Method for precisely controlling carbon content of bonding phase of gt35 steel-bonded carbide

Abstract

The application discloses a method for precisely controlling carbon content of a GT35 steel-bonded hard alloy bonding phase, and relates to the technical field of powder metallurgy, which comprises the following steps: Ti-Cr-Mo-C composite hard phase components, Fe powder and carbon supplementing agents are weighed according to a mass ratio of (32-38):(61.7-67.9):(0.1-0.3), and are uniformly mixed by using a dry mixing or low-oxygen medium ball milling method to obtain mixed powder, wherein Ti, Cr, Mo and C in the Ti-Cr-Mo-C composite hard phase components exist at least partially in the form of carbides or solid solution carbides; the mixed powder is pressed and formed to obtain a compact; the compact is sequentially subjected to solid phase sintering and liquid phase sintering to obtain a sintered body; and the sintered body is subjected to heat treatment to obtain a GT35 steel-bonded hard alloy. The GT35 steel-bonded hard alloy prepared by the method can significantly reduce carbon content fluctuation and improve the uniformity of the structure and the consistency of the hardness.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, and in particular relates to a method for precisely controlling the carbon content of the binder phase in GT35 steel-bonded cemented carbide. Background Technology

[0002] The typical composition of GT35 steel-bonded cemented carbide is approximately 35 wt% TiC hard phase and the remaining Cr-Mo low-alloy steel binder phase. The carbon content of the binder phase needs to be precisely controlled within the range of 0.4~0.6 wt% to achieve a martensitic matrix hardness of 58~64 HRC after quenching, while also considering wear resistance, toughness, and service life. This alloy is widely used in precision molds, guide wheels, high-speed wire drawing dies, and other applications requiring high performance consistency.

[0003] The existing preparation process of GT35 steel-bonded cemented carbide usually adopts the powder metallurgy route: using pure TiC powder (about 35wt%), Fe powder, Cr powder, Mo powder and carbon black as raw materials, the finished product is obtained by wet grinding and mixing, drying, pressing and molding, sintering and heat treatment.

[0004] However, the current process has the following main technical problems: 1. The amount of carbon black added in the later stage is relatively large, and it is easily affected by oxygen to generate CO during wet milling, resulting in large fluctuations in carbon loss (the carbon content between batches often fluctuates by ±0.15~0.25 wt% or more).

[0005] 2. Fluctuations in carbon content directly lead to uneven carbon solubility in the binder phase martensite, resulting in significant differences in hardness after quenching, local decarburization or carburization zones, and poor microstructure uniformity.

[0006] 3. The problem of carbon loss due to oxygenation in wet grinding is difficult to completely avoid. Even if low-oxygen media or dry grinding are used, the complexity and cost of the process will increase, and the batch stability is still not ideal.

[0007] Therefore, there is an urgent need for an effective method to regulate carbon behavior, so as to significantly reduce the amount of carbon supplementer used in the later stage, avoid the problem of carbon loss in wet milling, and achieve precise control of carbon content in the binder phase. Summary of the Invention

[0008] To solve the above-mentioned technical problems, the present invention provides a method for precisely controlling the carbon content of the binder phase in GT35 steel-bonded cemented carbide, the specific technical solution of which is as follows: A method for precisely controlling the carbon content of the binder phase in GT35 steel cemented carbide bonding phase includes the following steps: S1. Weigh the Ti-Cr-Mo-C composite hard phase component, Fe powder and carbon supplement in a mass ratio of (32~38):(61.7~67.9):(0.1~0.3), and mix them evenly by dry mixing or ball milling in a low-oxygen medium to obtain a mixed powder, wherein Ti, Cr, Mo and C in the Ti-Cr-Mo-C composite hard phase component exist at least partially in the form of carbides or solid solution carbides; S2. Press the mixed powder into a compact; S3. The pressed blank is subjected to solid-phase sintering and liquid-phase sintering in sequence to obtain a sintered body; S4. The sintered body is heat-treated to obtain GT35 steel-bonded cemented carbide.

[0009] Preferably, in the Ti-Cr-Mo-C composite hard phase component, the total mass content of Cr and Mo is 3~12 wt%, the mass ratio of the two is (1~2):1, the mass content of C is 1.5~3.5 wt%, and the balance is Ti.

[0010] Preferably, the Ti-Cr-Mo-C composite hard phase component is at least one of the following a or b: a)(Ti,Cr,Mo)C solid solution particles; b) Carbon-coated Ti-Cr-Mo-C composite particles, consisting of Ti-Cr-Mo-C composite core particles and a carbon residual layer covering them.

[0011] Preferably, the (Ti,Cr,Mo)C solid solution particles are prepared by at least one of the following methods c or d: c) Carbothermic reduction method: After mixing the oxide raw materials containing Ti, Cr and Mo with the carbon source, the carbothermic reduction reaction is carried out under high temperature inert or reducing atmosphere to generate solid solution particles. d) Mechanical alloying method: Ti source, Cr source, Mo source and carbon source powders are subjected to high-energy ball milling alloying treatment to form solid solution particles.

[0012] Preferably: In the carbothermic reduction method, the oxide raw materials containing Ti, Cr, and Mo are selected from TiO2, Cr2O3, and MoO3, and the carbon source is selected from at least one of carbon black, activated carbon, and graphite powder. The carbothermic reduction reaction temperature is 1300~1800℃, and the temperature is maintained for 1~4 h. In the mechanical alloying method, the Ti source is selected from Ti powder, the Cr source is selected from Cr powder, the Mo source is selected from Mo powder, and the carbon source is selected from at least one of carbon black and graphite powder. The high-energy ball milling alloying treatment uses a planetary ball mill or a vibratory ball mill with a rotation speed of 300~600 rpm, a ball-to-material mass ratio of (8~20):1, and a ball milling time of 10~50 h.

[0013] Preferably, the carbon-coated Ti-Cr-Mo-C composite particles are prepared by at least one of the following methods e and f: e) After mixing and coating the Ti-Cr-Mo-C composite core particles with the organic carbon precursor solution, the mixture is subjected to low-temperature carbonization treatment to allow the organic precursor to pyrolyze and form a carbon residue layer. f) The Ti-Cr-Mo-C composite core particles are mixed with a metal-organic compound solution, and a metal-organic composite layer is formed in situ on the particle surface by solvothermal or vapor deposition. Then, a low-temperature pyrolysis carbonization treatment is performed to transform the metal-organic composite layer into a metal-doped carbon residue layer.

[0014] Preferably, in method e: The organic carbon precursor is selected from at least one of phenolic resin, polyvinyl alcohol, furfural resin, glucose, and polyacrylonitrile; The solvent for the solution is selected from at least one of ethanol, water, and acetone; The mass ratio of Ti-Cr-Mo-C composite core particles to organic carbon precursor solution is (5~20):1; Low-temperature carbonization is carried out under inert atmosphere or vacuum conditions, with a carbonization temperature of 400~700℃, a holding time of 0.5~5h, and a heating rate of 2~10℃ / min.

[0015] Preferably, in method f: The organometallic compound is selected from at least one of titanates, molybdates, organochromium compounds, and metal acetylacetonates; The solution solvent is selected from at least one of ethanol, isopropanol, N,N-dimethylformamide, dimethyl sulfoxide, and water; The mass ratio of Ti-Cr-Mo-C composite core particles to organometallic compound solution is (5~25):1; The solvothermal and vapor phase deposition processes were carried out in a closed container and a vapor phase reactor, respectively. The solvothermal reaction temperature was 120~250℃ and the holding time was 2~24 h. The vapor phase deposition temperature was 200~500℃ and the deposition time was 0.5~8 h. The low-temperature pyrolysis carbonization treatment is carried out under an inert atmosphere or vacuum, with a carbonization temperature of 500~900℃, a holding time of 0.5~6 h, and a heating rate of 2~15℃ / min.

[0016] Preferably, in step S3: Solid-state sintering is carried out under vacuum or slightly positive pressure inert atmosphere, with a sintering temperature of 1000~1250℃, a holding time of 0.5~3h, and a heating rate of 3~15℃ / min. Liquid phase sintering is carried out under vacuum or slightly positive pressure inert atmosphere, with a sintering temperature of 1350~1480℃, a holding time of 1~4 h, and a heating rate of 2~10℃ / min.

[0017] Preferably: In step S2, the pressing molding adopts unidirectional or isostatic pressing, the pressing pressure is 200~600 MPa, and the holding time is 5~60 s; In step S4, the heat treatment includes quenching and tempering. Quenching is performed by oil quenching or salt bath quenching at a temperature of 800~950℃, holding for 0.2~1 h and then rapidly cooling. Tempering is performed in air or a protective atmosphere at a temperature of 150~350℃ and holding for 1~4 h.

[0018] The present invention has the following beneficial effects: 1. Significantly reduce carbon content fluctuations: By controlling carbon behavior from the source through Ti-Cr-Mo-C composite hard phase components, the amount of carbon supplementing agent used in the later stage is reduced and carbon loss during wet milling is avoided.

[0019] 2. Improved microstructure uniformity and hardness consistency: Narrow control of carbon content makes the martensite carbon solubility more uniform, and the hardness fluctuation after quenching can be significantly reduced.

[0020] 3. Reduce porosity: Cr / Mo solid solution improves the wettability of TiC with steel substrate, and combined with segmented sintering process, it can effectively reduce the porosity of the alloy. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below. The description in this part is only exemplary and explanatory, and should not be used to limit the scope of protection of the present invention in any way.

[0022] This embodiment provides a method for precisely controlling the carbon content of the binder phase in GT35 steel cemented carbide, comprising the following steps: S1. Weigh the Ti-Cr-Mo-C composite hard phase component, Fe powder and carbon supplement at a mass ratio of (32~38):(61.7~67.9):(0.1~0.3), and mix them evenly by dry mixing or ball milling in a low-oxygen medium to obtain a mixed powder, wherein Ti, Cr, Mo and C in the Ti-Cr-Mo-C composite hard phase component exist at least partially in the form of carbides or solid solution carbides.

[0023] S2. Press the mixed powder into a compact.

[0024] S3. The compact is subjected to solid-phase sintering and liquid-phase sintering in sequence to obtain a sintered body.

[0025] S4. Heat-treat the sintered body to obtain GT35 steel-bonded cemented carbide.

[0026] Specifically, in the Ti-Cr-Mo-C composite hard phase component, Ti, Cr, Mo, and C exist at least partially in the form of carbides or solid-solution carbides. These carbides / solution carbides have high thermodynamic stability, and the solid-solution effect of Cr and Mo can "lock" in some carbon during sintering, inhibiting the drastic migration and loss of carbon. The mass ratio (32~38):(61.7~67.9):(0.1~0.3) ensures that the equivalent TiC content is stable at around 35 wt%, and the Cr / Mo / C are precisely distributed through the composite components, avoiding the component segregation caused by traditional multi-component powder mixing.

[0027] The composite hard phase component replaces the traditional 35 wt% pure TiC + partial Cr / Mo / C addition. The carbon source mainly comes from the solid-solid carbon inside the component and / or the surface carbon residue layer. During the solid-phase sintering stage (low temperature), carbon gradually diffuses / releases to compensate for the diffusion loss in the early stage; during the liquid-phase sintering stage (high temperature), the Cr / Mo solid solution further balances the carbon potential, achieving adaptive carbon replenishment and locking.

[0028] The carbon supplement is added in only trace amounts (0.1~0.3 wt%) as an initial carbon supplement, rather than the main carbon source, thus significantly reducing the dependence on subsequent carbon black. At the same time, the entire batching and mixing process adopts dry mixing or low-oxygen media ball milling, completely avoiding the carbon loss problem caused by CO generation due to oxygenation in traditional wet milling.

[0029] Through the above mechanism, this implementation method achieves the control of carbon behavior from the source of the hard phase, avoiding the main source of carbon fluctuations in traditional processes (carbon loss during wet grinding + instability due to large-scale carbon replenishment in the later stage).

[0030] Compared with the prior art, this embodiment has the following beneficial effects: 1. Significantly reduce carbon content fluctuations: By controlling carbon behavior from the source through Ti-Cr-Mo-C composite hard phase components, the amount of carbon supplementing agent used in the later stage is reduced and carbon loss during wet milling is avoided.

[0031] 2. Improved microstructure uniformity and hardness consistency: Narrow control of carbon content makes the martensite carbon solubility more uniform, and the hardness fluctuation after quenching can be significantly reduced.

[0032] 3. Reduce porosity: Cr / Mo solid solution improves the wettability of TiC with steel substrate, and combined with segmented sintering process, it can effectively reduce the porosity of the alloy.

[0033] Furthermore, in the Ti-Cr-Mo-C composite hard phase component, the total mass content of Cr and Mo is 3~12 wt%, the mass ratio of the two is (1~2):1, the mass content of C is 1.5~3.5 wt%, and the balance is Ti.

[0034] Specifically, the above range ensures that the composite components form an appropriate amount of (Ti,Cr,Mo)C solid solution or composite carbide phase during sintering. The solid solution of Cr and Mo improves the thermodynamic stability of the carbides and inhibits the free diffusion and loss of carbon; the C content range provides sufficient dissolved carbon and a releaseable carbon source, compensating for diffusion losses in the solid phase and synergistically maintaining carbon potential balance with the Cr / Mo solid solution in the liquid phase. A ratio of (1~2):1 is beneficial for improving wettability and oxidation resistance when Cr is slightly higher or equal in amount, while avoiding the formation of a brittle phase due to excessive Mo.

[0035] The preferred total Cr+Mo content is 5-10 wt%, achieving the best balance between solid solution effect and carbon locking ability. If the Cr:Mo ratio is closer to 1:1, Mo solid solution is stronger, suitable for applications emphasizing wear resistance; when it is closer to 2:1, Cr solid solution is enhanced, suitable for applications emphasizing corrosion resistance or oxidation resistance. The C content is in the range of 1.5-3.5 wt%, which can be finely adjusted according to the type of composite components.

[0036] Beneficially, compared with traditional post-carbonization processes, this elemental range makes the composite hard phase component the main carrier for carbon regulation, reducing dependence on carbonization agents, effectively reducing carbon fluctuations, and avoiding the problems of solid solution weakening due to insufficient Cr / Mo or microstructure embrittlement due to excessive Cr / Mo.

[0037] Furthermore, the Ti-Cr-Mo-C composite hard phase component is at least one of the following a or b: a)(Ti,Cr,Mo)C solid solution particles.

[0038] b) Carbon-coated Ti-Cr-Mo-C composite particles, consisting of Ti-Cr-Mo-C composite core particles and a carbon residual layer covering them.

[0039] In this process, (Ti,Cr,Mo)C solid solution particles form a multi-component carbide solid solution through the solid solution of Cr and Mo into the TiC lattice, improving carbide stability, reducing the migration of free carbon, and buffering carbon potential fluctuations throughout the sintering process. The core particles of the carbon-coated Ti-Cr-Mo-C composite particles provide solid solution locking, while the residual carbon layer on the surface releases carbon through thermal decomposition during the solid-phase sintering stage (at lower temperatures), replenishing the carbon lost in the early diffusion stage. In the liquid phase stage, the remaining carbon works synergistically with the solid solution mechanism to achieve phased control of carbon through "replenishment followed by locking." Both forms can be used individually or in any combination (e.g., 70% a + 30% b) to adapt to application scenarios with different carbon fluctuation sensitivities.

[0040] Furthermore, the (Ti,Cr,Mo)C solid solution particles are prepared by at least one of the following methods c or d: c) Carbothermic reduction method: After mixing the oxide raw materials containing Ti, Cr and Mo with the carbon source, the carbothermic reduction reaction is carried out under high temperature inert or reducing atmosphere to generate solid solution particles.

[0041] d) Mechanical alloying method: Ti source, Cr source, Mo source and carbon source powders are subjected to high-energy ball milling alloying treatment to form solid solution particles.

[0042] Furthermore: In the carbothermic reduction method, the oxide raw materials containing Ti, Cr, and Mo are selected from TiO2, Cr2O3, and MoO3, and the carbon source is selected from at least one of carbon black, activated carbon, and graphite powder. The carbothermic reduction reaction temperature is 1300~1800℃, and the temperature is maintained for 1~4 h.

[0043] In the mechanical alloying method, the Ti source is selected from Ti powder, the Cr source is selected from Cr powder, the Mo source is selected from Mo powder, and the carbon source is selected from at least one of carbon black and graphite powder. The high-energy ball milling alloying treatment uses a planetary ball mill or a vibratory ball mill with a rotation speed of 300~600 rpm, a ball-to-material mass ratio of (8~20):1, and a ball milling time of 10~50 h.

[0044] In the carbothermic reduction method, the oxide raw materials and carbon source are simultaneously reduced and dissolved at high temperature to form uniform (Ti,Cr,Mo)C particles. Cr / Mo dissolves into the TiC lattice from the synthesis source, improving the carbon locking efficiency. The typical industrial parameters are a reaction temperature of 1300~1800℃ and a holding time of 1~4 h. The atmosphere can be an Ar / H2 mixture.

[0045] Mechanical alloying involves atomic-level mixing and non-equilibrium solid solution of elemental powders (Ti powder, Cr powder, Mo powder, and carbon source) through high-energy ball milling, forming fine-grained or nanoscale solid solution particles with high uniformity and shorter carbon diffusion paths. The milling speed is 300-600 rpm, the ball-to-powder ratio is (8-20):1, and the time is 10-50 h, which can be adjusted according to the equipment. Optimal settings of 400-500 rpm and 20-40 h are preferred for achieving the best solid solution uniformity. These two methods can be used in series (pre-alloying + post-treatment).

[0046] Furthermore, the carbon-coated Ti-Cr-Mo-C composite particles are prepared by at least one of the following methods e and f: e) After mixing and coating the Ti-Cr-Mo-C composite core particles with the organic carbon precursor solution, the mixture is subjected to low-temperature carbonization treatment to allow the organic precursor to pyrolyze and form a carbon residue layer.

[0047] f) The Ti-Cr-Mo-C composite core particles are mixed with a metal-organic compound solution, and a metal-organic composite layer is formed in situ on the particle surface by solvothermal or vapor deposition. Then, a low-temperature pyrolysis carbonization treatment is performed to transform the metal-organic composite layer into a metal-doped carbon residue layer.

[0048] Furthermore, in method e: The organic carbon precursor is selected from at least one of phenolic resin, polyvinyl alcohol, furfural resin, glucose, and polyacrylonitrile.

[0049] The solvent for the solution is selected from at least one of ethanol, water, and acetone.

[0050] The mass ratio of Ti-Cr-Mo-C composite core particles to organic carbon precursor solution is (5~20):1.

[0051] Low-temperature carbonization is carried out under inert atmosphere or vacuum conditions, with a carbonization temperature of 400~700℃, a holding time of 0.5~5h, and a heating rate of 2~10℃ / min.

[0052] Furthermore, in method f: The organometallic compound is selected from at least one of titanates, molybdates, organochromium compounds, and metal acetylacetone salts.

[0053] The solvent for the solution is selected from at least one of ethanol, isopropanol, N,N-dimethylformamide, dimethyl sulfoxide, and water.

[0054] The mass ratio of Ti-Cr-Mo-C composite core particles to organometallic compound solution is (5~25):1.

[0055] The solvothermal and vapor phase deposition processes were carried out in a closed container and a vapor phase reactor, respectively. The solvothermal reaction temperature was 120~250℃ and the holding time was 2~24 h. The vapor phase deposition temperature was 200~500℃ and the deposition time was 0.5~8 h.

[0056] The low-temperature pyrolysis carbonization treatment is carried out under an inert atmosphere or vacuum, with a carbonization temperature of 500~900℃, a holding time of 0.5~6 h, and a heating rate of 2~15℃ / min.

[0057] In method e, organic precursors (such as phenolic resin) form a uniform coating layer on the surface of the core particles. Low-temperature carbonization pyrolysis releases the amorphous carbon residue layer, providing carbon replenishment in the solid phase stage. In method f, organometallic compounds (such as titanate, chromium acetylacetone, etc.) form a metal-organic composite layer in situ. After pyrolysis, it is transformed into a metal-doped carbon residue layer (doped with Cr / Mo / Ti nanoparticles or carbides), which enhances the adhesion, conductivity and thermal stability of the carbon layer. During sintering, fine carbide particles are further generated in situ, synergistically locking carbon.

[0058] Furthermore, in step S3: Solid-state sintering is carried out under vacuum or slightly positive pressure inert atmosphere, with a sintering temperature of 1000~1250℃, a holding time of 0.5~3h, and a heating rate of 3~15℃ / min.

[0059] Liquid phase sintering is carried out under vacuum or slightly positive pressure inert atmosphere, with a sintering temperature of 1350~1480℃, a holding time of 1~4 h, and a heating rate of 2~10℃ / min.

[0060] Among them, solid-phase sintering promotes the initial diffusion and release of carbon, making up for the losses in the early stage; liquid-phase sintering achieves densification, and the Cr / Mo solid solution and carbon potential are finally balanced, avoiding excess or deficiency of carbon.

[0061] Furthermore: In step S2, the pressing molding adopts unidirectional or isostatic pressing, the pressing pressure is 200~600 MPa, and the holding time is 5~60 s.

[0062] In step S4, the heat treatment includes quenching and tempering. Quenching is performed by oil quenching or salt bath quenching at a temperature of 800~950℃, holding for 0.2~1 h, and then rapidly cooling. Tempering is carried out in air or a protective atmosphere at a temperature of 150~350℃, holding for 1~4 h.

[0063] High-pressure pressing yields high-density compacts; quenching forms martensite; and tempering releases stress and adjusts toughness.

[0064] Specific embodiments are provided below. These embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0065] Step 1: Preparation of Ti-Cr-Mo-C composite hard phase components Raw material weighing: TiO2 148.6 g, Cr2O3 11.4 g, MoO3 7.2 g, carbon black (purity ≥99%) 9.8 g. The above raw materials were placed in a planetary ball mill and ball-milled for 8 h (350 rpm) with zirconia balls (ball-to-material ratio 10:1) under Ar atmosphere to obtain a uniformly mixed powder.

[0066] The mixed powder was placed in a graphite crucible and placed in a high-temperature tube furnace. After purging oxygen with Ar gas (flow rate 80 mL / min) for 30 min, the temperature was increased to 1620℃ at 5℃ / min and held for 2.5 h to carry out the carbothermic reduction reaction.

[0067] After naturally cooling to room temperature, the product was removed, lightly ground with an agate mortar and passed through a 400-mesh sieve to obtain (Ti,Cr,Mo)C solid solution particles.

[0068] Step 2: Preparation of GT35 steel-bonded cemented carbide Ingredients: 35.0 g of Ti-Cr-Mo-C composite hard phase component, 64.8 g of pure iron powder (purity ≥99.5%), and 0.2 g of carbon black. The above components were placed in a planetary ball mill and dry-mixed under an Ar atmosphere (zirconia balls, ball-to-material ratio 8:1, rotation speed 380 rpm, time 18 h) to obtain a uniformly mixed powder.

[0069] The mixed powder is loaded into a unidirectional pressing mold with a diameter of 30 mm and pressed on a hydraulic press at a pressure of 420 MPa for 30 s to obtain a pressed blank.

[0070] The pressed blank is placed in a vacuum sintering furnace and evacuated to a vacuum level of 5×10. -3 After Pa, the temperature is increased to 1180℃ at 8℃ / min and held for 1.8 h; then increased to 1435℃ at 5℃ / min and held for 2.2 h; and then cooled to room temperature with the furnace.

[0071] The sintered body was placed in a box-type resistance furnace, heated to 880℃ and held for 35 min, then oil quenched; subsequently tempered in a muffle furnace at 180℃ for 2.5 h and air cooled.

[0072] Step 3: Performance Testing 1. Carbon content of the binder phase: The carbon content of the binder phase was calculated by subtracting the carbon content of the hard phase from the overall carbon content using a carbon-sulfur analyzer (combustion method). Each sample was measured twice and the average value was taken.

[0073] 2. Carbon content fluctuation range: 5 batches were prepared independently, and the average value ± standard deviation was calculated.

[0074] 3. Rockwell hardness (HRC): A hardness tester was used with a load of 150 kgf. Ten points were measured on each sample surface, and the average value was taken.

[0075] 4. Hardness fluctuation range: Statistical average of 5 batches ± standard deviation.

[0076] The test data is shown in Table 1 below: In Example 1, the average carbon content of the binder phase in the 5 batches was 0.499 wt%, with a fluctuation range of only ±0.020 wt%; the average hardness was 62.1 HRC, with a fluctuation of only ±0.6 HRC, indicating that the carbon content was stable and the hardness was highly consistent.

[0077] Example 2 Step 1: Preparation of Ti-Cr-Mo-C composite hard phase components Raw material weighing: 172.8 g Ti powder (purity ≥99.5%), 8.6 g Cr powder (purity ≥99%), 6.4 g Mo powder (purity ≥99%), and 4.2 g carbon black (purity ≥99%). The above raw materials were placed in a planetary ball mill and ball-milled at high energy in an Ar atmosphere using zirconia balls (ball-to-material ratio 12:1) (420 rpm, 32 h) to obtain Ti-Cr-Mo-C mechanical alloying precursor powder.

[0078] Take 180.0 g of mechanically alloyed precursor powder and place it in a beaker. Prepare a phenolic resin ethanol solution (phenolic resin: ethanol = 1:4 mass ratio, total solution volume 21.6 g). Pour the precursor powder into the solution and ultrasonically disperse for 30 min (ultrasonic cleaner, power 200 W, frequency 40 kHz), then mechanically stir for 2 h (speed 500 rpm). Place the slurry in a vacuum drying oven and vacuum dry at 60℃ for 6 h to obtain coated precursor particles.

[0079] The coated precursor particles were placed in a tube furnace, and after purging with Ar gas (flow rate 60 mL / min) for 20 min to remove oxygen, the temperature was increased to 550℃ at 4℃ / min and held for 2.0 h for low-temperature carbonization. After natural cooling to room temperature, the product was removed, lightly ground, and passed through a 400-mesh sieve to obtain carbon-coated Ti-Cr-Mo-C composite particles.

[0080] Step 2: Preparation of GT35 steel-bonded cemented carbide Ingredients: 34.0 g of carbon-coated Ti-Cr-Mo-C composite particles, 65.7 g of pure iron powder (purity ≥99.5%), and 0.3 g of carbon black. The above components were placed in a planetary ball mill and dry-mixed under an Ar atmosphere (zirconia balls, ball-to-material ratio 8:1, rotation speed 380 rpm, time 18 h) to obtain a uniformly mixed powder.

[0081] The mixed powder is loaded into a unidirectional pressing mold with a diameter of 30 mm and pressed on a hydraulic press at a pressure of 420 MPa for 30 s to obtain a pressed blank.

[0082] The pressed blank is placed in a vacuum sintering furnace and evacuated to a vacuum level of 5×10. -3 After Pa, the temperature is increased to 1180℃ at 8℃ / min and held for 1.8 h; then increased to 1435℃ at 5℃ / min and held for 2.2 h; and then cooled to room temperature with the furnace.

[0083] The sintered body was placed in a box-type resistance furnace, heated to 880℃ and held for 35 min, then oil quenched; subsequently tempered in a muffle furnace at 180℃ for 2.5 h and air cooled.

[0084] Step 3: Performance Testing 1. Carbon content of the binder phase: The carbon content of the binder phase was calculated by subtracting the carbon content of the hard phase from the overall carbon content using a carbon-sulfur analyzer (combustion method). Each sample was measured twice and the average value was taken.

[0085] 2. Carbon content fluctuation range: 5 batches were prepared independently, and the average value ± standard deviation was calculated.

[0086] 3. Rockwell hardness (HRC): A hardness tester was used with a load of 150 kgf. Ten points were measured on each sample surface, and the average value was taken.

[0087] 4. Hardness fluctuation range: Statistical average of 5 batches ± standard deviation.

[0088] The test data is shown in Table 2 below: Example 2 uses carbon-coated Ti-Cr-Mo-C composite particles. The average carbon content of the binder phase in 5 batches was 0.496 wt%, with a fluctuation range of only ±0.013 wt%, which is further reduced compared to Example 1. The average hardness was 62.3 HRC, with a fluctuation of only ±0.5 HRC. This indicates that the staged release mechanism of the carbon residue layer on the surface further improved the batch stability of carbon content and further improved the consistency of hardness.

[0089] Example 3 Step 1: Preparation of Ti-Cr-Mo-C composite hard phase components Raw material weighing: 171.2 g Ti powder (purity ≥99.5%), 9.1 g Cr powder (purity ≥99%), 7.3 g Mo powder (purity ≥99%), and 4.4 g carbon black (purity ≥99%). The above raw materials were placed in a planetary ball mill and ball-milled at high energy in an Ar atmosphere using zirconia balls (ball-to-material ratio 12:1) (420 rpm, 32 h) to obtain Ti-Cr-Mo-C mechanical alloying precursor powder.

[0090] Take 180.0 g of mechanical alloying precursor powder and place it in a high-pressure reactor lined with polytetrafluoroethylene. Prepare a metal-organic compound solution: 3.8 g of chromium acetylacetone + 2.9 g of tetrabutyl titanate, dissolved in an ethanol / DMF mixed solvent (volume ratio 3:1, total solution volume 36.0 g).

[0091] The mechanically alloyed precursor powder was poured into the solution and ultrasonically dispersed for 45 min (power 250 W, frequency 40 kHz). Then the reaction vessel was sealed and placed in a solvothermal reactor. The temperature was increased to 185℃ at 5℃ / min and held for 7.5 h to carry out the solvothermal in-situ reaction.

[0092] After the reaction was completed, the mixture was naturally cooled to room temperature, filtered, washed three times with ethanol, and dried under vacuum at 60°C for 8 hours to obtain metal-organic composite coated particles.

[0093] The coated particles were placed in a tube furnace, and after purging oxygen with Ar gas (flow rate 70 mL / min) for 25 min, the temperature was increased to 720℃ at 6℃ / min and held for 3.0 h for low-temperature pyrolysis carbonization.

[0094] After naturally cooling to room temperature, the product was removed, lightly ground, and passed through a 400-mesh sieve to obtain Ti-Cr-Mo-C composite particles coated with a carbon residue layer containing metal elements.

[0095] Step 2: Preparation of GT35 steel-bonded cemented carbide Ingredients: 36.0 g of Ti-Cr-Mo-C composite particles coated with a carbon residue layer containing metallic elements, 63.8 g of pure iron powder (purity ≥99.5%), and 0.2 g of carbon black. The above components were placed in a planetary ball mill and dry-mixed and ball-milled under an Ar atmosphere (zirconia balls, ball-to-material ratio 8:1, rotation speed 380 rpm, time 18 h) to obtain a uniformly mixed powder.

[0096] The mixed powder is loaded into a unidirectional pressing mold with a diameter of 30 mm and pressed on a hydraulic press at a pressure of 420 MPa for 30 s to obtain a pressed blank.

[0097] The pressed blank is placed in a vacuum sintering furnace and evacuated to a vacuum level of 5×10. -3 After Pa, the temperature is increased to 1180℃ at 8℃ / min and held for 1.8 h; then increased to 1435℃ at 5℃ / min and held for 2.2 h; and then cooled to room temperature with the furnace.

[0098] The sintered body was placed in a box-type resistance furnace, heated to 880℃ and held for 35 min, then oil quenched; subsequently tempered in a muffle furnace at 180℃ for 2.5 h and air cooled.

[0099] Step 3: Performance Testing 1. Carbon content of the binder phase: The carbon content of the binder phase was calculated by subtracting the carbon content of the hard phase from the overall carbon content using a carbon-sulfur analyzer (combustion method). Each sample was measured twice and the average value was taken.

[0100] 2. Carbon content fluctuation range: 5 batches were prepared independently, and the average value ± standard deviation was calculated.

[0101] 3. Rockwell hardness (HRC): A hardness tester was used with a load of 150 kgf. Ten points were measured on each sample surface, and the average value was taken.

[0102] 4. Hardness fluctuation range: Statistical average of 5 batches ± standard deviation.

[0103] The test data is shown in Table 3 below: Example 3 uses Ti-Cr-Mo-C composite particles coated with a carbon residue layer containing metal elements. The average carbon content of the binder phase in 5 batches was 0.497 wt%, with a fluctuation range of only ±0.011 wt%, which is further reduced compared to Example 1 and Example 2. The average hardness was 62.6 HRC, with a fluctuation of only ±0.4 HRC. This indicates that the carbon residue layer containing metal elements formed in situ by the organometallic compound further improves the controllability of carbon release and enhances the interfacial stability, thereby achieving higher batch consistency of carbon content and uniformity of hardness.

[0104] Comparative Example 1 Step 1: Preparation of GT35 steel-bonded cemented carbide Raw material preparation: 35.0 g of pure TiC powder (purity ≥99%), 63.4 g of pure iron powder (purity ≥99.5%), 0.7 g of Cr powder (purity ≥99%), 0.7 g of Mo powder (purity ≥99%), and 0.6 g of carbon black. Place the above components in a planetary ball mill, add anhydrous ethanol as the wet grinding medium (ethanol:powder mass ratio 1:1), and zirconia balls (ball-to-material ratio 10:1). Grind at 350 rpm for 24 h.

[0105] After wet milling, the slurry was placed in a vacuum drying oven and dried at 80°C for 12 hours to remove ethanol, yielding a dried powder.

[0106] The dried powder is loaded into a unidirectional pressing mold with a diameter of 30 mm and pressed on a hydraulic press at a pressure of 420 MPa for 30 s to obtain a pressed blank.

[0107] The pressed blank is placed in a vacuum sintering furnace and evacuated to a vacuum level of 5×10. -3 After Pa, the temperature is increased to 1180℃ at 8℃ / min and held for 1.8 h; then increased to 1435℃ at 5℃ / min and held for 2.2 h; and then cooled to room temperature with the furnace.

[0108] The sintered body was placed in a box-type resistance furnace, heated to 880℃ and held for 35 min, then oil quenched; subsequently tempered in a muffle furnace at 180℃ for 2.5 h and air cooled.

[0109] Step 2: Performance Testing 1. Carbon content of the binder phase: The carbon content of the binder phase was calculated by subtracting the carbon content of the hard phase from the overall carbon content using a carbon-sulfur analyzer (combustion method). Each sample was measured twice and the average value was taken.

[0110] 2. Carbon content fluctuation range: 5 batches were prepared independently, and the average value ± standard deviation was calculated.

[0111] 3. Rockwell hardness (HRC): A hardness tester was used with a load of 150 kgf. Ten points were measured on each sample surface, and the average value was taken.

[0112] 4. Hardness fluctuation range: Statistical average of 5 batches ± standard deviation.

[0113] The test data is shown in Table 4 below: Comparative Example 1 used a traditional wet milling process with a large amount of carbon black added later. The average carbon content of the binder phase in 5 batches was 0.530 wt%, with a fluctuation range of ±0.074 wt%, which was much larger than that in the embodiment of this method. The average hardness was 61.7 HRC, but the fluctuation was ±2.9 HRC. This indicates that the oxygenation effect introduced during the wet milling process and the concentrated carbon addition method in the later stage are difficult to achieve stable control of the carbon content of the binder phase, resulting in significant hardness variation.

[0114] Comparative Example 2 Step 1: Preparation of solid solution modified TiC particles Raw material weighing: TiO2 148.6 g, Cr2O3 11.4 g, MoO3 7.2 g, carbon black 9.8 g. The above raw materials were placed in a planetary ball mill and ball-milled for 8 h (350 rpm) with zirconia balls (ball-to-material ratio 10:1) under Ar atmosphere.

[0115] The mixed powder was placed in a graphite crucible and placed in a high-temperature tube furnace. After purging oxygen with Ar gas (flow rate 80 mL / min) for 30 min, the temperature was increased to 1620℃ at 5℃ / min and held for 2.5 h to carry out the carbothermic reduction reaction.

[0116] After natural cooling, the particles are lightly ground through a 400-mesh sieve to obtain solid solution modified TiC particles.

[0117] Step 2: Preparation of GT35 steel-bonded cemented carbide Ingredients: 35.0 g of solution-modified TiC particles, 64.5 g of pure iron powder (purity ≥99.5%), and 0.5 g of carbon black. Place the above components in a planetary ball mill, add anhydrous ethanol as the wet grinding medium (ethanol:powder mass ratio 1:1), and zirconia balls (ball-to-material ratio 10:1). Grind at 350 rpm for 24 h.

[0118] After wet milling, the slurry was placed in a vacuum drying oven and dried at 80°C for 12 hours to remove ethanol, yielding a dried powder.

[0119] The dried powder is loaded into a unidirectional pressing mold with a diameter of 30 mm and pressed on a hydraulic press at a pressure of 420 MPa for 30 s to obtain a pressed blank.

[0120] The pressed blank is placed in a vacuum sintering furnace and evacuated to a vacuum level of 5×10. -3 After Pa, the temperature is increased to 1180℃ at 8℃ / min and held for 1.8 h; then increased to 1435℃ at 5℃ / min and held for 2.2 h; and then cooled to room temperature with the furnace.

[0121] The sintered body was placed in a box-type resistance furnace, heated to 880℃ and held for 35 min, then oil quenched; subsequently tempered in a muffle furnace at 180℃ for 2.5 h and air cooled.

[0122] Step 3: Performance Testing 1. Carbon content of the binder phase: The carbon content of the binder phase was calculated by subtracting the carbon content of the hard phase from the overall carbon content using a carbon-sulfur analyzer (combustion method). Each sample was measured twice and the average value was taken.

[0123] 2. Carbon content fluctuation range: 5 batches were prepared independently, and the average value ± standard deviation was calculated.

[0124] 3. Rockwell hardness (HRC): A hardness tester was used with a load of 150 kgf. Ten points were measured on each sample surface, and the average value was taken.

[0125] 4. Hardness fluctuation range: Statistical average of 5 batches ± standard deviation.

[0126] The test data is shown in Table 5 below: Unlike Example 1, Comparative Example 2 still employed a wet milling process in the subsequent powdering and forming stages, relying on concentrated carbon replenishment in the later stages, without constructing a carbon-coated or phased-release structure. The data shows that although Comparative Example 2 used (Ti,Cr,Mo)C solution-modified TiC particles, the average carbon content of the binder phase in the five batches was 0.513 wt%, with a fluctuation range of ±0.033 wt%, which is an improvement over Comparative Example 1 but still significantly higher than the example in this embodiment. The average hardness was 62.0 HRC, with a fluctuation of ±1.6 HRC. This comparative example verifies that when TiC is only solution-modified without addressing the carbon loss during wet milling and the instability of later carbon replenishment, the carbon content still fluctuates significantly, resulting in insufficient hardness consistency.

[0127] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for precisely controlling the carbon content of the binder phase in GT35 steel cemented carbide, characterized in that, Includes the following steps: S1. Weigh the Ti-Cr-Mo-C composite hard phase component, Fe powder and carbon supplement at a mass ratio of (32~38):(61.7~67.9):(0.1~0.3), and mix them evenly by dry mixing or ball milling in a low-oxygen medium to obtain a mixed powder, wherein Ti, Cr, Mo and C in the Ti-Cr-Mo-C composite hard phase component exist at least partially in the form of carbides or solid solution carbides; S2. Press the mixed powder into a compact; S3. The pressed blank is subjected to solid-phase sintering and liquid-phase sintering in sequence to obtain a sintered body; S4. The sintered body is heat-treated to obtain GT35 steel-bonded cemented carbide.

2. The method for precisely controlling the carbon content of the cemented carbide binder phase in GT35 steel according to claim 1, characterized in that, In the Ti-Cr-Mo-C composite hard phase component, the total mass content of Cr and Mo is 3~12 wt%, the mass ratio of the two is (1~2):1, the mass content of C is 1.5~3.5 wt%, and the balance is Ti.

3. The method for precisely controlling the carbon content of the cemented carbide binder phase in GT35 steel according to claim 2, characterized in that, The Ti-Cr-Mo-C composite hard phase component is at least one of the following a or b: a)(Ti,Cr,Mo)C solid solution particles; b) Carbon-coated Ti-Cr-Mo-C composite particles, consisting of Ti-Cr-Mo-C composite core particles and a carbon residual layer covering them.

4. The method for precisely controlling the carbon content of the cemented carbide binder phase in GT35 steel according to claim 3, characterized in that, The (Ti,Cr,Mo)C solid solution particles are prepared by at least one of the following methods c or d: c) Carbothermic reduction method: After mixing the oxide raw materials containing Ti, Cr and Mo with the carbon source, the carbothermic reduction reaction is carried out under high temperature inert or reducing atmosphere to generate solid solution particles. d) Mechanical alloying method: Ti source, Cr source, Mo source and carbon source powders are subjected to high-energy ball milling alloying treatment to form solid solution particles.

5. The method for precisely controlling the carbon content of the cemented carbide binder phase in GT35 steel according to claim 4, characterized in that: In the carbothermic reduction method, the oxide raw materials containing Ti, Cr, and Mo are selected from TiO2, Cr2O3, and MoO3, and the carbon source is selected from at least one of carbon black, activated carbon, and graphite powder. The carbothermic reduction reaction temperature is 1300~1800℃, and the temperature is maintained for 1~4 h. In the mechanical alloying method, the Ti source is selected from Ti powder, the Cr source is selected from Cr powder, the Mo source is selected from Mo powder, and the carbon source is selected from at least one of carbon black and graphite powder. The high-energy ball milling alloying treatment adopts a planetary ball mill or a vibratory ball mill with a rotation speed of 300~600 rpm, a ball-to-material mass ratio of (8~20):1, and a ball milling time of 10~50 h.

6. The method for precisely controlling the carbon content of the cemented carbide binder phase in GT35 steel according to claim 3, characterized in that, The carbon-coated Ti-Cr-Mo-C composite particles are prepared by at least one of the following methods e and f: e) After mixing and coating the Ti-Cr-Mo-C composite core particles with the organic carbon precursor solution, the mixture is subjected to low-temperature carbonization treatment to allow the organic precursor to pyrolyze and form a carbon residue layer. f) The Ti-Cr-Mo-C composite core particles are mixed with a metal-organic compound solution, and a metal-organic composite layer is formed in situ on the particle surface by solvothermal or vapor deposition. Then, a low-temperature pyrolysis carbonization treatment is performed to transform the metal-organic composite layer into a metal-doped carbon residue layer.

7. The method for precisely controlling the carbon content of the cemented carbide binder phase in GT35 steel according to claim 6, characterized in that, In method e: The organic carbon precursor is selected from at least one of phenolic resin, polyvinyl alcohol, furfural resin, glucose, and polyacrylonitrile; The solvent for the solution is selected from at least one of ethanol, water, and acetone; The mass ratio of Ti-Cr-Mo-C composite core particles to organic carbon precursor solution is (5~20):1; Low-temperature carbonization is carried out under inert atmosphere or vacuum conditions, with a carbonization temperature of 400~700℃, a holding time of 0.5~5 h, and a heating rate of 2~10℃ / min.

8. The method for precisely controlling the carbon content of the cemented carbide binder phase in GT35 steel according to claim 6, characterized in that, In method f: The organometallic compound is selected from at least one of titanates, molybdates, organochromium compounds, and metal acetylacetonates; The solution solvent is selected from at least one of ethanol, isopropanol, N,N-dimethylformamide, dimethyl sulfoxide, and water; The mass ratio of Ti-Cr-Mo-C composite core particles to organometallic compound solution is (5~25):1; The solvothermal and vapor phase deposition processes were carried out in a closed container and a vapor phase reactor, respectively. The solvothermal reaction temperature was 120~250℃ and the holding time was 2~24 h. The vapor phase deposition temperature was 200~500℃ and the deposition time was 0.5~8 h. The low-temperature pyrolysis carbonization treatment is carried out under an inert atmosphere or vacuum, with a carbonization temperature of 500~900℃, a holding time of 0.5~6 h, and a heating rate of 2~15℃ / min.

9. The method for precisely controlling the carbon content of the cemented carbide binder phase in GT35 steel according to claim 3, characterized in that, In step S3: Solid-state sintering is carried out under vacuum or slightly positive pressure inert atmosphere, with a sintering temperature of 1000~1250℃, a holding time of 0.5~3 h, and a heating rate of 3~15℃ / min. Liquid phase sintering is carried out under vacuum or slightly positive pressure inert atmosphere, with a sintering temperature of 1350~1480℃, a holding time of 1~4 h, and a heating rate of 2~10℃ / min.

10. The method for precisely controlling the carbon content of the cemented carbide binder phase in GT35 steel according to claim 1, characterized in that: In step S2, the pressing molding adopts unidirectional or isostatic pressing, the pressing pressure is 200~600 MPa, and the holding time is 5~60 s; In step S4, the heat treatment includes quenching and tempering. Quenching is performed by oil quenching or salt bath quenching at a temperature of 800~950℃, holding for 0.2~1 h and then rapidly cooling. Tempering is performed in air or a protective atmosphere at a temperature of 150~350℃ and holding for 1~4 h.

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