interface purification effect, and grain boundary pinning ability, the resistance to crack initiation and propagation can be significantly improved while maintaining a high hardness level of 89.5 HRA. Although Example 5 maintained high impact toughness, due to the high sintering temperature and holding time, the WC grains in the lip region and core region increased to 0.89 μm and 1.44 μm, respectively, resulting in a decrease in hardness to 89.1 HRA and an overall lifespan lower than Example 3. This indicates that the performance improvement of this application does not increase monotonically with the amount added or the sintering strength, but rather there is an optimal window.

[0093] The results of Comparative Examples 1-6 show that the cancellation or misalignment of any key step leads to grain coarsening in the lip region, a decrease in transverse fracture strength, or a shortened actual lifespan. Specifically, Comparative Examples 1 and 2, due to the single coating of the cobalt precursor and the lack of VC crystal suppression, had mold lives of only 742,000 and 698,000 pieces, respectively. Comparative Example 7, in particular, although its static mechanical properties remained at a high level after mixed molding, exhibited Rockwell hardness, transverse fracture strength, and room temperature impact toughness of 89.1 HRA, 3818 MPa, and 84.2 kJ / m, respectively. 2 However, due to the failure of the outer working area reinforcement organization to be oriented to the lip and working zone area, the mold life still dropped to 842,000 pieces, and the dimensional qualification rate of 100 consecutive pieces dropped to 99.0%, which further proves that this application is not a single component modification or a single process optimization, but a multi-level design that achieves a synergistic improvement in strength, impact resistance and actual cold heading life, demonstrating a comprehensive effect of 1+1 greater than 2.

[0094] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a high-strength, impact-resistant cemented carbide cold heading die, characterized in that, Includes the following steps: S1. Preparation of outer working zone powder: Tungsten carbide nanoparticles are dispersed and coated with a cobalt-containing precursor in the first stage, followed by the addition of vanadium carbide and tungsten carbide microparticles for a second stage of cobalt-containing precursor coating; when the slurry solid content reaches 48wt%-52wt%, an ionic cerium source is added, and when the slurry solid content reaches 56wt%-60wt%, a particulate cerium source and a portion of polyethylene glycol 600 are added; subsequently, the slurry is concentrated under reduced pressure, dried, reduced, and ball-milled to obtain the outer working zone powder; the remaining polyethylene glycol 600, graphite powder, and paraffin are added during the ball milling process; S2. Preparation of core support area powder: Tungsten carbide micro powder and cobalt powder are mixed and ball-milled to obtain core support area powder; S3. Partitioned molding and pressing: Using a core rod mold, the outer working area powder is first laid around the core rod and in the corresponding parts of the mold lip and working belt after molding and pre-pressed. Then, the core bearing area powder is added for final pressing to obtain the pressed blank. S4. Sintering: The pressed blank is dewaxed, liquid phase sintered and argon pressure sintering is performed to obtain a high-strength, impact-resistant cemented carbide cold heading die; The resulting high-strength, impact-resistant cemented carbide cold heading die includes an outer working area and a core bearing area. The outer working area surrounds the mold cavity of the cold heading die and is located in the area corresponding to the mold lip and the working zone. The core bearing area is located on the side of the outer working area away from the mold cavity, and the outer working area and the core bearing area are sintered and integrally formed.

2. The method for preparing a high-strength, impact-resistant cemented carbide cold heading die according to claim 1, characterized in that, In step S1, the raw materials for preparing the outer working area powder, by mass parts, include: 80-100 parts tungsten carbide nanopowder, 100-120 parts first-stage cobalt source, 160-200 parts tungsten carbide micropowder, 35-45 parts second-stage cobalt source, 1-3 parts vanadium carbide, 1-3 parts ionic cerium source, 0.5-1.5 parts particulate cerium source, 3-7 parts polyethylene glycol 600, 1 part graphite powder, and 3-5 parts paraffin wax; in step S2, the raw materials for preparing the core bearing area powder, by mass parts, include: 600-640 parts tungsten carbide micropowder and 65-75 parts cobalt powder.

3. The method for preparing a high-strength, impact-resistant cemented carbide cold heading die according to claim 1 or 2, characterized in that, Both the first-stage cobalt source and the second-stage cobalt source are cobalt nitrate hexahydrate, the ionic cerium source is cerium nitrate hexahydrate, and the particulate cerium source is cerium oxide nanoparticles.

4. The method for preparing a high-strength, impact-resistant cemented carbide cold heading die according to claim 1 or 2, characterized in that, The first-stage cobalt-containing precursor is formed by reacting 100-120 parts of the first-stage cobalt source with 46-54 parts of oxalate dihydrate, and the second-stage cobalt-containing precursor is formed by reacting 35-45 parts of the second-stage cobalt source with 16-20 parts of oxalate dihydrate.

5. The method for preparing a high-strength, impact-resistant cemented carbide cold heading die according to claim 1 or 2, characterized in that, The tungsten carbide nanopowder has a particle size of 150nm-200nm, the tungsten carbide micro powder has a particle size of 2μm, the cobalt powder has a particle size of 2μm, the vanadium carbide has a particle size of less than 2μm, the cerium oxide nanopowder has a particle size of less than 50nm, and the graphite powder has a particle size of less than 20μm.

6. The method for preparing a high-strength, impact-resistant cemented carbide cold heading die according to claim 1, characterized in that, In step S1, the reduction is as follows: first, argon gas is introduced and the temperature is increased to 245-260℃ at 2-2.5℃ / min, and held for 50-70min; then, hydrogen gas is switched, the temperature is increased to 345-360℃ at 3-3.5℃ / min and held for 50-70min, then the temperature is increased to 445-460℃ at 2℃ / min and held for 110-140min, and then cooled to room temperature before being taken out.

7. The method for preparing a high-strength, impact-resistant cemented carbide cold heading die according to claim 1, characterized in that, In step S1, ball milling is performed at a ball-to-material mass ratio of 4:1, using a wet ball milling method at 145-160 rpm for 2.5-4 hours; in step S2, ball milling is performed at a ball-to-material mass ratio of 5:1, using a wet ball milling method at 175-190 rpm for 7-9 hours.

8. The method for preparing a high-strength, impact-resistant cemented carbide cold heading die according to claim 1, characterized in that, In step S3, the outer working area powder is first evenly spread around the core rod and the parts corresponding to the mold lip and working belt after molding. After vibration for 18-25s, it is pre-pressed at 55-70MPa. Then, the core bearing area powder is added, and the final pressure is 215-230MPa and held for 60-70s to obtain the pressed blank.

9. The method for preparing a high-strength, impact-resistant cemented carbide cold heading die according to claim 1, characterized in that, In step S4, the compact is placed in a vacuum sintering furnace. Under a vacuum degree not exceeding 10 Pa, the temperature is increased to 275-290℃ at 0.9-1.2℃ / min and held for 55-70 min. Then, the temperature is increased to 440-470℃ at 1.4-1.8℃ / min and held for 85-100 min for dewaxing. Subsequently, the temperature is increased to 1175-1190℃ at 4℃ / min and held for 18-25 min. Then, the temperature is increased to 1275-1290℃ at 2℃ / min and held for 10-12 min. Finally, the temperature is increased to 1375-1390℃ at 3℃ / min and held for 42-50 min to complete liquid phase sintering. The pressure is then switched to 4-6 MPa argon gas for 12-20 min, and then the temperature is reduced to 1240-1270℃ at 4-5℃ / min and cooled with the furnace.

10. The method for preparing a high-strength, impact-resistant cemented carbide cold heading die according to claim 1, characterized in that, In step S1, the first stage cobalt source solution is first added to the tungsten carbide nanopowder slurry, and then the first stage oxalic acid solution prepared by oxalic acid dihydrate is added to coat the first stage cobalt-containing precursor. After completing the first stage of cobalt-containing precursor coating, vanadium carbide is added first, followed by tungsten carbide micro powder. The second stage of cobalt-containing precursor coating is then carried out in the order of adding the second stage cobalt source solution first, followed by the second stage oxalic acid solution prepared by oxalic acid dihydrate.